dosage of cbd oil for anxiety

Dosage, Efficacy and Safety of Cannabidiol Administration in Adults: A Systematic Review of Human Trials

The data supporting the findings of this study are available from the corresponding author upon request.


Considering data from in vitro and in vivo studies, cannabidiol (CBD) seems to be a promising candidate for the treatment of both somatic and psychiatric disorders. The aim of this review was to collect dose(s), dosage schemes, efficacy and safety reports of CBD use in adults from clinical studies. A systematic search was performed in PubMed, Embase and Cochrane library for articles published in English between January 1, 2000 and October 25, 2019. The search terms used were related to cannabis and CBD in adults. We identified 25 studies (927 patients; 538 men and 389 women), of which 22 studies were controlled clinical trials (833 patients) and three were observational designs (94 patients) from five countries. Formulations, dose and dosage schemes varied significantly between studies. Varying effects were identified from the randomized controlled trials (RCTs), more apparent effects from non-RCTs and minor safety issues in general. From the controlled trials, we identified anxiolytic effects with acute CBD administration, and therapeutic effects for social anxiety disorder, psychotic disorder and substance use disorders. In general, studies were heterogeneous and showed substantial risks of bias. Although promising results have been identified, considerable variation in dosage schemes and route of administration were employed across studies. There was evidence to support single dose positive effect on social anxiety disorder, short medium-term effects on symptomatic improvement in schizophrenia and lack of effect in the short medium-term on cognitive functioning in psychotic disorders. Overall, the administration was well tolerated with mild side effects.


Cannabis sativa L. has a long tradition of medical use. However, its clinical use has been limited due to the effects on the central nervous system and the possibility of drug abuse and addiction. The plant exudes a resin containing a mix of cannabinoids with two principal components, Δ9-tetrahydrocannbinol (THC) and cannabidiol (CBD). The structure and configuration of CBD was discovered in the 60s and has gained particular attention due to the lack of psychotropic activity. Because of its excellent tolerability in humans, the lack of psychoactive action and the low abuse potential, it seems an ideal candidate for use in a clinical context [1].

In addition to its good safety profile and the lack of psychoactive effects, CBD presents also a wide range of therapeutic effects [2]. Possibly for these reasons, CBD is currently one of the most studied cannabinoids [3]. Several experimental in vitro and in vivo studies have shown that CBD has a broad range of therapeutic applications, displaying anti-inflammatory and immunomodulatory properties [4], anti-psychotic [5], analgesic [6] and anti-epileptic [7] effects, among others. Compared to Δ9-THC, CBD shows low affinity for cannabinoid receptor type 1 (CB1) and type 2 (CB2) [8]. CB1 receptors are mainly found in the terminals of central and peripheral neurons and CB2 receptors mainly in immune cells [9]. Several in vitro studies have shown that CBD, at low concentrations, has weak CB1 and CB2 antagonistic effect [10]. It has also been reported that it behaves as a negative allosteric modulator of CB1, meaning that CBD does not activate the receptor directly but alter the potency and efficacy of orthosteric ligands of this receptor: Δ9-THC and 2-arachidonoylglycerol (2-AG) [11]. These preliminary results need further validation, but may explain the ability of CBD to antagonize some of the effects of Δ9-THC reported in in vitro, in vivo and clinical human studies [12]. It has also been suggested that the role of CBD as an allosteric modulator of CB1 can explain its therapeutic role in the treatment of central and peripheral nervous system disorders [2]. CBD has also shown to have a strong inhibition effect of neutrophil chemotaxis and proliferation. In addition, it may induce stimulation of arachidonic acid release, reducing prostaglandin E2 (PGE2), and nitric oxide (NO) production. Furthermore, CBD reduces the expression of specific interleukins (IL-12 while increasing that of IL-10) by macrophages, and decreases the production and release of pro-inflammatory cytokines, such as IL-1, IL-6 and interferon gamma (IFNγ) from lipopolysaccharide (LPS)-activated microglial cells [13]. The role of CBD as an inverse agonist of CB2 receptor may explain its known anti-inflammatory effects but this needs further investigation. There is also evidence of an antagonistic effect of CBD at the novel cannabinoid receptor G protein-coupled receptor 55 (GPR55), emerging from in vitro and in vivo studies. GPR55 has a role in bone physiology via regulating osteoclast function, formation and ultimately bone mass. CBD may affect the endocannabinoid system also indirectly, for example CBD can affect the endocannabinoid tone by increasing availability of anandamide; one possible mechanism is by inhibition of fatty acid amide hydrolase (FAAH), the enzyme that hydrolyzes the endocannabinoid anandamide [14].

However, not all physiological effects of CBD are mediated by cannabinoid receptors. Indeed CBD has numerous targets outside the endocannabinoid system and the cannabinoid receptor independent action is the subject of recent pharmacological studies on CBD [2]. Some of these physiological effects such as anti-inflammatory and immunosuppressive effect are mediated by more than one target [8]. The anti-inflammatory immunosuppressive effects are possibly mediated by activation of adenosine receptors, A1A and A2A and strychnine-sensitive α1 and α1β glycine receptors and the inhibition of the equilibrative nucleoside transporter [8]. The activity of CBD at one defined target may also elicit different physiological effects. For example, anti-inflammatory action and suppression of neuropathic pain are mediated by the same glycine receptors or anxiolytic, panicolytic and anti-depressant effects via serotonin 5HT1A receptor sub-type [8]. Pisano et al (2017) showed an in-depth review of the molecular pharmacology of CBD [2]. Despite the great number of studies published on molecular pharmacology of CBD, the exact pharmacological action of CBD remains not fully characterized and ongoing efforts are directed toward fully elucidating these mechanisms [3].

The clinical studies on the effects of CBD date back to the 80s but recently the number of studies and registered trials evaluating the effectiveness of this compound has risen exponentially. Currently, CBD is commercially available in different formulations and used for several health conditions but could be indicated for several diseases or disorders in addition to or in replacement of medical marijuana or other medical therapy. However, it remains unclear in which form and dose CBD should be administered to assess safety and efficacy across indications. This might further be complected by the nature of altered dose depending on indication of intervention. To highlight administration and dosage for known indications (e.g. diseases and disorders), this systematic review reports the current evidence, literature and experiences of how and in which dose CBD could be administered as well as efficacy and safety reports.


Study eligibility criteria

One author (CL) systematically searched PubMed, EMBASE and the Cochrane Library for published studies in English. The search was last updated on November 5, 2019. We included human studies of reporting more than 10 adult patients. We restricted our search to studies published after the year of 2000 with no demographic limitation. We included studies with single treatment of CBD, e.g. studies with other cannabinoid add-on therapy or adjuvant regimes were excluded. Studies must report dosage and dosage schemes to be included. There was no limitation regarding study design. Studies on pediatric populations were excluded. Only studies published in English, from 2000 to the date last databases were accessed. Full-text articles were interdependently assessed by two reviewers and eventual disagreement was resolved through consensus.

PubMed, Embase and Cochrane database were searched with all combinations of CBD and dosage in human studies. Reference lists of included studies were evaluated, and if needed, authors were contacted for further information.

Data collection and critical appraisal

We extracted the following data: condition and symptoms, year of publication, country, study population, number of patients, age, gender, weight, outcome measures, effect of treatment, side effects, dosage, administration form (pills, smoking, oil, etc.), length of treatment, doses, product/brand, isolated CBD or full spectrum and funding/sponsors.

The methodological quality of randomized controlled trials (RCTs) was assessed using the Cochrane risk of bias tool [15]. If all domains were judged as being at low risk of bias, the study was considered at low risk of bias. If at least one domain was rated high, the study was considered at high risk of bias. In situations that differ from those described above, the study was considered at unclear rick of bias. Data extraction and risk of bias was assessed by two independent reviewers and disagreements were solved by a third reviewer or with consensus.


Clinical heterogeneity was assessed by grouping studies by indication and outcome (including disease-specific outcomes and if specified adverse events (AEs)) and scheme of drug administration. Data were too heterogeneous to be pooled, so we used a narrative synthesis.

To rate the overall quality of evidence for risk of bias, the Grading of Recommendations Assessment, Development and Evaluation (GRADE) was used for each outcome of interest across all domains: methodological limitations of the studies, indirectness, imprecision, inconsistency and publication bias [16].


Study selection and characteristics

We identified 362 studies of which 85 were assessed for full-text eligibility ( Fig. 1 ). Finally, 25 studies were included: 22 controlled clinical trials and three non-controlled (single arm) trials [10-34]. Among controlled clinical trials, two were non-RCTs and 20 RCTs (14 individually randomized parallel group trial, five individually randomized cross-over trials and one cluster randomized cross-over trial). Studies were conducted in five countries with the majority of studies being conducted in the UK. All studies were reported in full length journal articles. The administration of CBD varied from single doses to chronic administration, up to 48 weeks. The pure form of CBD was used in the majority of the studies except for two studies using seed CBD oil and CBD-rich botanical extracts. The most common form of drug administration was in the form of oral capsules, and other forms were vaporization and sublingual oil. The most common comparator was placebo only one study used an active-control group. Results for controlled clinical trials and non-controlled studies are presented in Table 1 [17-37] and Table 2 [38-40], providing a summary of the included studies and their principal findings.

PRISMA flow diagram of literature search and selection process. PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Table 1

Author, year of publication Population (no. of participants) Study design CBD dose and scheme Formulation/route Primary outcome Measures Effect
  Bergamaschi et al (2011) [17] Social anxiety disorder patients (24) IR parallel group trial 600 mg; single dose Oral capsules Anxiety Visual analogue mood scale (sub-scales; anxiety, cognitive impairment, discomfort and alert) CBD significantly reduced anxiety, cognitive impairment, discomfort and alert during simulation public speaking test
  Crippa et al (2011) [22] Social anxiety disorder patients (10) IR cross-over trial 400 mg; single dose Oral capsules Anxiety Visual analogue mood scale Acute administration reduced subjective anxiety
  Arndt et al (2017) [25] Healthy volunteers (38) IR cross-over trial 300, 600 and 900 mg; single dose Oral solution Reactivity to negative stimuli Behavioral tasks Single doses of CBD had little effect on reactions to negative emotional stimuli
  Crippa et al (2004) [21] Healthy volunteers (10) IR cross-over trial 400 mg; single dose Oral capsules Anxiety Visual analogue mood scale (sub-scales; anxiety, physical sedation, mental sedation and other feelings and attitudes) CBD significantly decreased subjective anxiety and increased mental sedation
  Zuardi et al (2017) [19] Healthy volunteers (60) IR parallel group trial 100, 300 and 900 mg; single dose Oral capsules Anxiety Visual analogue mood scale (anxiety and sedation factors) CBD 300 mg reduced subjective anxiety measures and presented lower sedation level when compared with clonazepam. This was not observed with CBD 100 and 900 mg.
  Martin-Santos et al (2012) [23] Healthy volunteers (16) NR controlled trial 600 mg; single dose Oral Anxiety Spielberger State Anxiety Inventory, visual analogue mood scale There was no difference between CBD and placebo on anxiety levels.
  Bhattacharyya et al (2010) [24] Healthy volunteers (15) NR controlled trial 600 mg; single dose Oral capsules Anxiety Visual analogue mood scale- tranquilization and calming sub-scale. CBD single dose reduced anxiety levels.
  Linares et al (2019) [18] Healthy volunteers (57) IR parallel group trial 150, 300 and 600 mg; single dose Oral capsules Anxiety Visual analogue mood scale 300 mg of CBD significantly reduced anxiety during simulation public speaking test
  Das et al (2013) [27] Healthy volunteers (48) IR parallel group trial 32 mg; single dose Inhalation/vaporized Extinction and consolidation Skin conductance and shock expectancy measures CBD enhanced consolidation of extinction learning
  Hindocha et al (2015) [26] High and low cannabis use and high and low schizotipy (48) CR cross-over trial 16 mg; single dose Inhalation/vaporized Emotional processing Computer-based emotional processing task CBD improved recognition of emotional facial affect.
  Hundal et al (2018) [20] Non-clinical high paranoid group (32) IR parallel group trial 600 mg; single dose Oral capsules Anxiety Beck’s anxiety inventory CBD apparently seemed to increase anxiety levels.
Psychotic disorders
  Hallak et al (2010) [31] Schizophrenia patients (28) IR parallel group trial 300 or 600 mg; single dose Oral capsules Cognitive functioning Stroop color word test 300 and 600 mg of CBD do not lead to cognitive improvement
  Boggs et al (2018) [28] Chronic schizophrenia patients (42) IR parallel group trial 600 mg/day; 6 weeks Oral capsules Psychotic symptoms, cognitive functioning Positive and negative syndrome scale T score of MATRICS consensus cognitive battery Psychotic symptoms improved in both groups without significant difference, cognitive functioning improved only in placebo group.
  Leweke et al (2012) [29] Acutely psychotic patients (32) IR parallel group trial a 200 mg/day up to 800 mg/day; 4 weeks Oral capsules Psychotic symptoms Positive and negative syndrome scale; brief psychiatric rating scale CBD is as effective as amisulpride in improving psychotic symptoms
  McGuire et al (2018) [30] Schizophrenia patients (88) IR parallel group trial 1,000 mg/day; 6 weeks b Oral solution Psychotic symptoms Positive and negative syndrome scale, clinical global impressions scale Treatment with CBD improved positive psychotic symptoms and clinicians’ impressions of illness improvement.
Cognitive functioning, level of functioning Brief assessment of cognition in schizophrenia; global assessment of functioning scale Improvement in cognitive performance and in the level of overall functioning with CBD although does not reach statistical significance.
  Hundal et al (2018) [20] Non-clinical high paranoid group (32) IR parallel group trial 600 mg; single dose Oral capsules Persecutory ideation State social paranoia scale, community assessment of psychic experiences scale CBD had no effect on precursory thinking and psychotic-like experiences
Cannabis use disorder
  Haney et al (2016) [32] Healthy cannabis smokers (32) IR cross-over trial 200, 400 and 800 mg; single dose Oral capsules Cannabis subjective effects Subjective mood and drug effects measured with visual analogue scale CBD did not alter the subjective effects of smoked cannabis
Nicotine addiction
  Morgan et al (2013) [33] Tobacco smokers (24) IR parallel group trial 400 µg; 1 week Inhalation/vaporized Reduction in the number of cigarettes smoked Number of cigarettes smoked CBD reduced the number of cigarettes smoked during treatment and at follow-up
  Hindocha et al (2018) [34] Tobacco smokers (30) IR parallel group trial 800 mg; single dose Oral capsules Nicotine withdrawal Visual probe task and pleasantness rating task CBD reduced the salience and pleasantness of cigarette cues, compared with placebo but did not influence tobacco craving or withdrawal
  Jadoon et al (2016) [35] Patients with type 2 diabetes and dyslipidemia (62) IR parallel group trial 200 mg/day; 13 weeks Oral capsules HDL cholesterol concentrations Enzymatic calorimetric assays CBD did not produce any effect on HDL levels compared to placebo
Crohn’s disease
  Naftali et al (2017) [36] Patients with diagnosis of Crohn’s disease (19) IR parallel group trial 20 mg/day; 8 weeks b Sublingual oil Disease activity Crohn’s disease activity index A reduction in disease activity at the end of the study but no significant difference with placebo.
Ulcerative colitis
  Irving et al (2018) [37] Patients with mild to moderate ulcerative colitis (60) IR parallel group trial 50 mg up to 250 mg/day; 10 weeks a, b, c Oral capsules Remission at the end of treatment Mayo score of ≤ 2 The primary endpoint was negative but CBD may be beneficial for symptomatic treatment of ulcerative colitis

a Active-controlled trial, amisulpride. b Concomitant treatment. c CBD-rich botanical extracts capsules contained other compound (up to 4.7% THC). IR: individually randomized; NR: non-randomized; CR: cluster randomized; CBD: cannabidiol; HDL: high-density lipoprotein.

Table 2

Author/year of publication Indication No. of participants Dose evaluated (administration scheme) Administration method Follow-up Outcome Measure Effect
Szaflarski et al (2018) [38] Epilepsy 60 5 up to 50 mg/kg/day d Oral oil 48 weeks Seizure control Seizure frequency, Chalfont seizure severity scale Improved compared to baseline
Palmieri et al (2019) [39] Skin disorders 20 N/A (two times a day/3 months) Topical gel 3 months Hydration Hydration probe Improved compared to baseline
Transepidermal water loss DermaLab ® USB instrument a Improved compared to baseline
Skin elasticity ElastiMeter® b Improved compared to baseline
Severity of atopic dermatitis Scoring atopic dermatitis Improved compared to baseline
Severity of acne Acne disability index Improved compared to baseline
Severity of psoriasis Psoriasis area severity index Improved compared to baseline
Palmieri et al (2017) [40] ADR following HPV vaccine 12 25 mg/mL, 150 mg/mL (one time/day × 3 months) c Sublingual oil drops 3 months Quality of life Medical outcome short-form health survey questionnaire Improved compared to baseline

a Cortex Technologies, Hadsund, Denmark. b Delfin Technologies, Kuopio, Finland. c Concomitant treatment for the condition with anti-oxidant and pain killer. d Concomitant treatment with anti-seizure drugs. N/A: non-available; HPV: human papillomavirus; ADR: adverse drug reaction.

The risk of bias within studies

Among the randomized trials, three were judged at low risk of bias, eight were judged at high risk of bias and nine at uncertain risk. Major potential sources of bias were frequent in the following domains: randomization process and selection of the reported results. Most studies reported were randomized and double-blinded but few reported methods of randomization or participants and outcome assessor blinding. Selective outcome reporting was also a potential source of bias, since some studies did not report data for all outcomes specified in the methods section or trial register or changed the primary outcome from what was specified in the trial register.

Most studies reported outcomes differently and even in cases where the same outcome was reported it was measured differently. Outcome level assessment was performed only for anxiety in social anxiety disorder (SAD) and psychotic symptoms and cognitive function in schizophrenia patients following recommendations applying GRADE approach in narrative synthesis [9]. GRADE rating is presented in Table 3 . Two studies assessed anxiety in treatment-naive SAD populations, and three assessed cognitive function and positive and negative symptoms in schizophrenia patients.

Table 3

Outcomes No. of participants (studies) follow-up Certainty of the evidence (GRADE) a Impact
Anxiety symptoms assessed with visual analogue mood scale 44 (two RCTs) ⨁⨁◯◯
All studies showed a reduction in symptoms compared to placebo.
Psychotic symptoms assessed with positive and negative syndrome scale, brief psychiatric rating scale 171 (three RCTs) ⨁⨁⨁◯
Two studies showed improvement in psychotic symptoms. Some variability in the intervention (doses) and population (stage of illness) was noted.
Cognitive function assessed with T score of MATRICS consensus cognitive battery, stroop color word test, composite score on the brief assessment of cognition in schizophrenia 148 (three RCTs) ⨁⨁⨁◯
Two studies showed no improvement in cognitive function. One showed only small improvements.

The outcome of interest are: anxiety symptoms, psychotic symptoms and cognitive function. A pooled effect estimate was not available and a narrative synthesis of the evidence was provided. a Symbols are used to describe certainty in evidence profiles. High certainty: ⨁⨁⨁⨁; Moderate certainty: ⨁⨁⨁◯; Low certainty: ⨁⨁◯◯; Very low certainty: ⨁◯◯◯. RCT: randomized controlled trial.

Anxiety disorder

Anxiety was assessed in 11 studies (358 participants) [17-27]. Anxiety was the main outcome in eight studies, while possible anxiolytic effects were evaluated in the remaining three studies, through indirect measures such as emotional processing, reactivity to negative stimuli, etc. Among the studies providing data on anxiety, there were only two restricted analyses to patients with anxiety disorders and another to non-clinic paranoia patients. Nine studies were randomized clinical trials: one of the studies was judged at low risk of bias, four at uncertain risk and four at high risk. Single doses of pure CBD 150 – 900 mg in the form of gelatin capsules were administered in the majority of the cases. Two individually randomized parallel-group trials evaluated the effect of CBD on subjective anxiety on patients with SAD [17] or healthy subjects [18, 19] during simulated public speaking. These studies reported that acute oral administration of 600 mg (SAD subjects) and 300 mg (healthy subjects) of CBD reduced anxiety assessed by the visual analogue mood scale compared to placebo. Linares et al (2018) and Zuardi et al (2017) also tested other doses and observed no effect on anxiety levels after acute administration of 150, 600 and 900 mg of CBD on anxiety levels. No effect was found for the physiological measures such as heart rate and systolic/diastolic blood pressure [17-19]. Another small, individually randomized parallel-group trial, reported that acute administration of oral CBD (600 mg) had a negative effect on anxiety levels, measured with the Beck’s anxiety inventory, compared to placebo [20]. Single oral doses of 400 and 600 mg decreased anxiety and increased mental sedation measured with visual analogue mood scale in two individually randomized cross-over trials [21, 22]. Two small non-RCTs administered 600 mg of oral CBD to health volunteers. One found no difference between placebo and CBD group on anxiety levels [23], while the other found a reduction on anxiety measured with visual analogue mood scale [24].

One randomized cross-over trial measured reactivity to negative stimulus through behavioral tasks and reported no effect at different incremental single doses of CBD (300, 600 and 900 mg). This measure was based on the hypotheses that drug anxiolytic effect should be manifested through changes in responses to negative stimuli, which also occur with single doses for common anxiolytics [25]. A cluster randomized cross-over trial assessed the effect of small doses (16 mg) administered through inhalation on fear extinction and consolidation and found that it was effective when compared to placebo [26]. Das et al (2013) found that acute administration of 32 mg of CBD, before training, enhances extinction of conditioned fear responses [27].


Four randomized parallel-group trials (196 participants) assessed the role of CBD on cognitive impairment and psychotic symptoms in patients with psychotic disorders (schizophrenia) [28-31]. One study was judged as being at high risk of bias and three at uncertain risk of bias. Studies included patients with a confirmed diagnosis of schizophrenia. CBD was administered orally, in the form of oral gelatin capsules with doses ranging from 600 to 1,000 mg/day and the effects were compared to a placebo and active control. Boggs et al (2018) assessed the effects of CBD (600 mg/day for 6 weeks) as an adjunctive treatment in chronic schizophrenia patients, for a period of 6 weeks. No significant difference was observed between placebo and CBD group on cognitive function and psychotic symptoms [28]. Leweke et al (2012) included a small group of acute schizophrenia patients who were administered 200 up to 800 mg/day for 4 weeks or amisulpride, a potent antipsychotic. CBD was as effective as amisulpride in improving psychotic symptoms and associated with marked tolerability and safety, when compared with amisulpride [29]. McGurie et al (2019) administered 1,000 mg/day for 6 weeks to a group of schizophrenia patients as an adjunct to current antipsychotic treatment and found a significant improvement on positive psychotic symptoms and clinicians’ impressions of illness improvement. Despite improvement on cognitive function and overall level of functioning, no significant difference was found compared to placebo [30]. Hallak et al (2010) included a small group of heterogeneous schizophrenia patients and administered a single dose of CBD (300 or 600 mg). They found no effect of CBD on selective attention, measured by Stroop color and word test [31].

Substance use disorder

In a randomized cross-over design trial, Haney et al (2016) tested a range (200, 400 and 800 mg) of oral single doses of pure CBD, on cannabis smokers to assess the reinforcing subjective and psychological effects of smoked cannabis. The authors found no evidence with this treatment and dose scheme, and CBD can reduce the reinforcing or positive effects of smoked cannabis in current smokers [32]. Optional use of inhaled pure CBD (400 µg/dose) over 1 week produced positive effects with regard to nicotine addiction, as measured by a reduction on the number of cigarette smoked in a group of healthy smokers willing to quit the habit. However, CBD did not show effect on carving symptoms [33]. After overnight tobacco abstinence single doses of 800 mg of CBD reduced the salience and pleasantness of cigarette cues which indicate that CBD may have a potential effect on motivational aspects of addiction [34]. Two studies were judged at uncertain risk of bias and one at high risk.

Other conditions

Three RCTs, all individually randomized parallel group, reported on different medical conditions (one study for each category) [28-37]. Doses ranged from 20 to 250 mg/day with treatment duration from 8 to 13 weeks. Isolated compound or plant exacts rich in CBD were administered in the form of hard oral capsules or oil. One study was judged at uncertain risk of bias and two at high risk.

In one trial, 200 mg/day was administered for 13 weeks as an adjunct to current treatment to patients with type 2 diabetes. Compared to placebo, CBD did not have a significant effect on the level of high-density lipoproteins, the primary endpoint for this study [35]. The effect of oral administration of CBD (20 mg/day for 8 weeks) on disease activity assessed by the Crohn’s disease activity index was evaluated in a small group of patients with long-standing Crohn’s disease taking concomitant medications. CBD had no effect on disease activity at the end of treatment and at 2 weeks follow-up [36]. Irvin et al (2018) reported no effects of CBD-rich extracts (100 mg/day up to 250/day for 8 weeks) added to current treatment and administrated in the form of oral capsules to patients diagnosed with ulcerative colitis [37].

Non-controlled intervention studies

A label single arm trial [38] assessed long-term use of isolated CBD (5 mg/kg/day incremental doses in some patients reaching 2,000 mg/day) as an adjunct to anti-epileptic drugs, in patients refractory to conventional anti-seizure drugs and reported a decrease in seizure frequency (144.4 to 52.2, P = 0.01) and severity measured with the Chalfont seizure severity scale (from 80.7 at baseline to 39.2, P < 0.0001) at week 12, with values being stable thereafter (total follow-up 48 weeks). The other two studies [39, 40] included reported on the chronic administration effect of CBD in the form of a topical cream for skin disorders and sublingual oil drops (25 mg/day up to 150 mg/day for 12 weeks) for adverse drugs reaction (ADR) following human papilloma virus (HPV) vaccine, with a 3-month follow-up period each. The topical application produced positive results for serous skin inflammatory conditions such a psoriasis, acne and related scars, with no side effects being reported [39]. The sublingual administration of CBD also improved the quality of life in girls presenting with ADR following HPV vaccine when added to standard treatment. The evidence however arises from two case series and this should be taken into consideration when considering the results from this study [40].

AEs were reported in 10 studies. In most studies reporting on AEs [20, 28-30, 35-38, 40, 41], CBD was administered chronically, with follow-up ranging from 6 to 48 weeks, except for two studies where AEs were reported after a single dose of CBD (600 and 750 mg, respectively) [20-41]. The total number of reported patients, withdrawing from the study due to experience of side effects, was 16 in the CBD group. One study reported that side effects did not differ between the CBD and placebo groups after 8 weeks of follow-up [36], and another study reported a decrease of AEs 12 weeks after CBD initiation [38]. In another study side effects were monitored by answering question to a questionnaire [37]. The only study comprising CBD effects with an active group receiving an antipsychotic drug, amisulpride, in patients with schizophrenia reported that the CBD group had fewer extrapyramidal symptoms, less weight gain and prolactin release [29]. Results for the remaining studies, by indication and follow-up, for the number of participants experiencing any AEs compared to placebo AEs, classified by primary system organ class are reported in Table 4 .

Table 4

Follow-up < 1 day Follow-up 1 week Follow-up 10 weeks Follow-up 13 weeks
Cannabidiol (%) Placebo (%) Cannabidiol (%) Placebo (%) Cannabidiol (%) Placebo (%) Cannabidiol (%) Placebo (%)
Subjects experiencing any TEAE (%) 66.7 62.5 100 83.3 90 48 84.6 92.9
Nervous system disorders 33.3 37.5 66.7 33.3 83 26
Gastrointestinal system disorders 16.7 50.0 66.7 50.0 38 16
Infections and infestations 22.2 0 0 0
Psychiatric disorders 0 0 24 3
General disorders and administration site conditions 22.2 50.0 21 10
Musculoskeletal and connective tissue disorders 0 16.7 14 0
Skin and subcutaneous tissue disorders 2.2 16.7 3 0


This systematic review assessed the dosage schemes, effects and safety issues associated with the use of CBD. We included 20 RCTs, two non-RCTs and three observational studies for all indications of CBD use. In summary, 20 RCTs evaluated efficacy of CBD-use for schizophrenia, anxiety, Crohn’s disease, ulcerative colitis, dyslipidemia, nicotine addiction and cannabis use disorder. Most of these studies reported positive effect of CBD on anxiety, schizophrenia, tobacco addiction and minor effects or no effect on primary outcome measures for Crohn’s disease, ulcerative colitis, dyslipidemia and cannabis use disorder. All observational studies (skin disorders, ADR following HPV vaccine and epilepsy) reported positive effect of CBD when compared to baseline measures.

Regarding safety issues, most studies reported no AEs with acute administration and mild to moderate adverse effects with chronic administration. In comparison to other drugs, a better side effect profile was presented [29, 30]. The chronic administration of CBD for most of the included studies had a duration of few weeks (4 – 6 weeks). There is a need for longer term safety data and systematic/uniform reporting of AEs to better weight benefit and harms in future reviews. At least, two systematic reviews have been published on safety and side effects of CBD. The comprehensive review by Bergamaschi et al included animal and clinical studies reporting a favorable safety profile of CBD in humans [42]. The other review was an update of the previous focusing more on clinical data. The authors reported that most commonly side effects were tiredness, diarrhea and changes of appetite/weight. In comparison to other treatments used for epilepsy and psychotic disorders, CBD administration presented fewer side effects [43].

Most of the studies included in this review showed an improvement of anxiety levels after single doses of oral CBD with doses ranging from 300 to 600 mg [17-19, 21, 22, 24, 26, 27]. It is important to note that only two studies included a clinical population (SAD) while the majority involved healthy subjects. Both studies tested acute administration of CBD and found a reduction in subjective anxiety. A systematic review on specific anxiety conditions which included data from clinical and pre-clinical studies found strong evidence arising from pre-clinical studies to support the anxiolytic effects of CBD, and similarly that evidence from human studies was limited to acute dosing in mostly healthy subjects [44]. There is a need for better designed studies to evaluate the therapeutic potential of CBD in this clinical population, possibly with chronic dosing in a relevant clinical population.

A systematic review providing evidence from clinical studies, mainly randomized clinical trial and case series, on the efficacy of CBD in the treatment of schizophrenia and/or substance abuse disorders observed large differences in study population, doses and administration [45]. In the present review, two principal outcomes were considered for schizophrenia patients, psychotic symptoms and cognitive functioning. CBD had positive effect on psychotic symptoms especially in acutely psychotic patients [29], while it had small or no effect on chronic schizophrenia patients who had been treated with anti-psychotics. The possibility that larger effects may be observed for patients in the early phases of the disease had been suggested [28, 45]. Regarding cognitive function little or no effects were observed after chronic or acute administration. A recent systematic review including 27 RTCs that investigated the effects of CBD on different psychiatric disorders such as psychosis, moods disorders and anxiety found that because of large heterogeneity across studies CBD doses, formulations and the study populations, it was not possible to make definitive conclusion about clinical effects [44]. The authors suggested that large-scale placebo controlled studies are needed to investigate the effects of CBD as an adjunct treatment for psychiatric disorder [46].

No effect was reported in the studies included in this review for the treatment of Crohn’s disease, ulcerative colitis and type 2 diabetes with doses ranging between 20 and 250 mg/day for a treatment duration of 8 – 13 weeks [38-40]. While positive results were reported on seizure improvement with doses ranging from 350 to 2,000 mg/day and on the quality of life for patients with ADRs following HPV vaccine, with doses ranging from 25 to 150 mg/day, after 12 weeks of treatment [31, 33]. No definitive conclusion can be made on doses required for a positive effect since this may depend on the outcome assessed and study population.

In all studies, expect for one that used plant extracts [37], purified CBD was administered. Data derived from pre-clinical animal models indicate that purified CBD may have a bell shape response [47] which was also confirmed in two studies included in this review [25, 26]. It is likely that the use of a single cannabinoid may be inferior to the extract where other components synergize with CBD to obtain the desired effect, known as the “entourage effect” [48]. Further, the main route of administration for the studies included in this review was oral (either in the form of capsules or sublingual oil). Animal studies suggest that oral bioavailability is low [48]; on the other hand, as highlighted in a recent systematic review on the pharmacokinetics of the CBD in humans [49], there is a lack of data in humans [50].

We used the Cochrane risk of bias tool to assess the included RCTs [8]. Overall, several methodological weaknesses were identified, e.g. selective outcome reporting, inadequate randomization and blinding. Further, sample sizes were very small in most studies significantly decreasing strength of detecting differences between study groups. An important finding of this review is the heterogeneous use of doses, dosage schemes and formulations (inhalation, oral capsules and sublingual oil, topical gel) across all indications of CBD. This has several implications. Besides excluding the option of pooling data for a meta-analysis to evaluate efficacy, the consequence of non-consensus of CBD dose is important when evaluating safety issues. Commercially, several online “dose-calculators” are available for dose recommendations (e.g.; the data to support such calculators remain unclear on appropriate doses for efficacy although it seems reasonable to guide patients to safe dosage schemes and avoid adverse effects and gathering more data on how CBD is commonly being applied [51].

Although this review followed the recommendations for rigorous systematic reviews, it bears limitations here amongst a language and date restriction applied as well as a search strategy limited to electronic databases. However unlikely, other studies may not have been identified which can limit the applicability of the findings. Most of the disorders/diseases were only evaluated in single studies providing limited experience and no option to pool data, and some studies failed to present specific inclusion criteria meaning no restriction as to study group. The studies identified that evaluated identical conditions, regrettably employed different endpoints or tools of assessment.

RCTs are needed to confirm the effect of CBD on skin disorders, epilepsy and ADR following HPV vaccine. In addition, large and robust RTCs are needed to confirm the effects of CBD particularly on anxiety and psychosis. Studies should adhere to reporting standards for trials and use similar outcomes, standard measurements/tools to assess outcomes, and comparable treatment regimens to allow comparisons in future review studies. International guidelines should be implemented before the justification of further trials.


Studies included in this review evaluated mainly oral administration of purified CBD with placebo group as a comparator. However, there was larger heterogeneity between studies with regard to the population, schemes and doses of CBD, outcomes and tool of measurement. There is some evidence, even though low quality, that supports anxiolytic effect of acute administration of oral CBD. There is moderate-quality evidence that chronic and acute administration of CBD can improve psychotic symptoms in schizophrenia patients. Further, large RCTs are needed to confirm the effect of CBD for the treatment of Crohn’s disease, ulcerative colitis, dyslipidemia and cannabis use disorders. Insufficient data regarding safety issues were provided, but most studies reported no AEs with acute administration and mild to moderate adverse effects with chronic administration.

How Much CBD Oil Should I Take?

One of the most common complaints we hear about CBD is not that doesn’t work, but that figuring out the right dose can be a real pain. So we created a CBD dosage calculator that figures it all out for you and makes dosing incredibly easy. Make sure that when you are entering in your information that you only enter numbers. If you enter letters (oz, mg, lbs), then you will not get a reading and it will say Naan.

Our calculator will show you:
  • Your suggested minimum, average, and maximum daily dose based on your weight.
  • How much CBD is in a single drop and how many drops you’ll need for the above doses.
  • The concentration of your CBD bottle and how many drops your bottle has in total.
All you need is three easy to find numbers, and in three steps you’ll be on your way:
  • The first step is to input the size of your bottle in ml.
  • Second step you’ll want to enter the total mg of CBD that is in the bottle.
  • Last, you’ll need to enter your weight.

If you’re not sure what your weight is, that’s completely fine as long as you have a general guesstimate and preferably are using full spectrum CBD oil.

Dosing with full spectrum CBD oil allows you to work within a ballpark, so even when your dosage is off, you’re still rewarded with numerous therapeutic benefits.

Welcome to better health with CBD oil.

What dosing with CBD looks like?

There are so many ways people use CBD, and much of it comes down to personal preference and experimenting around to find what best works.

You can apply CBD in a number of ways, with different dosages for different medical conditions and it can really make your head spin. So let’s break it down in simple steps.

Use these steps as jumping-off points and feel free to customize any step for better CBD therapy. How much CBD you take and when, really comes down to what works best for you.

If that’s 5 mg for preventive health, that’s wonderful. If it’s 30 mg multiple times a day, that’s just as awesome.

Step 1. If you’ve never used CBD before try our Full Spectrum PurCBD+ Oil . This form offers a few extra benefits and makes up the bases for most other forms of CBD.

Step 2. Use our CBD dosage calculator and start in low dosing tier once or twice a day for the first week. Low tier = 0.022mg/lb or

Step 3. After week 1, feel free to increase your dose as needed. You can experiment by doubling or tripling your first-week dosage. You’ll likely find a certain amount were taking more CBD doesn’t really help that much more.

Pretty simple right! We recommend the oil form for first timers because when you hold it on or under your tongue for 30-60 seconds, you greatly speed up the rate when effects are felt.

This is great for judging how CBD is working for you. Plus, you can slowly increase your dose in small increments.

We always recommend using our CBD dosage calculator whenever changing your CBD dosage.

However, we don’t recommend this because of the dangers associated with high dosages.

Instead, we find that most people like having a few different dosages that they take depending on the severity of their medical condition on any given day.

For example, they may take a 15 mg CBD dosage for anxiety to help prevent it. However, if they are experiencing an anxiety attack, they may use 30 mg or more.

What happens if you take too much CBD?

The most likely thing that will happen is just a more potent and relaxing CBD session. There is a good chance you may feel tired if you go over 100 mg, but this isn’t a guarantee, and no harm comes from this side effect.

If your body isn’t used to taking CBD, throwing a lot at it can make your stomach upset. This is a normal biological response whenever something foreign enters the body the first few times, and once the stomach realizes CBD isn’t an irritant, nausea should pass.

CBD is a known inhibitor of CYP450 enzymes

This is the one side effect of concern and it only applies when taking a prescription drug metabolized in the liver. CBD inhibits CYP450 enzymes. Kale and turmeric can inhibit these same enzymes, along with grapefruit , red wine, and St John’s Wort.

When you inhibit CYP enzymes, you risk delaying the breakdown of drugs metabolized in the liver — about 50% of prescription pharmaceutical. By delaying their breakdown you raise their potency.

This is the one side effect of concern, and it only applies when taking a hepatic drug (metabolized in the liver).

How much CBD for anxiety, pain, epilepsy, and more?

This is one of the most asked questions we get, and we have an easy answer.

After your first week using a low tier dose of CBD, you’ll have a much better idea of how CBD works and feels. From here, many with chronic health conditions will jump up to a medium tier dosage and find that it equally helps with their anxiety, inflammation, appetite, etc. A generic average dose is 15-30 mg a day.

If you’re looking to treat chronic insomnia that isn’t related to external sleep disturbances — like pain, mood, etc. — a strong tier dose is recommended.

For the average person, this is anywhere over 100 mg — if you describe yourself as petite or are on the shorter/skinner side, you may feel tired with doses lower than 100 mg.

Remember, unless you’re on dosage sensitive drug metabolized by CYP enzymes, you will likely not run into any side effects even when taking several hundred milligrams of CBD a day.

Does dosing change when using different versions of CBD?

Yes, and no. The amount of CBD you find works best for you will likely not change when jumping between tinctures, capsules, or edibles.

The tincture can absorb into the bloodstream through the mucous membrane of the mouth — this greatly speeds up CBD start time and looks like it increases its bioavailability.

The former advantage is why many go with tinctures. The latter works in principle, but most people don’t seem to notice an issue with their dosage when changing to a version that passes through the digestive tract first like capsules.

When it comes to choosing which CBD is right for you, it really comes down more to personal preference. So let’s see which of our CBDs works best for your needs.

Choosing Which CBD is Right For You

Tinctures ( Full Spectrum PurCBD+ & PurCBD+ Isolate )

If you want precision dosing and fast relief, you want the original and standard CBD oil. You may feel CBD working with 5-20 minutes, and you can easily dose at whatever amount you prefer — be it 1 mg or 73 mg.

Full Spectrum: Right off the bat, if you’ve never used CBD before and don’t consider yourself a very picky eater we recommend Full Spectrum PurCBD+.

Full spectrum dosing works like climbing stairs — take more, and you’ll feel more. With the next form, you have to hit within a dosing window, which is unique to you and this takes trial and error.

We offer our Full Spectrum PurCBD+ in three different concentration sizes, and our CBD oil dosage calculator will help point you in the right direction. If you’re looking for just a bit of CBD go for a smaller size.

If you need to take a lot, grab a more concentrated version so you’re not consuming a lot of oil. Here is a chart to see how CBD is in each version.

How many mg in a drop of CBD:

  • PurCBD 250 MG: 1 drop = 0.18 mg CBD
  • PurCBD 750 MG: 1 drop = 0.54 mg CBD
  • PurCBD 1500 MG: 1 drop = 1.08 mg CBD

Nano-enhanced CBD Isolate: U nlike full spectrum, CBD isolate doesn’t have the other molecules found in hemp that increase CBD’s bio-absorption.

We’ve nano-enhanced our CBD Isolate oil to improve CBD’s absorption in the body so unlike other isolates you have a much better chance at feeling CBD’s full effects.

It can still be tricky so we suggest full spectrum first because as long as you take enough, you’ll always feel it helping.

However, in rare cases, some people feel tired with full spectrum CBD at even with lower doses — the thought is they are more sensitive to one of the other phytocannabinoids in full spectrum.

Isolate provides you with two ways to avoid this:

  • First, you can just take CBD isolate on its own which is only CBD.
  • Second, you can boost the ratio of CBD to other cannabinoids by taking both isolate and full spectrum together.
Capsules (PurHemp Gold Extra Strength)

If you hate the taste of oils, capsules offer a great way for you to still enjoy CBD. Their biggest pro is they are flavorless and easy to take. A disadvantage is capsules will offer a one-size-fits-all dose at 15 mg per capsules.

But a majority of people don’t mind this at all and many find 15 mg and 30 mg perfect amounts for both mild and severe chronic conditions, respectively. In fact, this is why you see most CBD capsules on the market contain 15 mg a piece.

In our opinion, the only big negative is they can take up to an hour before providing relief. However, with an empty stomach, effects can be felt in just 30 minutes.

This is just like taking an over-the-counter medication in pill form, so most have no issues waiting up to an hour.

Topicals (CBD Skin Care)

Here’s where you can pretty much forget about how much CBD to take. Topicals will directly target the area they are applied to, and relief can happen within 10-20 minutes. Simply apply more CBD cream if needed.

How to find the proper CBD dosage for you, according to medical cannabis experts

CBD is one of more than 60 active compounds found in the cannabis plant. It’s used to treat childhood epilepsy, but is also being studied as a way to manage and treat conditions including anxiety, schizophrenia, diabetes , Parkinson’s disease, and multiple sclerosis.

However, how much CBD you need for these conditions, or otherwise, is unclear. That’s because CBD is not regulated by the FDA and therefore lacks any official dosing guidelines.

That said, preliminary research provides a basic understanding of how much CBD can be effective for certain conditions and groups of people. Here’s what researchers know so far about CBD’s dosage and effects.

Important: Unlike THC — another common compound in marijuana — CBD is non-intoxicating and won’t make you feel “high.”

How to determine CBD dosage?

How much CBD you should take depends on multiple factors like body weight and genetics. Usually finding the right dose comes down to good, old-fashioned trial and error.

However, before experimenting with different CBD doses, you should talk to your doctor since there are no regulated dosing guidelines. Plus, studies on CBD’s effects include a wide range of doses, from “lower” doses of 10mg to 100 mg to “higher” doses of 100 mg to 1,500 mg, making it even more difficult to determine the proper dose on your own, says Anthony Ferrari, PhD, the Chief Science Officer of Your CBD Store, a nationwide CBD retail and research company.

How much CBD is in a drop of CBD oil? CBD oil typically comes in dropper bottles with a single drop containing about 0.05 ml. A product’s packaging will tell you how much CBD is in the bottle, which can help you determine how much CBD is in a single drop. For example, if a 20 ml bottle containing 2,000 mg of CBD contains 400 drops, then each drop would contain around 5 mg of CBD.

Further muddling the dosing equation is the fact that some CBD products, known as isolates, contain only CBD, while others are “full-spectrum” and contain other cannabinoids, like THC. The additional cannabinoids in full-spectrum formulas might modulate CBD’s effects, thus altering how much you need to take, Ferrari says.

Factors that influence how much CBD you should take include:

  • Bodyweight: Studies examining CBD’s effects use different doses depending on their body weight. These doses typically range from 5 to 20 mg per kilogram of body weight.
  • The condition being treated: “The clinical trial data as it stands usually suggests a lower dosage for ailments such as anxiety and a higher dosage for ailments such as sleep, chronic pain, and epilepsy,” Ferrari says.
  • Your individual body chemistry: Individuals respond differently to varying dosages of CBD due to their individual genetics and brain chemistry, says Jordan Tishler, MD, president of the Association of Cannabis Specialists and CEO of medical cannabis practice inahleMD. For example, a dose that might make one person feel slightly drowsy might cause unmanageable fatigue in another.

CBD dosage based on conditions

Clinical trials on CBD are limited and existing studies use a wide range of doses to treat various conditions. Here’s what we know so far:


Studies examining CBD’s effects on anxiety use varying doses, typically ranging from 400 mg to 600 mg per day. In a small 2017 study, test subjects reported reduced anxiety after taking a 300 mg dose of CBD.


In a couple of small studies, CBD doses ranging from 600 mg to 1500 mg per day were shown to reduce some symptoms of psychosis due to schizophrenia.

Can you take too much CBD?

CBD is generally considered to be safe and well-tolerated in doses up to 1500mg per day. While there’s a real risk of fatal overdose when using drugs like opiates or alcohol, taking too much CBD is more likely to result in sleepiness and perhaps an upset stomach.

Side effects are typically mild and include:

  • Dry mouth
  • Drowsiness
  • Diarrhea
  • Nausea

In rare instances, CBD could cause liver damage. A 2019 animal study found that liver damage occurred when mice were given high doses of CBD — the human equivalent of 200 mg of CBD per kilogram of body weight. It’s not clear if these findings are applicable to humans.

“If you are pregnant, breastfeeding, or taking any other medications, you should discuss your CBD journey with a primary care physician, Ferrari says. “Everyone experiences the effects of CBD differently and you should always monitor your body’s reactions.”

Warning: Taking CBD in addition to other medications that cause drowsiness — like benzodiazepines, antipsychotics, antidepressants, antihistamines, or alcohol — may lead to increased drowsiness, accidental falls, or accidents while driving.

Insider’s takeaway

Emerging research suggests CBD is a promising and low-risk treatment for a number of conditions — but like all medications, you need to be cognizant of dose. Because there are no regulated dosing guidelines, it’s especially important to talk to your doctor before starting a CBD regime.

“Maintaining open communication with your physician is the key to overall success when first incorporating CBD into your routine, especially for those with complicated health issues,” Ferrari says.