How Marijuana Affects Your Body
Let’s be honest: This is why most people use marijuana. THC is what causes the high. When you smoke marijuana, THC goes from your lungs to your bloodstream and then makes its way to your brain. There it connects to parts of certain cells called receptors. That’s what gives you those pleasant feelings. You can also get marijuana in things like cookies, gummies, and brownies. These are called edibles. They get into your blood through your digestive system.
You might find it harder to focus, learn, and remember things when you use marijuana. This short-term effect can last up to 24 hours after you stop smoking. Long-term use, especially in your teens, may have more permanent effects. Imaging tests that take pictures of the brain show fewer connections in areas linked to alertness, learning, and memory. Tests show lower IQ scores in some people.
Marijuana smoke can inflame your lungs. If you’re a regular user, you could have the same breathing problems as a cigarette smoker. That means a cough, sometimes long lasting, or chronic. It might produce colored mucus, or phlegm. You could also be more likely to get lung infections. Inflamed lung tissue is part of the reason, but THC also seems to affect the way some people’s immune systems work.
Your normal heart rate of 50 to 70 beats per minute can rise by 20 to 50 beats or more for up to 3 hours after you use marijuana. Scientists think that this, along with tar and other chemicals in the drug, may raise your chance of a heart attack or stroke. The risk could go up further if you’re older or you already have heart problems.
Anxiety and paranoia are common complaints among marijuana users. Clinical anxiety and depression are also more likely, but scientists aren’t yet sure exactly why. The drug can make symptoms of more serious mental illness like psychosis and schizophrenia worse. It’s also linked to a higher likelihood of substance abuse. These effects could be worse if your genes make you more likely to get a mental illness or an addiction.
Regular marijuana users often refer to this as the munchies. Some reports suggest this increased appetite might help you gain weight lost to illnesses like AIDS or cancer, or because of treatment for those diseases. Scientists are still studying when and if the treatment works or if it’s safe.
By itself, THC (marijuana’s active ingredient) seems to ease nausea, especially if your symptoms are from chemotherapy treatment for cancer. Some people say the stomach-settling effects work better when you use marijuana instead of THC alone. This may be because other chemicals enhance the effects of THC. But long-term marijuana use can have the opposite effect and cause more vomiting. Cannabinoid hyperemesis syndrome can occur in regular users and leads to frequent vomiting.
Some evidence suggests that marijuana, or chemicals in it, can lower the eye pressure that’s a main symptom of glaucoma. The problem is the effect only lasts 3 to 4 hours. To keep it low, you’d have to get the drug into your bloodstream 6-8 times a day. Doctors have yet to come up with a form of the drug that’s safe to use as a glaucoma treatment. And though marijuana does seem to lower eye pressure, it also might reduce the blood supply to your eye, which could make glaucoma worse.
Both marijuana and a pill version of THC called dronabinol seem to help relieve pain by attaching to parts of brain cells called cannabinoid receptors. Some studies suggest CBD oil could ease pain from arthritis, nerve damage (neuropathy), and muscle spasms, among other causes. Scientists continue to study how and when and if this works in people.
A version of THC that you spray up your nose called nabiximols is available in Canada, the U.K., and other countries. It seems to help calm muscle spasms, lessen nerve pain, and improve sleep for many people with multiple sclerosis. It may also help with other illnesses, like cancer. The FDA is working to test the drug for use in the U.S.
Though smoking marijuana can inflame your lungs, substances called cannabinoids seem to lessen the swelling in certain other tissues. Cannabidiol may be a good choice because it doesn’t cause the same high as THC. In animal tests, it shows some promise in the treatment of rheumatoid arthritis and conditions that inflame the digestive tract, like ulcerative colitis and Crohn’s disease.
There’s good evidence that marijuana, or drugs made from it, may help lessen seizures in some people with epilepsy. The FDA has even approved a drug made with cannabidiol for that purpose (Epidiolex). But the agency only recommends it for two rare forms of childhood epilepsy called Lennox-Gastaut syndrome and Dravet syndrome.
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1) Science Source
British National Health Service: “Cannabis: the facts.”
CDC: “Marijuana and Public Health.”
Colorado Department of Public Health: “FAQ — Health Effects of Marijuana.”
Epilepsy Currents: “Cannabidiol: Promise and Pitfalls.”
European Journal of Pain: “Transdermal cannabidiol reduces inflammation and pain-related behaviours in a rat model of arthritis.”
Glaucoma Research Foundation: “Should You Be Smoking Marijuana To Treat Your Glaucoma?”
Government of Canada Department of Public Health: “Health effects of cannabis.”
Journal of Epilepsy Research: “Cannabinoids in the Treatment of Epilepsy: Hard Evidence at Last?”
Journal of Experimental Medicine: “Cannabinoids suppress inflammatory and neuropathic pain by targeting α3 glycine receptors.”
National Cancer Institute: “Cannabis and Cannabinoids (PDQ®)–Health Professional Version.”
National Institute on Drug Abuse: “Marijuana,” “What are marijuana’s effects on lung health?”
“What are marijuana’s long-term effects on the brain?” “What is marijuana?”
Nemours Foundation: “Marijuana.”
New England Journal of Medicine: “Adverse Health Effects of Marijuana Use.”
FDA: “FDA approves first drug comprised of an active ingredient derived from marijuana to treat rare, severe forms of epilepsy.”
Reviewed by Jennifer Casarella, MD on December 17, 2021
This tool does not provide medical advice. See additional information.
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional medical advice, diagnosis or treatment and should not be relied on to make decisions about your health. Never ignore professional medical advice in seeking treatment because of something you have read on the WebMD Site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
What Is Arnica?
Cathy Wong is a nutritionist and wellness expert. Her work is regularly featured in media such as First For Women, Woman's World, and Natural Health.
Meredith Bull, ND, is a licensed naturopathic doctor with a private practice in Los Angeles, California.
Verywell / Anastasia Tretiak
Arnica is an herb. It is in the sunflower family (Asteraceae).
Several species of Arnica contain an anti-inflammatory compound. This is thought to relieve pain, aches, and bruising. It is usually applied topically to the skin. Oral forms are also available.
This article discusses arnica, its uses, side effects, and preparation. It also looks at some of the research into its effectiveness.
What Is Arnica?
Arnica comes from the sub-alpine regions of western North America. It can also be found in arctic regions of Europe, Asia, and North America.
Arnica plants have long, downy leaves. Their flowers are daisy-like. They are bright yellow or orange and between 2 and 3 inches wide.
The anti-inflammatory ingredient in arnica is called helenalin . This compound is very toxic when consumed. It can also irritate the skin if it is not diluted.
Arnica is often sold as an over-the-counter (OTC) topical ointment, gel, or cream. It is also sold as a homeopathic topical application or oral pellet. Homeopathic remedies are highly diluted.
Other forms include:
- Oral supplements
- Aromatherapy oil
- Dried "wild-crafted" herb
Arnica is an herb believed to help relieve pain. It is available in topical and oral forms. It is very toxic if not diluted.
What Is Arnica Used For?
Arnica is commonly used in alternative medicine. It is claimed to treat:
- Pain or muscle soreness or aching joints
The plant can be toxic. Because of this, it is most often used in a homeopathic form. Homeopathic products contain very small amounts of an active ingredient.
Arnica is sold by homeopathic drug makers. It is used for a number of conditions, including:
There is limited evidence to support arnica's use in treating any condition. This does not necessarily mean it does not have benefits. It just means that clinical studies have so far been small and poorly designed. Many have contradictory findings.
Talk with a doctor before deciding if arnica is a safe option for you.
Arnica is used to treat a number of conditions, including arthritis and muscle soreness. To date, there is little evidence to support its use.
Osteoarthritis is often referred to as “wear-and-tear” arthritis. In this condition, the cartilage that protects the joints wears down over time. It is often treated with nonsteroidal anti-inflammatory drugs (NSAIDs).
Arnica is thought by some to be a safe, natural alternative to NSAIDs.
In a 2013 review, Australian researchers looked at seven trials on topical herbal remedies for osteoarthritis.
Arnica gel appeared to work nearly as well as Advil (ibuprofen). Benefits included reducing pain and improving joint function in people with hand osteoarthritis.
However, 13% of those who used arnica gel had side effects. This is compared to 8% of Advil users. Some even reported an increase in joint stiffness and pain.
Post-Surgical Pain and Bruising
Proponents of arnica think it can reduce bruising and swelling after surgery. For this use, it is either applied topically or taken as an oral supplement.
A 2016 review suggested that the arnica species A. montana was a "valid alternative" to NSAIDs in treating:
- Post-operative pain or swelling or bruising
Reviewers did state, though, that the results varied based on formulation and dosage.
Another review concluded there wasn't enough evidence to support the use of oral or topical arnica for swelling or bruising after surgery.
Muscle pain is also called myalgia. It is associated with a wide range of medical conditions. It can also happen after simple overuse of the muscles.
Most studies on arnica have focused on post-exercise muscle pain. Arnica has long been used for this purpose in sports supplements. Even so, there is little evidence to support its use.
One review of studies strongly endorsed the combined use of oral and topical arnica for muscle injuries.
The authors came to this conclusion even though four studies in the review found no benefits compared to a placebo. A placebo is a substance that contains no active ingredients.
Possible Side Effects
Arnica is known to cause side effects. This is true even when used in very diluted topical ointments or creams. More serious side effects can occur with oral forms.
In less-diluted formulas, arnica may cause a mild allergic reaction. This happens most often in people allergic to plants of the Asteraceae family. These plants include:
Arnica can also trigger increases in blood pressure and heart rate. This is more likely if used in excess or on broken skin.
More of the active ingredient can be absorbed through broken skin. On broken skin, arnica may also cause stinging.
Most homeopathic arnica remedies are very diluted. These are generally considered safe. Some forms, though, may contain detectable amounts of helenalin. These forms have health risks.
When taken by mouth, helenalin can cause:
- Mouth and throat irritation
- Stomach pain
- Shortness of breath
- Easy bruising and bleeding
- Rapid heartbeat
- High blood pressure
Avoid oral preparations containing pure arnica. These are more likely to cause symptoms. They can also damage the heart and increase the risk of organ failure, coma, and death.
Contraindications and Interactions
In theory, arnica could slow blood clotting. Use of any non-homeopathic arnica should be discontinued two weeks before surgery. This will reduce the risk of postoperative bleeding.
Avoid arnica if you are taking blood-thinning drugs. The combination could increase your risk of bleeding and bruising.
These drugs include:
Little is known about the safety of arnica during pregnancy. If you are pregnant or breastfeeding, ask your doctor before using arnica in any form.
Arnica may interact with other drugs. Avoid using it if you are taking blood-thinning medication.
Verywell / Anastasiia Tretiak
Selection, Preparation, and Storage
Arnica montana is the species most often used for medical purposes. Chamissonis, A. longifolia, and A. gracilis are also sometimes used.
Most OTC arnica is very diluted. This results in gels, ointments, and extracts with little to no helenalin. This is also true for arnica powders, capsules, and other oral forms.
When purchasing arnica, look for brands that have been tested by an independent certifying body, such as:
- U.S. Pharmacopeia (USP)
- NSF International
This way, you can be sure the product label is accurate. You will also be able to tell if there is any helenalin in the product.
Also make sure the Latin name of the arnica species (such as Arnica montana) is on the product label. Be wary of any product that claims to contain "pure arnica."
Never buy dried wild-crafted arnica. Don't grow fresh arnica and use it to make teas or tonics. There is no way to safely dose arnica at home. Your exposure to helenalin is likely to be excessive, if not dangerous.
Most arnica preparations can be stored at room temperature. As a general rule, store them in their original containers. Keep them away from direct sunlight.
Never use more than the dose listed on the product label. Discard any arnica that is past its expiration date.
Arnica is an herb commonly used to treat pain. There is limited evidence to support its use.
Arnica is believed to help relieve pain associated with arthritis and muscle soreness. It is also used to treat post-surgical swelling and bruising. It is available in topical and oral forms.
When it is undiluted, arnica may cause side effects like nausea, rapid heart rate, and bruising or bleeding. It may also interact with blood-thinning drugs.
Always ask a doctor before using any natural remedy. Look for arnica that is diluted and has been tested by a third party.
A Word From Verywell
Herbal remedies aren't subject to the same regulatory standards as pharmaceutical drugs. Be cautious when using any such product. Always ask your doctor before trying any of these remedies.
Remember that even natural products can be dangerous. They may cause unwanted side effects or interact with other drugs or supplements.
Frequently Asked Questions
There is some evidence that topical arnica can treat inflammation related to osteoarthritis and swelling from injuries.
Oral arnica products have potentially toxic side effects. While some highly diluted homeopathic products may be safe, it’s best to ask your doctor before taking pills, tablets, tinctures, or oils.