Medical marijuana may be:

• Smoked
• Vaporized
• Eaten
• Taken as a liquid extract

Marijuana leaves and buds contain substances called cannabinoids. THC is a cannabinoid that can affect the brain and change your mood or consciousness.

Different varieties of marijuana contain different amounts of cannabinoids. This sometimes makes the effects of medical marijuana hard to predict or control. The effects also may differ depending on whether it is smoked or eaten.

Medical marijuana may be used to:

• Ease pain. This includes different types of chronic pain, including pain from nerve damage.
• Control nausea and vomiting. The most common use is for nausea and vomiting caused by chemotherapy for cancer.
• Make a person feel like eating. This helps people who do not eat enough and lose weight due to other illnesses, such as HIV/AIDS and cancer.

Some small studies show that marijuana might relieve symptoms in people who have:

• Multiple sclerosis
• Crohn disease
• Inflammatory bowel disease
• Epilepsy

Smoking marijuana lowers pressure inside the eyes. But the effect does not last long and this is not often the recommended treatment for glaucoma. Other glaucoma medicines work better to treat the disease.

In states where medical marijuana is legal, you need a written statement from your health care provider to get the drug. It must explain that you need it to treat a medical condition or to ease side effects. Your name will be put on a list that lets you buy marijuana from an authorized seller.

You can only get medical marijuana if you have certain conditions. The conditions marijuana can be used to treat vary from state to state. The most common ones include:

• Cancer
• HIV/AIDS
• Seizures and epilepsy
• Glaucoma
• Severe chronic pain
• Severe nausea
• Extreme weight loss and weakness (wasting syndrome)
• Severe muscle spasms
• Multiple sclerosis

Possible physical symptoms from using marijuana include:

• A fast or irregular heartbeat
• Dizziness
• Slow reaction times
• Drowsiness

Possible mental or emotional side effects include:

• A strong feeling of happiness or well-being
• Short-term memory loss
• Trouble concentrating
• Confusion
• Decreased or increased anxiety

Providers are not allowed to prescribe medical marijuana to people younger than age 18. Other people who should not use medical marijuana include:

• People with heart disease
• Pregnant women
• People with a history of psychosis

Other concerns linked to marijuana use include:

• Dangerous driving or other risky behaviors
• Lung irritation
• Dependence or addiction to marijuana

The US Food and Drug Administration (FDA) has not approved marijuana for treating any health conditions.

However, the FDA has approved two prescription medicines that contain man-made cannabinoids.

• Dronabinol (Marinol). This drug treats nausea and vomiting caused by chemotherapy and loss of appetite and weight loss in people with HIV/AIDS.
• Nabilone (Cesamet). This drug treats nausea and vomiting caused by chemotherapy in people who have not had relief from other treatments.

Unlike medical marijuana, the active ingredient in these drugs can be controlled, so you always know how much you get in a dose.

Pot; Grass; Cannabis; Weed; Hash; Ganja

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Updated by: Linda J. Vorvick, MD, Clinical Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.