Marijuana is made from the dried leaves and buds of the Cannabis sativa plant. While the Food and Drug Administration (FDA) hasn't approved the use of the marijuana plant as medicine, many states have legalized marijuana use.

The FDA has approved two drugs, dronabinol (Marinol, Syndros) and nabilone (Cesamet), made from synthetic forms of ingredients found in marijuana. They can be legally prescribed for the treatment of nausea and vomiting caused by chemotherapy when other treatments have failed. Dronabinol might also be used for the treatment of decreased appetite associated with weight loss in people with HIV and AIDS.

The FDA has also approved a liquid medication (Epidiolex) containing a purified form of cannabidiol (CBD), a chemical found in marijuana. This drug can be used for the treatment of rare forms of severe childhood epilepsy (Lennox-Gastaut syndrome and Dravet syndrome).

Medical marijuana is available as an oil, pill, vaporized liquid and nasal spray, as dried leaves and buds, and as the plant itself. The herb is typically used to treat nausea and vomiting associated with cancer treatment, loss of appetite and weight loss associated with HIV/AIDS, epilepsy, chronic pain and muscle spasms.

Research on the use of marijuana for specific conditions shows:

• Glaucoma. Marijuana might reduce the pressure in the eye caused by this eye condition. However, the effect appears to last only a few hours. Some findings indicate that marijuana may decrease blood flow to the optic nerve, increasing the risk for vision loss in people with glaucoma.
• Nausea and vomiting associated with cancer treatment. Research has shown that an active ingredient in marijuana, tetrahydrocannabinol (THC), effectively reduces nausea and vomiting in people undergoing chemotherapy.
• Pain. Marijuana use might reduce the intensity of shooting or burning pain often due to nerve damage (neuropathic pain) caused by HIV, diabetes and other conditions.
• Seizures. It's not clear if marijuana effectively treats seizures.
• Spasticity. Marijuana use might reduce muscle stiffness or spasms and urinary frequency caused by multiple sclerosis.

Medical marijuana use is generally considered safe. But different strains of marijuana have different amounts of THC. This can make dosing marijuana difficult.

Marijuana can cause:

• Headaches
• Dry mouth and dry eyes
• Lightheadedness and dizziness
• Drowsiness
• Fatigue

Other side effects may include:

• Nausea and vomiting
• Disorientation
• Hallucinations
• Increased heart rate
• Increased appetite

Marijuana use impairs attention, judgement and coordination. Don't drive or operate machinery when using marijuana.

If you have a mental health condition, use marijuana with caution. Marijuana use might worsen manic symptoms in people who have bipolar disorder. If used frequently, marijuana might increase the risk of depression or worsen depression symptoms. Research suggests that marijuana use increases the risk of psychosis in people who have schizophrenia.

Smoking marijuana can affect your memory and cognitive function and cause harmful cardiovascular effects, such as high blood pressure. Long-term marijuana use can worsen respiratory conditions.

Marijuana has a central nervous system (CNS) depressant effect. As a result, marijuana use in combination with anesthesia or other drugs used during or after surgery might cause an additive effect. Don't use marijuana two weeks before planned surgery.

Possible interactions include:

• Alcohol. Marijuana use might increase the effects of alcohol.
• Anticoagulants and anti-platelet drugs, herbs and supplements. These types of drugs, herbs and supplements reduce blood clotting. Marijuana might change how the body processes them, possibly increasing the risk of bleeding.
• CNS depressants. Marijuana use in combination with CNS depressants might increase the sedative effect of these drugs.
• Protease inhibitors. When used with these antiviral drugs, marijuana might reduce their effectiveness.
• Selective serotonin reuptake inhibitors. Mixing marijuana with this type of antidepressant might increase the risk of mania.