Marijuana is a green, brown, or gray mix of dried, crumbled leaves from the marijuana plant. It can be rolled up and smoked like a cigarette or cigar or smoked in a pipe. Sometimes people mix it in food and eat it.
Marijuana can cause problems with memory, learning, and behavior. Smoking it can cause some of the same coughing and breathing problems as smoking cigarettes. Some people get addicted to marijuana after using it for a while. It is more likely to happen if they use marijuana every day, or started using it when they were teenagers.
Some states have approved "medical marijuana" to ease symptoms of various health problems. Marijuana isn't an FDA-approved medication. THC, the active ingredient in marijuana, is approved to relieve nausea caused by cancer chemotherapy and to stimulate appetite in severe weight loss caused by AIDS. Scientists are doing more research on marijuana and its ingredients.
NIH: National Institute on Drug Abuse