Marijuana has been used for thousands of years for its intoxicating effects. Marijuana was first made illegal in the United States in 1937, and the federal government made exaggerated claims about its dangers. Marijuana was described at that time as an "evil weed" that leads to violence, rape, murder, and madness. The truth is that no such connection exists for marijuana. In fact, drinking alcohol is much more likely to increase aggressive behavior and contribute to violent crime.

Marijuana is a depressant that slows down the activity of the brain and other parts of the nervous system. This inhibitory action has a relaxing or calming effect that causes people to feel "high". In very rare cases, marijuana may also cause hallucinations, which are imagined experiences that seem real.

People generally use marijuana because it makes them

• feel relaxed, happy, and at peace with the world
• giggly and talkative
• experience a heightened sense of touch, taste, and other senses

Other behaviors produced by marijuana include

• feeling that the passage of time has slowed
• increased appetite ("getting the munchies")
• drowsiness
• loss of coordination
• short-term memory loss
• difficulties in thinking, problem solving, and learning
• anxiety and panic in some people

Effects on the body: The physical effects of marijuana on the body include

• fast heart rate
• bloodshot eyes
• enlarged (dilated) pupils
• dry mouth and throat

Common street names: Pot, weed, grass, dope, tree, reefer, herb, cannabis, blunt, mary jane, and ganja.

How is marijuana used? Marijuana is most commonly smoked in a cigarette ("joint") or water pipe ("bong"). The smoke has a distinctive, slightly sweet smell that is quite different from cigarette smoke. Marijuana can also be eaten in food, such as cookies or cakes.

Risk of addiction: Low (however, smoking marijuana can become a habit that is hard to break)

Overdose: The risk of overdosing on marijuana is small and does not pose any serious physical risks, although people can become anxious and paranoid. The best way to calm such a person is through a reassuring "talk down" from someone who understands the effects of marijuana. The loss of coordination and impaired reactions caused by marijuana make it dangerous to drive a car.

How is marijuana produced? Marijuana is a natural drug consisting of dried and chopped leaves of the hemp plant (Latin name, Cannabis sativa). The active ingredient in marijuana is THC (tetrahydrocannabinol). Hashish or "hash" is the dried caked resin obtained from flowers and leaves of the female plant. It contains a higher THC concentration than marijuana and therefore tends to be stronger. Hash is sold in small chunks that range in color from light brown to nearly black.

Can marijuana be used legally? Marijuana was once prescribed frequently by doctors and is still used for medical purposes in many countries. Although it is not legal in the United States, a growing number of professionals support the medical use of marijuana for people with cancer, migraine headaches, AIDS, anorexia, glaucoma, multiple sclerosis, epilepsy, and other illnesses. Voters in several states have voted to legalize marijuana for such medical purposes, but doctors and patients still risk prosecution if marijuana is prescribed and used for treating illnesses.

THC, the active ingredient of marijuana, is legally available in a prescription drug called Marinol. Doctors prescribe Marinol for two main purposes:

• to stimulate appetite (primarily for people with AIDS or those who have had certain types of stomach surgery)
• to reduce nausea (primarily for cancer patients being treated with anti-cancer drugs that cause severe nausea and loss of appetite)

How quickly and how long does marijuana act? The effects of smoking marijuana are generally felt within a few minutes and persist for several hours. The effects of eating marijuana take longer to be felt and last longer.

Drug tests for marijuana: THC and related molecules can be detected in the urine starting at about 6 hours after smoking marijuana. These molecules continue to be found in the urine for one to several weeks, depending on how much marijuana has been smoked. In heavy marijuana users, THC can be detected for up to two months after their last use of the drug.

How many students use marijuana? About 32% of high school seniors say they have used marijuana within the past year.