Marijuana (cannabis) use is widespread. Surveys of high school students have shown periodic variation in its use.
In the United States, marijuana is commonly smoked in the form of cigarettes (joints) made from the stems, leaves, and flowering tops of the dried plant (Cannabis sativa or Cannabis indica). Marijuana is also used as hashish, the pressed resin (tarry substance) of the plant. The active ingredient of marijuana is tetrahydrocannabinol (THC), which occurs in many variations. The most active variation is delta-9-THC. Dronabinol, a synthetic form of delta-9-THC, is used to relieve nausea and vomiting caused by chemotherapy drugs and to enhance appetite in people with AIDS.
Most people use marijuana intermittently and without developing noticeable social or psychologic dysfunction or dependence. However, some people become dependent on marijuana.
Marijuana slows brain activity, producing a dreamy state in which ideas seem disconnected and free-flowing. It is mildly psychedelic, causing time, color, and spatial perceptions to distort and be enhanced. Colors may seem brighter, sounds may seem louder, and appetite may be increased. Marijuana generally relieves tension and provides a sense of well-being. The sense of exaltation, excitement, and inner joyousness (a high) seems to be related to the setting in which the drug is taken—such as whether the smoker is alone or in a group and what the prevailing mood is. Coordination, reaction time, depth perception, and concentration may be impaired during marijuana use, so driving or operating heavy equipment is dangerous. Other effects include an increased heart rate, bloodshot eyes, and dry mouth. Effects usually last 4 to 6 hours after inhalation.
Some people, especially those who have not used marijuana before, experience anxiety or feel panicky or paranoid. If people have a psychosis (loss of contact with reality) such as schizophrenia, using marijuana may make symptoms worse or trigger new symptoms.
People who use large quantities of marijuana for a long time may develop breathing problems, such as bronchitis, wheezing, coughing, and increased phlegm. However, even daily smokers do not develop obstructive airway disease. There is no evidence of increased risk of head and neck or airway cancers, as there is with tobacco.
Pregnant women who use marijuana may have smaller babies than nonusers, but the effect seems small. Delta-9-THC passes into breast milk, but no harmful effects have been detected. Nonetheless, women who are pregnant or breastfeeding are advised not to use it.
Marijuana is eliminated from the body slowly over several weeks, so withdrawal symptoms tend to be mild. After a few weeks of heavy, frequent use, abruptly stopping causes symptoms that begin about 12 hours later and last up to 7 days. Symptoms include insomnia, irritability, depression, nausea, and loss of appetite.
Diagnosis and Treatment
A urine test can detect marijuana for several days or weeks after it is used, even in casual users. In regular users, the test may detect the drug for even longer while the drug is slowly released from body fat. Urine testing is an effective means of identifying marijuana use, but a positive result means only that a person has used marijuana. It does not prove that the user is currently impaired (intoxicated).
For people who want to stop using marijuana, counseling, behavior modification, and drug treatment programs may be helpful. However, success relies heavily on their motivation to stop and, for some users, on their willingness to disassociate from their social circle of regular users.
Last full review/revision January 2009 by Patrick G. O'Connor, MD, MPH