The latest in NIDA's Research Report series is "Marijuana Abuse," an eight-page pamphlet that summarizes current scientific knowledge of marijuana and its effects. "Today's marijuana is far more potent than the marijuana of 30 years ago," says NIDA Acting Director Dr. Glen R. Hanson. "The drug can produce a range of adverse physical and emotional effects, and -- contrary to what many people believe -- it can be addictive."

Acute Effects of Marijuana Use

Marijuana's effects start as soon as the drug enters the brain. The drug's mind-altering effects are caused by tetrahydrocannabinol (THC). Just a few minutes after inhalation of marijuana smoke, the user's heart rate accelerates, bronchial passages relax, and blood vessels in the eyes enlarge. Soon the user feels euphoric, experiencing pleasant sensations, colors, and sounds more intensely than usual. He or she may develop a dry mouth and feel very hungry or thirsty. When the euphoria passes, the user may feel sleepy or depressed. Sometimes marijuana use produces anxiety, fear, or panic in the wake of euphoria.

During marijuana intoxication, a user may have difficulty forming memories. THC also interferes with parts of the brain that control balance, posture, and coordination of movement.

With high doses of marijuana, the user may suffer toxic psychosis, including hallucinations, delusions, and a loss of the sense of personal identity. The specific causes are unknown, but toxic effects are more likely when a strong dose of THC is consumed in food or drink rather than smoked.

Long-Term Effects On Health

Marijuana has negative effects on memory and learning skills that are persistent but may not be permanent. Other effects of long-term abuse are cumulative and may last indefinitely. Regular marijuana smokers may have many of the same respiratory problems that tobacco smokers do: daily cough and phlegm production, frequent respiratory illness, a tendency toward obstructed airways, and a heightened risk of lung infections. Data suggest also that marijuana smoke increases the likelihood that head and neck cancers will develop, and it has the potential to promote lung cancer.

Some adverse effects may result from THC's impairing the immune system. In studies with mice, those exposed to THC or related substances were more likely than the unexposed animals to develop bacterial infections and tumors. In studies that used both animal and human cells exposed to marijuana ingredients, the normal disease-preventing actions of immune cells were inhibited.

A serious risk of long-term marijuana use is addiction -- compulsive use of the drug, even though it interferes with family, school, and work. Withdrawal symptoms and drug craving can make it hard for long-term marijuana users to stop the drug. There are no medications to treat marijuana addiction, but behavioral therapies are available. Researchers are focusing on the most effective forms of counseling and incentives for abstinence.

Effects on School, Work, and Social Life

Students who smoke marijuana get lower grades than those who don't. Workers who smoke it are more likely to have problems on the job. Depression, anxiety, and personality disturbances are all associated with marijuana use. Marijuana interferes with a person's ability to learn and remember information, so frequent users may fall behind in developing intellectual, job, or social skills. Research with students has shown that marijuana use is linked to a reduction in the psychological skills that enable individuals to maintain confidence and persist in their pursuit of goals.

For More Information

"Marijuana Abuse" can be ordered from the National Clearinghouse for Alcohol and Drug Information; call 800-729-6686 (800-487-4889 for the deaf) or order online at ncadi.samhsa.gov. Ask for publication #PHD940.

Further information about marijuana use and consequences can be found at NIDA's Web site, www.drugabuse.gov, and the new companion site, marijuana-info.org.

Volume 17, Number 3 (October 2002)