From www.agebb.missouri.edu/occmed/bull13q.htm:
**Marijuana temporarily affects vision, hearing, judgement, memory, and sense of time. The impairment lasts longer than the feeling of being “high,” so users may try to drive or do other things when they should not. Marijuana users are more likely to be involved in fatal crashes than nonusers. Temporary effects last several days.
BEHAVIOR
Marijuana affects behavior. Heavy users are less likely to socialize, set or achieve goals. Pre-employment drug screens positive for marijuana use are linked to higher job turnover, accidents, injuries, discipline problems and absenteeism.
Marijuana users have measurable changes in their brains. These include temporary changes in the electrical brain waves, called EEG’s, and permanent brain abnormalities whose meaning is not yet understood.
In high doses or especially among people who have mental disorders, using marijuana even once may cause extreme anxiety, paranoia, or hallucinations. Mental illnesses, such as schizophrenia, may appear or worsen with marijuana use. Epileptic seizures are also linked to marijuana use.
CANCER
Marijuana smoke causes cancer. It is more carcinogenic than tobacco smoke.
REPRODUCTION AND DEVELOPMENT
Marijuana decreases sex hormones, weight of the sexual organs, and sexual appetite. Sperm of marijuana users are fewer, and are abnormal in structure and function. Women who use marijuana also have lower fertility and are more likely to have a miscarriage.
Marijuana compounds cross the placenta and affect fetal development. They also pass into a mother’s milk. Babies born to women who use marijuana may have low birth weight, physical and mental defects resembling fetal alcohol syndrome, and inadequate sex differentiation or development.
LUNGS
Marijuana smoke causes lung damage similar to cigarette smoke. However, marijuana is more harmful to lung function than tobacco cigarettes. Marijuana smoke is also far more irritating to the sinuses, throat and lungs than tobacco smoke. Marijuana smoke damages alveolar macrophages, an important part of the immune system in the lungs.
HEART AND CIRCULATORY SYSTEM
Smoking marijuana is a serious risk for people with hypertension, heart and cerebrovascular diseases. These people should not use marijuana!
DRUG DEPENDENCY
Mild physical dependence often results from marijuana use.
LEGAL ISSUES
It is illegal for most people to use, possess, grow, buy or sell marijuana. Marijuana can legally be prescribed by a physician to treat cancer patients for the nausea and poor appetite caused by chemotherapy. Other drugs are more effective, but for those unable to tolerate such drugs, marijuana or THC may be helpful. Marijuana also can help patients with glaucoma. However, other drugs usually have less harmful side effects than marijuana.
IN SUMMARY
There are good reasons not to use marijuana even once: It is dangerous for driving, can cause memory problems, may have psychotic effects, and is dangerous for people with heart or circulatory problems. Women who are pregnant or nursing should never use marijuana. Since marijuana is illegal, there is no way to guarantee that what appears to be marijuana is in fact marijuana, or in what concentration the active ingredient THC may be found.
There are good reasons to avoid chronic use of marijuana: It retards social development and motivation, learning and intellect; reduces fertility and sex drive; causes cancer, lung disease, birth defects, and miscarriages; retards growth; decreases body weight, and causes physical dependence.**