Marihuana has been used by man in countries around the world for many centuries. Scientifically, more is known about marihuana's effects than many other botanical substances consumed by man.

Marihuana is one of several preparations from the plant, cannabis sativa. The plant contains many different chemicals, but tetrahydrocannabinol appears to be the major active psychopharmacologic ingredient. The potency of the preparation is determined by the THC content, which varies according to the origin of the seed, the conditions of cultivation, and the extent of manicuring.

Several important factors exert significant influences on the psychopharmacological effect. These include dose, method of use, set and setting, and pattern of use including frequency and duration of use.

The acute subjective experience is dose-dependent. At low doses commonly used in this country a mild intoxication occurs, but at higher doses psychotomimetic experiences can occur. Few consistent physiological effects are noted. No pathologic bodily changes have been conclusively demon, strafed from acute use. Subtle effects on recent memory, psychomotor function, and social behavior have been demonstrated.

The margins of safety between the effective dose and the toxic dose is quite large. No human fatalities have been noted in this country caused by marihuana. The most common adverse reactions are becoming too intoxicated, and the acute anxiety panic reaction. Both of these are transient and related to dose consumed as well as set and setting factors.

Acute psychotic, reactions are quite rare. They usually last a few days to weeks and occur in predisposed persons either with preexisting mental disorders or borderline personalities especially under stressful conditions. Transient acute brain syndrome or toxic psychosis is possible at extremely large doses.

Evidence has accumulated which indicates that differential tolerance does develop at least, in persons who smoke large amounts of marihuana several times a day. Development of tolerance to the depressant effects on behavior appears to precede development of tolerance to the intoxicant effect.

Physical dependence has not been demonstrated. Little, if any, psychological dependence is present in most intermittent marihuana users. Moderate psychological dependence occurs in moderate to heavy users and marked psychological dependence has been described in very heavy chronic users.

Some detrimental effects have been conclusively linked to short- and long-term marihuana use for very heavy users. The most frequently reported change in the heavy, long-term smokers of large quantities of potent preparations is chronic bronchitis comparable to that developed by a heavy, long-term tobacco cigarette smoker. A chronic cannabis psychosis probably occurs rarely in heavy chronic, hashish smokers in Eastern countries. Most psychotic episodes are the acute variety and clear in a few days to weeks. No objective evidence has been demonstrated that even very heavy, long-term hashish use causes organic brain damage.

Objective studies of chronic, heavy smokers of potent preparations have not causally linked this drug with the amotivational syndrome which has been described by many clinicians. Almost all chronic, heavy hashish smokers are indistinguishable from their peers in the lower socioeconomic strata of their respective societies in social behavior, work performance, mental status and overall life style.