The previous section has attempted to paint a broad picture of the marihuana user. This section will deal with the, drug and its effects on these individuals.

The meaning of drug often varies with the context in which it is used. The physician would define a drug as any substance used as a medicine in the treatment of physical or mental disease. Today, due to the influence of many factors, the layman may focus on the negative connotations of drugs, such as the stupefying, poisoning, habit-forming misuse of the opiate drugs. The considerably wider and more scientific definition of a drug which will be used in this section is: any chemical substance which has an action on living tissues.

A psychoactive drug is any substance capable of modifying mental performance and individual behavior by inducing functional or pathological changes in the central nervous system.
is any substance capable of modifying mental performance and individual behavior by inducing functional or pathological changes in the central nervous system.

As defined, psychoactive drugs exert their major effect on the state of the mind including emotions, feelings, sensibility, consciousness and thinking. The definition implies neither positive nor negative meanings. Chemical substances are not inherently good or bad. All substances, including medicines and foods, which man has chosen to consume have certain desired effects (whether therapeutically beneficial or pleasurable) and undesired effects (whether detrimental or unpleasant). For example, eating food is certainly a necessary and pleasurable activity. However, obesity plays an important role in many diseases, including diabetes, high blood pressure and heart attacks, and tends to limit physical activities.

The classification of any drug effect as either beneficial or harmful often greatly depends on the values the classifier places on the expected effects. This is especially relevant with respect to the psychoactive drugs such as tranquilizers, stimulants, coffee, cigarettes, alcohol, marihuana and other licit or illicit drugs. For all of these drugs, the weights of benefit and harm are difficult to determine when viewed merely in terms of their stated effects.