
Psychoactive drugs are substances that alter the mental state of humans after ingestion. There are a wide variety of those substances, both naturally occurring and synthesized, including tobacco, alcoholic beverages, coffee, tea, chocolate, and some spices, as well as substances that are legally available only through medical channels, such as benzodiazepides, cannabinols, opiates, and cocaine. Such substances often have other use values along with their psychoactive properties. Users may like the taste or the image of themselves that the use of those substances conveys. Substance use may be a medium of sociability (Partanen) or part of a religious ritual. Some substances have other useful properties; alcohol, for example, is a source of calories and is used as a solvent in many tinctures.
Psychoactive drugs differ in their metabolic pathways and mechanisms of action in the human body, the strength of their effects, and the states of mind and feelings they induce. However, the effects of drug use also are highly dependent on the pattern of use and on the set and setting, that is, the expectations of the user and of others who are present and the context of use (Zinberg). Although the psychoactive effect of tobacco may not register in the consciousness of a habituated cigarette smoker, in other circumstances the effect of tobacco use may be so strong that the user is rendered unconscious, as early Spanish observers reported in describing tobacco use among native South Americans (Robicsek).