For our purposes, we define addiction as compulsive use o fa drug accompanied by signs of physiological dependence
By physiological dependence, we mean that a person’s body has changed as a result of the regular use of a psychoactive drug in such a way that it comes to depend on having a steady supply of the substance.

Depressants
A depressant is a drug that slows down or curbs the activity of the central nervous system. It reduces feelings of tension and anxiety, slows movement, and impairs cognitive processes. In high doses, depressants can arrest vital functions and cause death.
The most widely used depressant, alcohol, can cause death when taken in large amounts because of its depressant effects on breathing. Other effects are specific to the particular kind of depressant. For example, some depressants, such as heroin, produce a “rush” of pleasure. Here let us consider several major types of depressants.
The most widely used depressant, alcohol, can cause death when taken in large amounts because of its depressant effects on breathing. Other effects are specific to the particular kind of depressant. For example, some depressants, such as heroin, produce a “rush” of pleasure. Here let us consider several major types of depressants.
Barbiturates
About 1% of adult Americans develop a substance abuse or dependence disorder involving the use of barbiturates, sleep medication (hypnotics),or anti anxiety agents at some point in their lives. Barbiturates such as amobarbital, pentobarbital, pheno-barbital, and secobarbital are depressants, or sedatives. These drugs have several medical uses, including easing anxiety and tension, dulling pain, and treating epilepsy and high blood pressure. Barbiturate use quickly leads to psychological dependence and physiological dependence in the form of both tolerance and development of a withdrawal syndrome.