The causes of substance abuse are multiple. Some people are at high risk for dependence due to genetic or physiological factors. Researchers have found the sons of alcoholics to be twice as prone to alcoholism as other people. Among pairs of identical twins, if one is an alcoholic, there is a 60 percent chance that the other will be also. In spite of an apparent inherited tendency toward alcoholism, the fact that the majority of people with alcoholic parents do not become alcoholics themselves demonstrates the influence of psychosocial factors, including personality factors and a variety of environmentalstressors, such as occupational or marital problems.
Variations in the incidence of alcoholism among different ethnic groups show that social learning also plays a role in addiction. Parental influence, especially in terms of modeling the use of alcohol and other drugs, has a strong influence on the behavior of children and adolescents, as does peer behavior.
Although positive experiences with one drug may lead to experimentation with another, the “stepping stone” theory of drug use— for example, using marijuana leads to the use of hard drugs—is highly speculative as the majority of marijuana smokers do not go on to use other drugs. Only heavy marijuana use has been linked to the use of other drugs.
Taken from : The Gale Encyclopedia Of Psychology 2ND Edition - Bonnie Strickland