After about 25 years old, few people begin such behaviours. However, once established, most drug users continue to use their drug of choice for the rest of their lives or until detrimental effects occur. Drinking, drug-use and smoking are, then, largely social activities, as they always have been. Norms are socially derived, serve to locate people within groups and control the interactions between them. Social contexts largely drive group behaviours.
Studies repeatedly show peer pressure as the major influence on uptake of drug use.