One way to look at drug use is as a social disease. You contract drug use from some user. You wantto be like them or be in their social circle. You have a couple of drinks, or smoke a marijuana cigarette, or snort some cocaine, not only to get high, and sometimes not even to get high, but to socialize, to share with a friend, or make a new friend. This is where most drug use starts, and sharing and socializing remain a feature of almost all drug use.
Ignorance is another big factor in the starting of drug use.
Not knowing the dangers of drugs leads to an uninformed decision to use drugs. In recent times, Perhaps the largest contributer to the increase of drug use is their illegality. The person who is rebellious or angry at society will express these feelings by defying the law and using drugs. This defiance has generated a lot of drug use out of the alienation many disenfranchised people feel. Why Prohibitions Fail.