In 2001, The National Institute of Justice released a report on drug epidemics and warned of a new marijuana epidemic that had begun in the 1990s. Through extensive research, the Institute discovered an alarming rise in marijuana usage among the nation’s youth. This trend could have serious implications, including precipitating an increase in so-called “hard drugs” such as cocaine and heroine, according to the idea that marijuana is a gateway to other more dangerous drugs. On the other hand, the decline in hard drug usage supports the theory that the nation’s youth have replaced more harmful drugs, such as crack, with marijuana.

Researchers note how this new marijuana epidemic is similar in nature to previous drug epidemics. The report explains how a drug’s popularity follows a bell-curve trajectory: starting out slow, growing exponentially, leveling off, and then dying down. Previous drug epidemics, including the widespread marijuana usage in the late 1960s and early 70s and the destructive crack epidemic of the late 1980s, reflect this cycle.

Drug epidemics demonstrate the diffusion of innovation in a social network. It starts with a small group of drug users and spreads like a virus through the network, infecting other nodes as it grows in popularity. These early adopters cause a cascade in the community where many others begin to use the drug as well. For this reason, drug epidemics seem to explode on the scene and seemingly come from nowhere, as was the case with the 1980s crack epidemic. The report also notes the importance of local differences in the spread of the epidemic. The life cycle of the drug scourge is wildly different in various communities and locations: sometimes severe and long-lasting, sometimes mild and short-lived, and sometimes not occurring at all. This fact underscores the significance of local differences, especially the cascade threshold and structure of the network in the spread of the drug epidemic.

The marijuana craze forty years ago illustrates the life cycle of an epidemic and shows how it was able to spread within certain communities. In the tumultuous Vietnam era, marijuana became the drug of choice for the so-called “hippie movement” and the rebellious anti-war set. Originating in a small group of drug-users, it spread to college campuses and towns across the country, popularized in part by musical groups who promoted its use. The drug became socially acceptable in many communities but was shunned in others. The epidemic leveled off as it reached an equilibrium among users and non-users. After the war ended, changes in social mores and the aging of the Baby Boomers, its primary users, led to a decline in the popularity of marijuana.

http://www.ncjrs.gov/txtfiles1/nij/187490.txt