gateway drug
a substance whose use is thought to promote progression to using more harmful substances. For example, alcohol, tobacco, and cannabis are often considered to be gateways to heroin, cocaine, LSD, or PCP use. Introduced in the 1950s, the concept became the most popular framework for understanding drug use among adolescent populations, guiding prevention efforts and shaping governmental policy. However, research suggests that certain personality traits (see addictive personality), rather than the substances themselves, are more likely to be associated both with early drug use (e.g., of tobacco and alcohol) at a relatively young age and with the progression to drugs that have a higher abuse potential.