Gateway drug effect

The gateway drug effect (alternatively, stepping-stone theory, escalation hypothesis, or progression hypothesis) are terms denoting the hypothesis that the use of a psychoactive substance is coupled to an increased probability of the use of further substances. Possible explanations for this connection include environmental influence, personality traits that favour seeking both soft and hard drugs, alterations in the brain due to earlier substance exposure, as well as similar attitudes of people who use different substances, and therefore experience a "common liability to addiction".

A 2018 literature review conducted by the National Institute of Justice, which analyzed 23 peer-reviewed research studies, concluded "that existing statistical research and analysis relevant to the "gateway" hypothesis has produced mixed results", and that "no causal link between cannabis use and the use of other illicit drugs can be claimed at this time." However, in 2020, the National Institute on Drug Abuse released a research report which supported allegations that marijuana is a "gateway" to more dangerous substance use, despite stating that "most people who use or have used cannabis do not go on to use other substances later in life". One of the peer-reviewed papers cited in the report claims that while "some studies have found that use of legal drugs or cannabis are not a requirement for the progression to other illicit drugs ... most studies have supported the "gateway sequence", although the authors of the study itself conceded that they were "not able to ascribe causality". A study in Spain has proven that lifetime cannabis use (as well as early age of onset) greatly increased the likelihood of later legal substance use, as well as illegal substances and polysubstance.