Analysis: Marijuana Use Data Fails to Support “Gateway Hypothesis”

Boise, Idaho: Claims that the initiation of marijuana use is independently linked to the later use of other controlled substances are not supported by longitudinal data, according to a study published in the Journal of Experimental Criminology.

A pair of researchers affiliated with Boise State University in Idaho analyzed the relationship between self-reported marijuana use in late-adolescence and the use of other illicit substances later in life in a nationally representative sample. 

Authors reported: “[P]olitical discourse advocating marijuana prohibition commonly hinges on the assumption that marijuana causes hard drug use. The MGH [marijuana gateway hypothesis] is by far the most common justification for prohibiting the use of cannabis. However, the current study provides further evidence that common liability arguments are more in line with substance use patterns observed in the USA.”

They concluded: “In sum, the findings from the current study … provide further support of previous research questioning the causal claims of the MGH. While there is strong support for correlation and sequencing in marijuana and hard drug use, correlation and sequencing alone cannot provide sufficient evidence for causality. Factors other than marijuana use such as genetic predisposition, peer associations, or access to the illicit drug market could be the primary causes of hard drug use instead of marijuana use itself. As such, any public policy that prohibits the use of marijuana in an attempt to curb hard drug use is unlikely to succeed.”

Full text of the study, “Is marijuana really a gateway drug? A nationally representative test of the marijuana gateway hypothesis using a propensity score matching design,” appears in the Journal of Experimental Criminology. Additional information is available from the NORML fact sheet, “Marijuana and the ‘Gateway Theory’.”