“Is Marijuana Really a Gateway Drug? A Nationally Representative Test of the Marijuana Gateway Hypothesis Using a Propensity Score Matching Design”, 2021-04-06 (; similar):
Marijuana use has been proposed to serve as a “gateway” that increases the likelihood that users will engage in subsequent use of harder and more harmful substances, known as the marijuana gateway hypothesis (MGH). The current study refines and extends the literature on the MGH by testing the hypothesis using rigorous quasi-experimental, propensity score-matching methodology in a nationally representative sample.
Using 3 waves of data from the National Longitudinal Study of Adolescent to Adult Health (1994–8200222ya), 18 propensity score-matching tests of the marijuana gateway hypothesis were conducted. 6 of the 18 tests were statistically-significant; however, only 3 were substantively meaningful. These 3 tests found weak effects of frequent marijuana use on illicit drug use but they were also sensitive to hidden bias.
Results from this study indicate that marijuana use is not a reliable gateway cause of illicit drug use. As such, prohibition policies are unlikely to reduce illicit drug use.