The classic myth of marijuana as a ‘gateway drug’ for other substance use is controversial. Because marijuana use is just one of hundreds or potential risk factors for other substance use, its exact contribution is difficult to say for certain. While undeniable population trends exist, deciphering the cause-and-effect relationships between marijuana and other risk factors for co-substance abuse is a considerable challenge.
It is true marijuana use has an alarmingly high rate of co-occurrence with other types of substance use. The more you smoke, the stronger association with other substance use becomes. One study found that daily marijuana use was associated with a significant increase in the expected odds of opiate, cocaine, stimulant, hallucinogen, inhalant, and tobacco use (Tzilos, J Addict Dis, 2014). Daily marijuana users have been singled out as being particularly vulnerable to the additive negative consequences associated with polysubstance abuse.
Even so, the association between marijuana use and other substance use doesn’t point to a direct cause and effect. One possibility is that the risk factors that predispose you to using marijuana also predispose you to using other substances. Alternatively, marijuana use may be an independent risk factor for using other drugs (the “gateway drug” hypothesis). Time and more research will tell how much marijuana use directly contributes to likelihood of using other drugs.