Mythbusting the Gateway Theory: Correlation vs. Causation

We can trace the “gateway theory” to the 1930s, and even then public health experts knew it was based on anti-drug hysteria rather than science.1 It’s a destructive myth, and it hasn’t aged well.

The gateway theory is the notion that cannabis use leads to use of more dangerous drugs. But for nearly 100 years, the public health community has confidently refuted these hyperbolic claims. Even in the darkest days of the drug war, there have always been physicians who spoke truth to propaganda: evidence does not support a causal link between cannabis and the later use of hard drugs.

People who use hard drugs often have tried cannabis earlier in their lives because of its wide availability and relative safety. They are even more likely to have tried alcohol and tobacco. For obvious reasons, people generally try less dangerous drugs before trying more dangerous drugs, which may be harder to obtain. But a simple observation reflects the reality: The vast majority of people who use cannabis, tobacco, and alcohol never go on to use more dangerous drugs.

Since the “reefer madness” of the 1930s, prohibitionists have made unfounded inferences from the unsurprising fact that people who use opioids have often consumed cannabis first. They’re also more likely to have tried alcohol, tobacco, caffeine, and cupcakes first. The fallacious gateway theory nonetheless influenced the U.S. Federal Government when it banned cannabis in 1937.

Over eighty years later, the gateway theory remains unsupported by scientific research. The Institute of Medicine, the health division of the National Academy of Sciences, has concluded that cannabis “does not appear to be a gateway drug to the extent that it is the cause or even that it is the most significant predictor of serious drug abuse.”2

Simply put, cannabis does not cause people to use hard drugs. It’s like your high school science teacher often said: “Correlation does not equal causation.”

Studies show that other factors—including genetic predisposition, environment, and poverty—are highly correlated with and can predict substance use disorders. The misuse of so-called soft drugs are, at most, indicators of some people’s predisposition to misusing other drugs. This more enlightened view of cause and effect in drug use is known as “common liability theory.”

The gateway theory is a misleading explanation of the complicated set of factors that actually lead to substance misuse. Its reductive interpretation distracts from an important public health discussion, and this malignant misunderstanding has resulted in the many harms of cannabis prohibition.

Especially given the severity of the United States opioid crisis, we need research and preventive education that focuses on the demonstrable links to the use of hard drugs, including genetics, poverty, and social environment.3

According to the Oxford Dictionary, a theory is a “supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained.”4 By this definition, we should more properly speak of the “gateway myth.”

One way cannabis can causally lead to the use of hard drugs is through its prohibition.

Wherever the cannabis trade is illegal, it is sold to anyone—including minors. In a legalized environment, cannabis sales are separated from those of hard drugs, and minors are excluded from purchases.

The bottom line: Legalization makes communities safer and actually separates the sales of cannabis from other, far more harmful drugs. This is just one of many reasons why America needs legalization now.

Thanks to New Jersey United for Marijuana Reform ( for their collaboration on this article.

1Doctors for Cannabis Regulation, “The Prescience of William C. Woodward.”

2Joy, Janet E., et al. Marijuana and Medicine: Assessing the Science Base. Washington, DC: National Academy Press, 1999, pp. 100-101.

3Quenqua, Douglas. “A Comeback for the Gateway Drug Theory?” The New York Times, December 7, 2017. See also: Valdez, Avelardo et. al. “Aggressive Crime, Alcohol and Drug Use, and Concentrated Poverty in 24 U.S. Urban Areas.” Am J Drug Alcohol Abuse. 2007; 33(4): 595–603.

4“Theory.” Oxford Living Dictionaries