Years ago, I sat in D.A.R.E. class as teachers warned of the harm of cannabis. Not only would it destroy your brain, but it would lead to harder and more dangerous drugs (side note: I find it funny that cannabis is listed as a Schedule I drug in part out of fear that it would lead to the use of Schedule 2 drugs, like cocaine and morphine). Is this true? Does cannabis itself alter the brain in such a way that makes users more likely to graduate to other drugs?

Well, no.

The political history

Cannabis is not a “gateway drug”. Even those who toiled to make it illegal admitted that it was not the gateway to heroin. The Federal Bureau of Narcotics chief, Harry Anslinger, made it his mission to prohibit cannabis (which he deliberately called “marijuana” to associate it with Mexican immigrants). Throughout the 1930s, he cajoled newspapers, Hollywood, and politicians in a grand effort to make cannabis illegal. His efforts culminated with the passing of the 1937 Tax Act, which essentially made cannabis illegal to possess. In these hearings before the Committee on Ways and Means (75th Congress, 1st Session: House Marijuana Hearings), Anslinger was was asked if cannabis users graduate to heroin or cocaine.

“No sir,” he responded. “I have not heard of a case of that kind. I think it is an entirely different class. The marijuana addict does not go in that direction.”

12 years later, as the Cold War was heating up, Anslinger changed his view. He likened cannabis to a falling domino stating that cannabis addicts graduate to heroin once the thrill of weed is gone. This resonated with people of the era who were familiar with the idea of Communism toppling one country after the other, like a domino.

The idea stuck and persisted through the Nancy Reagan, “Just Say No” era.

What does the science say?

The science in unclear, at best. On one hand, studies show that cannabis use precedes other drug use. But this by no means indicates that cannabis causes other drug use. Instead, it is commonly believed that the reason cannabis precedes other drug use is that it is more easily accessible. Under this reasoning, nicotine, tobacco, and alcohol would also be considered “gateway drugs”. It’s clear that accessibility plays a major role individual use patterns.

Of concern is the impact of cannabis (mainly THC-rich cannabis) on the developing brain. Adolescent exposure to THC impairs dopamine signaling in the brain in response to other rewards. This affects the strength of drug-associated reward, and hypothetically, lead to the use of harder drugs in order to achieve a strong high. Consistent with this idea, rats exposed to large amounts of THC (or just their parents!) are more likely to seek heroin in adulthood.

But this doesn’t mean people behave like this in the real world. For one, we’re given more choices for how to live our lives than rats in a cage. And just because there may be some shift in brain chemistry, it’s unlikely to sufficiently alter reward perception to the point that heroin is the only means of living a pleasurable life.

To date, there haven’t been any studies linking adolescent cannabis use to harder drug use that aren’t confounded by genetic, environmental, or socio-economic factors. So given our current level of scientific and political understanding, the simplest answer to the question, is cannabis a gateway drug? is NO. The main reasons being: 1) an historical perspective reveals that this stance was taken for political reasons, and not based on science; 2) conformational bias leads us to confirm our belief that cannabis is a gateway drug because “hard drug” is often preceded by cannabis, even though cannabis is merely the more easily accessible and economic choice.

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