With marijuana becoming legal in several states, including Colorado, there have been new echoes of the old argument that marijuana is a gateway drug, meaning people who use marijuana are more likely to go on to use other drugs such as cocaine or heroin. While it seems possible that marijuana might entice people to try harder drugs, the relationship between marijuana use and using other drugs is complicated.
First, as with any drug, the earlier you use marijuana, the more likely you are to have substance use problems later on. Early age of first use is a strong predictor of addiction. Marijuana is relatively accessible so it is commonly used by people at a young age. In that way, using marijuana as an adolescent may make you more vulnerable to addiction, including addiction to harder drugs. There also seems to be some evidence that marijuana makes you more sensitive to the effects of other drugs, a phenomenon called cross-sensitization. We also shouldn’t ignore the fact that people do develop addictions to marijuana itself, which can disrupt their lives even if they never escalate to other drugs. In those ways, marijuana may be a gateway drug.
In other ways, the case isn’t so clear. For example, according to a recent poll, more than half of American adults have used marijuana at some point. About 78 million say they’ve tried it once, about 20 million use it about once a year, and about 35 million use it about once a month. In other words, of the roughly 133 million Americans who have used marijuana at some point, only about a quarter use it once a month or more. By comparison, in 2016 fewer than a million people reported using heroin in the past year. That means less than 0.7 percent of people who have used marijuana go on to use heroin. That’s hardly an airtight case for marijuana as a gateway drug.
A more plausible candidate for a gateway drug is alcohol. Almost two thirds of people say alcohol was the first psychoactive substance they used, compared to only 18 percent who say marijuana was their first substance. Alcohol has the same cross-sensitization effect as marijuana,is far easier to get, and is on average used at a much younger age. Alcohol is more addictive and many people addicted to other drugs are also addicted to alcohol. People who try to quit drugs without also quitting drinking, often find alcohol is a powerful trigger for drug use, causing cravings and also undermining their judgment and willpower.
Addiction is complex and is caused by the interaction of several different factors, including genes, childhood trauma, mental illness, and social connection. While many people who are addicted to harder drugs have also used marijuana, marijuana use alone without other risk factors is unlikely to lead to addiction.