This is a question that often comes up in debates about drug policy. The gateway theory holds that the use of “softer” drugs will lead to the use of “harder” drugs, such as cocaine, methamphetamines, and heroin. Marijuana is frequently identified as a gateway drug, and an oft-cited argument against ending marijuana prohibition is that its use leads to more serious drug use. Data on drug use and scientific research do not support this claim.
For more than four decades, the National Survey on Drug Use and Health (NSDUH) has collected annual data on drug use from roughly 70,000 people over the age of 12. These data are the most authoritative source of information on drug use trends available in the US. In 2015, 44 percent of people ages 12 and older—and more than half of those under the age of 60—reported having used marijuana at some point in their lifetime. However, only 8.3 percent said they used marijuana regularly, measured as use in the past 30 days. This suggests that while many people experiment with marijuana, few go on to make it a habit. In other words, “marijuana is for most people who try it not even a gateway to more marijuana use.”
If marijuana was a gateway drug, we would expect to see use rates for “harder” drugs roughly on par with marijuana use rates. But while 8.3 percent of people 12 and older said they used marijuana in the last 30 days in 2015, only .7 percent of this population said they had used cocaine in the last month and only .1 percent said they had used heroin. Scientific research on the effects of marijuana use also has found no evidence that using marijuana leads people to use other drugs.
This does not mean there is no connection between marijuana and other drugs. Prohibition requires marijuana users to rely on the black market, increasing the likelihood that they will come into contact with more harmful drugs and people who use and sell those drugs. And many, if not most, people who have tried cocaine or heroin have probably also used marijuana, as marijuana is the most commonly used illicit drug. But the relationship between marijuana and harder drugs has less to do with the physiological effects of the drugs themselves and much more to do with particular environmental, psychological, and genetic factors that are unique to the individual user.
For instance, data from the NSDUH show that several groups—males, people aged 18-25, non-college graduates, sexual minority adults (defined as those who identify as lesbian, gay, or bisexual), people living with mental illness, and adolescents with behavioral problems or unstable family environments —are at greater risk of developing a substance use disorder than other groups, regardless of their marijuana use. It is also important not to ignore the role of tobacco and alcohol, both of which are associated with an increased likelihood of illicit drug use among adolescents. But the factors that lead a person to hard drug use or dependence are complex and have more to do with individual circumstances than with prior use of other substances. Unfortunately most current drug policies do not reflect this fact.