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Philippe Lucas Philippe Lucas

Can We Unlock Marijuana’s Potential as an “Exit Drug”?


With the myth long since debunked that cannabis is the "gateway" to addiction ruin, increasing evidence points to its value as a substitute for far more dangerous substances, such as alcohol.

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Marijuana substitution effect

Weed’s substitution effect could redefine consumer choices. Photo via Shutterstock.

Cannabis is neither completely harmless nor a cure-all, but with polls showing that Americans and the citizens of Canada (where I live) overwhelmingly support marijuana policy reform, it’s fair to assume that most people no longer believe that legalization will lead to the end of the world. Yet some who support reform have concerns that adding yet another legal drug to the list—alcohol, tobacco and pharmaceuticals—that already causes many social harms and costs may result in an increase in even more problems.

For now the question of whether legalization causes an increase in the use of marijuana remains unanswered. Because the only jurisdictions in the world that have legalized adult cannabis use—Uruguay, Colorado and Washington—did so less than a year ago, there is no specific data, and the research on whether decriminalization causes increased use is contradictory.

But what if the legalization of marijuana results in a reduction in the use of alcohol and other substances? What if rather than being a “gateway” drug—the claim long marshaled by drug prohibitionists—cannabis actually proves to be a safer substitute for problematic use of other substances? And therefore a potential “exit” drug from such use?

A growing body of research on a theory called “cannabis substitution effect” suggests just that. (Full disclosure: In addition to being an advocate for the reform of drug policy, I am a researcher employed at a Canadian company that cultivates, tests and distributes medical marijuana.)

1. The Gateway Hypothesis

The premise of the “gateway,” or “stepping stone,” hypothesis is that the use of one substance may lead to the use of another. With regard to illicit substance use, this theory suggests that the use of cannabis may facilitate the use of potentially more harmful, addictive drugs such as opiates, cocaine or amphetamines.

The evidence for the gateway theory is based on research published in 2006 indicating that most people who use hard drugs report a prior use of marijuana. The authors write:

“The ‘gateway theory’ is comprised of two interrelated observations. The first is that marijuana use is associated with later, non-marijuana, illicit drug use, and the second is that there is a temporal ordering of substance experimentation in which lower order substances, which are more commonly used, precede the use of higher order substances. Thus, typically one licit substance such as alcohol or cigarettes is used first in a sequence. Marijuana is usually the first illicit substance used before progressing on to using other illicit substances.”

While most research has focused on the social or economic factors that can lead users of cannabis to experiment with other substances, some research suggests that this progression may partly be due to biological changes in individuals exposed to marijuana.

Whatever the factors, the “gateway” hypothesis is one of the primary reasons cited by lawmakers and police for keeping cannabis use illegal, despite its low potential for individual harm or misuse and its minimal impact on public health and other social costs.

However, research has thoroughly debunked the “gateway” hypothesis. Canada’s Senate Special Committee on Illegal Drugs’ 2002 report on marijuana reviewed all of the available evidence and concluded:

“It is not cannabis itself that leads to other drug use but the combination of the following factors: personal and family history that predispose to early entry on a trajectory of use of psychoactive substances starting with alcohol; early introduction to cannabis, earlier than the average for experimenters, and more rapid progress toward a trajectory of regular use; frequenting of a marginal or deviant environment; and availability of various substances from the same dealers.”

Thus, while it may be true that many hard drug users have also used cannabis, the reasons range from social factors such as poverty to the illegal status of the substance, which results in black market control over its distribution.  As the  2002 Canadian report discovered, drug use trends in Canada simply do not support the “gateway” theory, given that more than 30% of people reported having used cannabis, but fewer than 4% have used cocaine and fewer than 1% heroin.

2. The Substitution Effect

By contrast, “substitution effect” is an economic theory suggesting that variations in the availability of one product may affect the demand and use of another. In this context, changes in either the medical or the recreational use of cannabis with regard to the use of other substances can be the result of the following factors: economic shifts affecting end-user costs; changes in policy that affect availability; legal risk and its repercussions; or psychoactive pharmacological substitution.

Prescription therapies for the treatment of drug misuse can themselves be viewed as “alternative commodities” that are used as a substitute for an illicit drug or as a means to reduce the illicit drug’s potency. The best example of deliberate drug substitution may be the common prescription use of methadone or Suboxone as a substitute for opiates, or the use of e-cigarettes or nicotine patches for tobacco smoking.

However, not all such substitution is the result of a deliberate decision made on an individual basis, and “substitution effect” can also be the unintended result of public policy shifts or other social changes, such as the cost, legal status or availability of a substance.  For example, in 13 US states that decriminalized recreational use of cannabis in the 1970s, a 1993 study found that users shifted from using hard drugs to marijuana after its legal risks were decreased. (The data was based on emergency room visits in decriminalized cities, which showed increases in marijuana mentions but significant reductions in the mention of hard drugs, compared with visits in nondecriminalized cities.)

Findings from Australia’s 2001 “National Drug Strategy Household Survey” specifically identify a cannabis substitution effect, indicating the 56.6% of people who used heroin substituted marijuana when their substance of choice was unavailable. The survey also found that 31.8% of people who used opiate (and other) painkillers for nonmedical purposes reported using marijuana when the analgesics were not available.

Additionally, a 2011 survey of 404 medical marijuana patients in Canada that colleagues and I conducted found that over 75% of respondents reported that they substituted marijuana for another substance, with over 67% using cannabis as a substitute for prescription drugs, 41% as a substitute for alcohol and 36% as a substitute for illicit substances.

This and other evidence that cannabis can be a substitute for pharmaceutical opiates, alcohol and other drugs—and thereby reduce alcohol-related automobile accidents, violence and property crime, as well as disease transmission associated with injection drug use—could help inform an evidence-based, public health-centered drug policy. Given the potential to decrease personal suffering and the social costs associated with addiction, further research on the “cannabis substitution effect” is justified on both economic and ethical grounds.

Maximizing the public health benefits of cannabis as an “exit drug” may require the legalization of marijuana, as in Colorado and Washington State. The question is: Do we have the courage to abandon longstanding drug policies based on fear, prejudice and misinformation and instead initiate strategies informed by science, reason and compassion?

Philippe Lucas is the vice president of patient research and services at Tilray, a federally authorized medical cannabis production company located in British Columbia. He is a graduate researcher with the Centre for Addictions Research of British Columbia, and a founding Board member of the Canadian Drug Policy Coalition and the Multidisciplinary Association of Psychedelic Studies (MAPS) Canada. In 2012 he was awarded the Queen Elizabeth II Diamond Jubilee Medal for his work on medical cannabis. His website is here.