Cannabis is neither completely harmless, nor it is a cure-all, but with a number of jurisdictions now looking to regulate adult access to cannabis rather than criminalize users, it’s fair to assume that most people no longer believe that decriminalization or legalization would lead to the end of the world.  However, some who oppose the current war on drugs still have concerns that legalization would result in an increase in use, therefore adding yet another legal drug for society to struggle with, along with alcohol, tobacco and pharmaceuticals. 

But what if legalization adult access to cannabis also resulted in a reduction in the use and abuse of alcohol and other drugs?  What if rather than being a gateway drug – which is a long disproven theory - cannabis actually proved to be an exit drug to problematic substance use? 

A growing body of research on a theory called cannabis substitution effect suggests just that.

In a nutshell, substitution effect is an economic theory that suggests that variations in the availability of one product may affect the use of another.  Perhaps the best example of deliberate drug substitution is the common prescription use of methadone as a substitute to heroin, or e-cigarettes or the patch rather than tobacco smoking. 

However, at the population level, substitution effect can be also be the unintended result of public policy shifts or other social changes, such as changes in the cost, legal status or availability of a substance.  For example, in an examination of hospital drug episodes in 13 U.S. states that decriminalized the personal recreational use of cannabis in the 1970s, Model found that users shifted from using harder drugs to marijuana after its legal risks were decreased (Model, 1993).

Findings from Australia’s 2001 National Drug Strategy Household Survey specifically identify cannabis substitution effect, indicating 56.6% of heroin users substituted cannabis when their substance of choice was unavailable.  The survey also found that 31.8% of people who use pharmaceutical analgesics for nonmedical purposes reported using cannabis when painkillers weren’t available (Aharonovich et al., 2002).

More recently Bacchuber et al. (2014) found that U.S. states that enacted medial cannabis laws between 1999-2010 had a 25% lower opioid overdose mortality rate compared to states without such laws, and that this effect generally strengthened over time.

This is supported by the results of a national survey of 628 medical cannabis patients conducted in Canada in 2011/12 which found that over 87% of respondents reported they substitute cannabis for another substance, with 80% using cannabis as a substitute for prescription drugs, 52% as a substitute for alcohol, and 32% as a substitute for illicit substances (Lucas et al., in press, Drug & Alcohol Review).

This and other evidence that cannabis can be a substitute for pharmaceutical opiates, alcohol and other drugs - and thereby reduce alcohol-related automobile accidents, domestic violence, assaults, homicides, and property crime, as well as disease transmission associated with injection drug use - could 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 cannabis substitution effect appears to be justified on both economic and ethical grounds.

Ultimately, options to maximize the public health benefits of cannabis substitution effect and reduce the harms of drug prohibition could include optimizing and perhaps subsidizing access for patients who could benefit from its use, or even the legalization of adult cannabis use, as we have recently seen in Uruguay, and Colorado, Oregon, Alaska and Washington State.  However, that will require finally abandoning international drug policies based on fear, prejudice and misinformation, and instead focus on strategies informed by science, reason and compassion.


This article was submitted by Philippe Lucas: VP of Patient Research and Services for Tilray, Interim ED for CMCC, a PhD Scholar with the Centre for Addictions Research of BC, and a founding Board member of the Canadian Drug Policy Coalition. In 2012 he was awarded the Queen Elizabeth II Diamond Jubilee Medal for his work on medical cannabis.