Gateway Theory: Does Cannabis Use Lead to Harder Drugs?

In the early 1980s the concept of cannabis being a “gateway” to the use of “harder” drugs was introduced as a justification for prohibition of cannabis and prosecution of users. Unfortunately, this Gateway Theory had not been scientifically investigated at the time it was introduced, and despite subsequent science that has demonstrated this theory to be incorrect, lawmakers and politicians continue to refer to it when justifying their positions. This article will summarize the actual data that has been accumulated over the ensuing 40 plus years since this theory made its debut.

What is the Gateway Theory?

The Gateway Theory suggests that cannabis use leads to the use of harder drugs, but this assumption fails to account for the broader factors that influence substance use. While many users of harder drugs have previously used cannabis, correlation does not imply causation. A study by Degenhardt et al. (2010), which analyzed data from 17 countries, found that although cannabis use often precedes the use of harder drugs, this does not establish a causal relationship.

Instead, factors like availability, social environment, and individual personality traits better explain the progression to other substances than cannabis itself. Similarly, Macleod et al. (2004) found that when controlling for environmental and genetic factors, the association between cannabis use and later drug use disappears, suggesting that external influences, rather than cannabis use, are responsible for the observed progression.

The National Institute on Drug Abuse (NIDA) further supports this, stating that the majority of cannabis users do not transition to harder drugs. If cannabis were a gateway, we would expect consistent, direct links between cannabis use and the use of other substances, but this is not the case.

Common Liability Model

A more scientifically supported theory is the Common Liability Model, which suggests that genetic, environmental, and social factors predispose individuals to drug use, rather than cannabis acting as a gateway. Vanyukov et al. (2012) found that genetic and social factors are more influential in predisposing individuals to drug use than the pharmacological effects of cannabis itself. Twin studies have further shown that shared genetic and environmental factors, rather than cannabis use, are more predictive of later substance use.

For instance, if cannabis were a true gateway drug, twin studies would show that the cannabis-using twin would be significantly more likely to progress to harder drugs than their non-using sibling. However, research shows only minor differences. Additionally, early childhood adversity, such as trauma and abuse, is a stronger predictor of future substance use than cannabis use, highlighting the significance of underlying vulnerabilities in determining drug use outcomes.

Prohibition vs. Decriminalization

Furthermore, the role of prohibition in the supposed gateway effect cannot be overlooked. Golub & Johnson (2001) demonstrated that the gateway effect is largely a consequence of prohibition, where cannabis users must interact with illegal markets that also sell harder drugs. If cannabis were solely responsible for the progression to more dangerous substances, we would expect to see different trends in countries or regions with regulated cannabis markets.

In contrast, countries with decriminalization policies, such as Portugal, have not seen an increase in harder drug use following cannabis decriminalization. In fact, Portugal experienced a decline in problematic drug use, overdose deaths, and HIV transmission after decriminalization. The Netherlands, with its long-standing cannabis decriminalization policy, has lower rates of hard drug use compared to countries with stricter cannabis laws, further challenging the gateway theory.

These examples underscore that the criminalization of cannabis, rather than cannabis use itself, creates a pathway for exposure to illicit substances.

Longitudinal Studies

Longitudinal studies following cannabis users also fail to support the gateway hypothesis. A 20-year study by Fergusson et al. (2006) found that while cannabis use is associated with other drug use, this relationship significantly weakens when controlling for socio-environmental factors.

Similarly, Lynskey et al. (2003) examined twins where one used cannabis and the other did not, finding that the differences in the likelihood of using harder drugs were minimal, suggesting that other factors are more significant than cannabis use itself.

The National Academy of Sciences (2017) concluded that there is no substantial evidence to support the claim that cannabis use leads to the use of harder substances, instead highlighting the role of social and economic factors in determining drug use trajectories.

Legalization and Decriminalization

Lastly, evidence from countries and states that have legalized or decriminalized cannabis provides further support for the argument that cannabis is not a gateway drug. A study in Colorado (Anderson et al., 2019) found that cannabis legalization did not result in an increase in hard drug use.

Additionally, Pardini et al. (2015) found that mental health conditions and socioeconomic factors, rather than prior cannabis use, were the biggest predictors of drug abuse. In Washington state, youth cannabis use rates remained stable after legalization, contradicting concerns that legal access would lead to increased substance use.

Conclusion

In conclusion, the Gateway Theory is outdated and not supported by modern scientific research. The Common Liability Model provides a more accurate explanation for substance use patterns, demonstrating that genetic, environmental, and social factors play a greater role than cannabis use itself.

Moreover, prohibition-based policies may exacerbate drug-related harms by exposing cannabis users to illegal markets, while countries and states with regulated cannabis markets have not seen a rise in hard drug use.

Evidence suggests that cannabis legalization or decriminalization does not lead to increased substance use and may even reduce harm by limiting exposure to illicit substances.It is time to move beyond outdated theories and focus on evidence-based policies that prioritize public health and social justice.

References

1. Degenhardt, L., et al. (2010). The association between cannabis use and the use of other illicit drugs: A systematic review. The Lancet Psychiatry.
2. Macleod, J., et al. (2004). Psychological and social sequelae of cannabis and other illicit drug use by young people: A systematic review of longitudinal studies. The Lancet.
3. Vanyukov, M.M., et al. (2012). Common liability to addiction and “gateway hypothesis”: Theoretical, empirical, and evolutionary perspective. Drug and Alcohol Dependence.
4. Kendler, K.S., et al. (2012). Genetic and environmental influences on cannabis use initiation and progression to problems. Addiction.
5. Golub, A., & Johnson, B.D. (2001). The misuse of the “gateway theory” in U.S. policy on drug abuse control: A secondary analysis of the National Household Survey on Drug Abuse. American Journal of Public Health.
6. Hughes, C.E., & Stevens, A. (2010). What can we learn from the Portuguese decriminalization of illicit drugs? British Journal of Criminology.
7. Fergusson, D.M., et al. (2006). Cannabis use and other illicit drug use: Testing the cannabis gateway hypothesis. Addiction.
8. Lynskey, M.T., et al. (2003). Escalation of drug use in early-onset cannabis users vs co-twin controls. JAMA Psychiatry.
9. Anderson, D.M., et al. (2019). High on life? Medical marijuana laws and suicide. Journal of Health Economic.
10. Pardini, D.A., et al. (2015). Early predictors of age-related patterns of marijuana use among men. Drug and Alcohol Dependence.

Darynaisha Crawford has a BS in Biology & BA in Chemistry and is currently pursuing her Master’s of Science in Biomedical Technology with a concentration in Medical Cannabis Therapeutics. Her career goal is to receive her MD/PhD in Neuroscience to become a neurosurgeon and use medical cannabis to combat brain tumors. Darynaisha is also in the process of starting her own medical cannabis business.