In 2012, Vanyukov et al published an article describing two separate views on the role that drugs play in initiating an addiction (Drug Alcohol Depend 2012;123:S3-S17). One is the “gateway theory” and the other is the “common liability to addiction concept.”

The gateway theory places the drug as the primary factor in initiating a substance use disorder (SUD). The belief is that exposure to a licit rewarding drug (e.g., tobacco or prescription opioid) begins a developmental process that progresses like a disease to a more serious stage, culminating in the use of an illicit drug (e.g., marijuana, heroin). Thus, in this theory, exposure to a drug initiates an SUD independent of the biology of the individual.

The gateway theory can be traced to 1975, with a paper by Kandel reporting on the frequency with which adolescent illicit drug users had previously used marijuana (Science 1975;190:912-914). The difficulty was the failure to demonstrate causality in the relationship. People who use cocaine or heroin have usually been exposed to marijuana or a licit drug; however, the majority of marijuana users partake of no other illicit drug, and many heroin users skip the “steps” of softer drug use (Drug Alcohol Depend 2012;123:S3-S17).

Gateway Theory Minimizes Biological Contribution to Addiction

Central to the gateway theory is that the locus of control is external, minimizing or eliminating the known biological contributions to the disease. The mechanism by which one drug purportedly seeds an SUD involving another has never been fully explained, yet the gateway theory remains a popular precept, likely because it is a simple explanation.

For example, U.S. Attorney General Loretta Lynch, speaking at the University of Kentucky, said marijuana was clearly not a gateway drug but that prescription opioids were the gateway to heroin. She said, “When we talk about heroin addiction, we usually … are talking about individuals that started out with a prescription drug problem, and then because they need more and more, they turn to heroin. In so many cases, it isn’t trafficking rings that introduce a person to opioids; it’s the household medicine cabinet. That’s the source.”

By this logic, drugs other than prescription opioids could also serve as a gateway to heroin use. According to the National Survey on Drug Use and Health 2011-2013, most people using heroin had used at least three other drugs before heroin. Yet the attorney general rightly disavows this theory. Again, addiction is not a stepped disease driving people from softer to harder drugs. Rather, the more likely theory is that people who develop SUDs have a shared vulnerability to other drugs of abuse based on biological factors, not on the sequence of exposures.

Genetics and Environment at Play

In contrast, common addiction liability can explain the clinical spectrum of SUDs not explained by the gateway theory. It does so by accounting for complex genetic and environmental factors that are activated in the disease of addiction. This concept takes, as its basis, the overlapping genetic and behavioral factors that are common among people with various SUDs and that do not depend on any particular drug exposure or sequence of exposures (Drug Alcohol Depend 2012;123:S3-S17).

State marijuana ballot initiatives are throwing the discussion of gateway exposure back into public consciousness, as policymakers ponder whether marijuana would help ameliorate or worsen the opioid abuse crisis. A New Zealand examination of the gateway question concluded that although marijuana use predates much harder drug use, many additional factors are also at play that include preexisting psychiatric disorders, differences or changes in brain chemistry, family histories of substance abuse (heredity) or other psychopathology, and prior association with illegal sources of drugs (Relihan T. Is Marijuana a Gateway Drug? The Recorder. October 30, 2016).

In accordance with the common addiction liability concept, people with an addiction to prescription opioids have a disease that is already expressed, and the person who subsequently seeks heroin is finding the most effective or affordable way to support the disease.

Muhuri et al emphasize this in showing that although prescription opioid abuse is a strong risk factor for heroin use and, indeed, most heroin users report having previously used prescription opioids nonmedically, heroin use among people who use prescription opioids for nonmedical reasons is rare, and the transition to heroin use appears to occur at a low rate (CBHSQ Data Review 2013). Understanding how the disease of addiction progresses is important to public health solutions to combat both prescription opioid and heroin addiction.

The Truth About the Gateway Theory of SUDs

Public policymakers seeking to solve the opioid crisis would be advised to acknowledge that the gateway theory of SUDs is unsubstantiated and potentially misleading. Disorders develop where there is genetic vulnerability and an environment that drives individuals to seek relief from the stresses in their lives. People vulnerable to developing SUDs have a common liability to substances of abuse that does not depend on a hierarchical sequence of exposures.

Solutions to the opioid crisis lie in understanding the biological, social and economic factors that drive demand to escape with illicit use of drugs. This means solutions will not be easy, quick or cheap. Anything less will likely have unintended consequences that could be more harmful than beneficial to society, people with SUDs and people with pain.

Originally published in Pain Medicine News.

Purchase my book, The Painful Truth: What Chronic Pain Is Really Like and Why It Matters to Each of Us (available on Amazon), or read a free excerpt here.

Find me here:

Twitter
Google+
Amazon and Facebook

Copyright 2016, Lynn Webster, MD