According to Stages and Pathways of Drug Involvement: Examining the Gateway Hypothesis, the gateway theory of substance abuse is the idea that use of one particular substance will lead individuals to subsequently be at a greater risk to abuse other substances. The idea was extremely popular in the 1970s and 1980s when the term gateway theory was coined in order to bring attention to the so-called War on Drugs and to single out specific drugs like marijuana as dangerous substances. Recently, with the legalization of cannabis products in a number of states for medicinal uses and even for recreational purposes, a number of politicians have been voicing their disapproval of the new legislation referring back to the gateway hypothesis.
The supporters of the gateway hypothesis for drug abuse point to basically two overarching conditions that could result in certain types of substances making individuals more vulnerable to abusing other substances. The concepts are often divided but are not mutually exclusive.
A gateway drug alters neuropathways in the brain. Animal models of addiction have indicated that animals that begin to use certain types of substances at an early age are at an increased probability to develop addictive behaviors to other substances. When these animals are studied, postmortem findings indicate that certain areas of their brain (e.g., the so-called reward system) are altered compared to normal animals. Thus, it is concluded that early use of certain drugs leads animals to become more vulnerable to develop abuse issues with other drugs. These experimental models appear similar to observational data in humans that suggest that individuals who use certain drugs at an early age are more likely to use other drugs later.
An interaction of genes and environment is involved. Twin studies in humans suggest that there is a significant genetic component to drug abuse, and this is reflected in individuals who abuse more than one substance. Thus, certain inherent factors may contribute to the alteration of neuropathways in individuals and account for the gateway hypothesis. Researchers who study drug abuse have observed that a number of environmental and even personal factors are associated with poly-substance abuse. Thus, the gateway hypothesis assumes that the interaction of inherent factors with experience may produce situations that foster the gateway theory.
These explanations for the feasibility of a gateway hypothesis are in contrast to what is known as the shared factors or common liability model that seeks to explain the relationship between different types of co-occurring or comorbid mental health disorders. This model views the relationship as a nonspecific liability that results in individuals who have one type of mental health disorder being at greater risk for additional mental health disorders. The gateway hypothesis proposes a specific relationship between the use of one drug and later use of other drugs, whereas the common liability model suggests that individuals who develop an abuse issue to any drug are at a greater risk to develop any number of mental health disorders, including an increased risk for further abuse of other drugs.
Although any drug of abuse could be a potential gateway drug if the gateway hypothesis is valid, only a few drugs are commonly targeted as potential gateway drugs.
Tobacco shares a number of close associations with the use and abuse of other drugs. According to the National Institute on Drug Abuse (NIDA), tobacco use is the leading cause of death and disability in the United States. A number of studies have indicated that individuals who begin using tobacco products earlier in life will often develop other issues with substance use and abuse, including to substances like alcohol, marijuana, cocaine, heroin, etc.
A study published in the Journal of School Health in 1997 elucidated the factors that could conceivably explain nicotine’s status as a potential gateway drug. These factors included learning theory (being reinforced for the use of nicotine generalizes other drugs), pharmacological issues (biological similarities in changes associated with nicotine use and other drugs), social factors, and beliefs about health in general. The researchers suggest that these factors explain nicotine’s potential as a gateway drug for a number of other drugs of abuse, including alcohol, cocaine, heroin, etc.
A study published in the journal Science Translational Medicine in 2011 found that rodents given nicotine-laced water early in their development demonstrated enhanced responses to cocaine later.
The Centers for Disease Control and Prevention (CDC) presents data that indicates there is an association between tobacco use and illicit drug use.
Like nicotine, alcohol is also often referred to as a gateway drug. A number of studies suggest this possibility.
According to data presented by SAMHSA in 2015, 20.8 million people over the age of 12 had a substance use disorder and 15.7 million of these people had an alcohol use disorder.
The large and ongoing Monitoring the Future Project surveys 50,000 students in 8th, 10th, and 12th grade each year to compile their data. Findings suggest that:
The substance that is most often accused of being a gateway drug is marijuana. A large number of research studies suggest that individuals who abuse other substances at least tried marijuana initially.
A number of animal studies indicate that exposing young rodents to THC early increases their potential to develop addictions to other drugs. Early exposure to THC results in a number of changes in the neuropathways of rodents that may make them more susceptible to addiction.
A large longitudinal study covering 25 years reported in the journal Addiction indicated that early marijuana use was strongly associated with later and more frequent drug use and abuse.
A 2015 study in the International Journal of Drug Policy used data from the National Epidemiological Survey on Alcohol and Related Conditions and looked over 6,600 individuals who reported using cannabis prior to the use of any other drug. Results indicated that there was a 44.7 percent chance that this group would use other drugs, a significantly higher chance than in the general population.
Despite the large body of evidence that indicates that animals and even humans who use certain drugs, such as alcohol, tobacco, or marijuana, also abuse other drugs later, the gateway theory is hotly contested among researchers and clinicians. According to a number of sources, including The Everything Guide to the Human Brain, many of the issues with the gateway theory are related to a number of methodological limitations of the research that supports it.
There are problems with animal models of behavior: First, animal models of behavior do not often generalize with humans. Animals in cages that self-administer substances represent a far cry from the conditions that most animals live in, and these models certainly do not generalize well to people. For instance, animals living in enriched environments as opposed to the conditions typically imposed on them in addiction models of behavior do not tend to self-administer drugs. While animal models can help to develop a basis for hypothesizing as to how a specific behavior in humans might occur, they do not fully explain the complex behaviors that people engage in.
Correlation does not infer causation: One of the most frequently forgotten rules of research is that studies that look at associations (correlations) cannot be used as evidence of a causal relationship between the variables in them. All of the studies that are used to demonstrate the relationship between substance use/abuse in human beings are what are termed correlational studies. The studies look at associations, but they do not look at the causes and effects. Researchers can hypothesize regarding the relationships between the variables in the studies; however, these relationships do not imply that using marijuana early actually causes someone to use cocaine later.
The relationships between co-occurring disorders are extremely complex: The relationships that occur between comorbid or co-occurring mental health disorders are extremely complex and difficult to tease out. For instance, it may well be that the use of any potentially forbidden substance early in life represents more general tendencies toward antisocial behavior that result in the increased potential for use of other substances, or such a situation may be the result of simple associative learning. For example, individuals who use illicit drugs develop relationships with peers who are more likely to use these substances. Simply being in an environment where individuals are abusing illicit drugs will increase the probability that one will try and repeatedly use these drugs.
There are issues with biological or medical models of behavior: Even though animal models and neuroimaging studies in people suggest that the brain pathways of individuals who use specific drugs become significantly altered, this does not mean that these individuals are without choices. Part of the issue with medical models of behavior is that these models tend to promote the idea that individuals who have chronically abused drugs have lost the ability to choose whether or not they can use drugs. If that were true, then no substance use disorder treatment program would help these individuals because there are no medical treatments that can alter brain pathways such that they return to their state prior to drug abuse or to a state where these changes are identified as being fully resistant to future abuse of drugs. Cognitive Behavioral Therapy can help to reshape the brain to make better choices.
The common liability model better explains the relationships: The gateway theory attempts to designate one drug as being the “gateway” to developing other issues with drug abuse; however, there is sufficient evidence to suggest that using nearly any drug early on is associated with a higher potential to abuse other drugs later. How many gateway drugs are there? There is research that abusing prescription medications early is associated with higher rates of alcohol or marijuana use later; hence, essentially any substance could be a gateway drug. If any number of drugs could serve as gateway drugs, then these relationships better reflect the common liability model as opposed to the gateway theory.
There is evidence that using some substances early in development does result in a greater probability that an individual will abuse other substances; however, the reason for this is not well understood. This condition may represent some combination of inherent factors (e.g., genetic) and the interaction of environmental factors (e.g., peers, learning, stress, etc.).
The relationship between early alcohol use and later use of other drugs has the strongest evidence to suggest that it may be a gateway drug; however, the gateway theory suffers from a number of potential methodological flaws. At the current time, it is unable to specify a causal relationship between early use of any drug and the potential to use or abuse other drugs later. Instead, these relationships may be more consistent with the common liability model.