Those who grew up when Drug Abuse Resistance Education (D.A.R.E.) pamphlets were common in the school counselor's office are probably familiar with the “gateway drug” theory, which suggests the use of one substance like cannabis or alcohol will send a person down the path to try “harder” drugs like cocaine or meth later in life.
The gateway drug theory and many other ideas about drug use have been put into question in recent years as more resources are dedicated to understanding substance use, which has been highly stigmatized for decades. After initially labeling cannabis as a gateway drug in 2010, President Joe Biden even later walked back his stance, saying in 2019: “I don’t think it is a gateway drug. There’s no evidence I’ve seen to suggest that.”
The roots of substance use disorder are complex and not fully understood, but one of the hallmarks of addiction is understood to be caused by repeated drug use that neurologically changes the brain. Because the use of one substance like alcohol or nicotine is associated with the use of other drugs like cannabis, many have drawn causal links between the use of various drugs in theories like the gateway drug hypothesis. However, this idea has been highly debated, and as the understanding of substance use has improved, scientists began to understand that people may have a “common liability” to substances in general and that drug use is influenced by a host of factors.
"Our behavior is determined basically by our brain and our experience, and our experience can affect our brain as well."
A new study published late December analyzed brain scans of adolescents before and after they first tried alcohol, nicotine or cannabis, shedding light on one factor that could be influencing whether people decide to start using drugs. Writing in JAMA Network Open, Dr. Alex Miller, the study’s lead author and an assistant professor of psychiatry at Indiana University School of Medicine, and his team found that adolescents who initiated substance use had differences in certain brain structures compared to kids who didn’t use drugs. Importantly, most differences existed before they started using alcohol, nicotine or cannabis.
“The study sort of helps us highlight which regions may be important to further explore, with respect to their association as pre-existing risk factors for substance use initiation,” Miller told Salon in a phone interview.
Structural brain differences have been previously found in people who use drugs and were assumed to be effects of drug use, said Dr. Jonathan Foulds, a professor of public health sciences at Penn State College of Medicine who was not involved in the study. This study shows certain differences were there among adolescents who used substances prior to use, meaning they could not have been caused by the substance use, he said.
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“Our behavior is determined basically by our brain and our experience, and our experience can affect our brain as well,” Foulds told Salon in a phone interview. This study "casts doubt on some of the prior gateway theories because it seems like many of the same brain differences that are a risk factor for nicotine use are also a risk factor for alcohol and cannabis use.”
The differences observed in the study were small but statistically significant within a large sample size close to 10,000 participants, Miller said. Specifically, those who initiated these substances before age 15 had larger overall brains and a thinner prefrontal cortex in certain regions compared to kids who didn’t initiate drug use. The prefrontal cortex is responsible for things like decision making and information processing, and some research has found that a thinner prefrontal cortex is associated with more impulsive behavior and risky decision making, which could be linked to kids initiating substance use, Miller said.
On the other hand, some of the measures observed in this study went in the opposite direction to what is observed in brain scans of people who have substance use disorder. For example, heavy drug use has been linked to smaller overall brain sizes, and heavy cannabis consumption has been linked to smaller hippocampal volumes. In this study, substance use was linked to larger overall brain sizes and larger hippocampal volumes.
Importantly, this doesn’t mean that children with these differences in anatomy will inevitably go on to try drugs, said Dr. Bertha Madras, a psychobiology professor at Harvard Medical School, who was not involved with the study either. There are dozens of risk factors that influence whether kids use drugs, including genetics, accessibility to substances, and the prenatal environment.
It may be that some other factor is influencing the anatomical differences and drug use, like a predisposition to risky behaviors or teens’ perception of how harmful substance use is, Madras.
“Integrating the whole picture would give us a much better view of what the risk factors for using drugs are and what the risk factors that are consequent to drug use are,” Madras told Salon in a phone interview.
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This analysis uses data from the Adolescent Brain Cognitive Development Study, which was designed to follow a large group of children over many years to help determine the neurological origins and consequences of substance use. Miller said he plans to use the data to try and tease out what is behind these brain differences and whether they are due to genetics or potential environmental risk factors.
In October, another study using the ABCD dataset found that certain brain activity in childhood could predict substance use initiation and that this was associated with children’s exposure to pollution.
“Understanding the complex interplay between the factors that contribute and that protect against drug use is crucial for informing effective prevention interventions and providing support for those who may be most vulnerable,” said Dr. Nora Volkow, the director of the National Institute on Drug Abuse in a press release.
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