A study has found that the structural difference in the brains of people who use drugs may be present before experimentation with substances, casting doubt on the contested gateway theory that soft drug experimentation leads to harder drug use.
Scientists studied the brains of nearly 10,000 adolescents under the age of 15 to understand if some people are born with a pre-existing vulnerability that makes it more likely they will take drugs early in their life, or if environmental influences lead to drug use.
Early experimentation with softer drugs, such as cannabis and alcohol, is often linked to heavy and damaging drug use later in life. This has been dubbed the gateway drug theory. The theory states that after a young person tries cannabis or alcohol at a young age they will be more likely to try harder, more harmful drugs such as cocaine and heroin as they grow older. This theory was said to be proven by the likelihood that those who do have a problematic relationship with drugs often try substances such as cannabis first. However, causation and correlation are not the same thing.
In a study published on the Jama Network, analysis of brain scans from 9804 children showed differences in brain structure and size of those who had experimented with drugs early in their life which were present before their first experiences with drugs.
The children involved in the study were recruited from the ages of 9 to 11 and assessed for 3 years using data supplied from the ongoing Adolescent Brain Cognitive Development Study. Brain images from MRIs, as well as personal information about the child’s environment, were analysed to look for certain brain measurements and factors which may influence the initiation of drug use.
“Self-reported alcohol, nicotine, cannabis, and other substance use initiation and baseline magnetic resonance imaging (MRI)–derived estimates of brain structure (ie, global and regional cortical volume, thickness, surface area, sulcal depth, and subcortical volume). Covariates included family (eg, familial relationships), pregnancy (eg, prenatal exposure to substances), child (eg, sex and pubertal status), and MRI (eg, scanner model) variables,” the study authors explained.
The results of the analysis showed that 35%, (3460 children) initiated drug use prior to their 15th birthday and that those who did so were more likely to have different brain structures than those who didn’t try drugs. These differences were noted before and after drug use, which suggests a predetermination for drug use, which doesn’t align with the gateway drug theory.
“Among 9804 children with non-missing baseline neuroimaging and covariate data, 3460 (35.3%) reported substance use initiation before age 15. Initiation of any substance or alcohol use was associated with thinner cortex in prefrontal regions … but thicker cortex in all other lobes, larger globus pallidus and hippocampal volumes, as well as greater global indices of brain structure … following Bonferroni or false discovery rate multiple testing correction. Cannabis use initiation was associated with lower right caudate volume. Post hoc examinations restricting to postbaseline initiation suggested that the majority of associations including thinner prefrontal cortex and greater whole brain volume, preceded initiation,” wrote the study authors.
Researchers concluded that pre-existing brain structure was an indicator of adolescent drug use, often leading to drug use and sometimes drug-related problems in later life. However, the authors stress that this pre-existing indicator does not mean that children with a different brain structure will take drugs, just that they are more likely to.
“In this cohort study of 9804 children, we identified neuroanatomical features associated with substance use initiation that were present before substance exposure. Convergent with evidence from genetically informed (eg, discordant twin or sibling)7,14,23 and other longitudinal research,7,10,18 our data increasingly place interpretations that substance-related variability solely arises from substance exposure on a procrustean bed,” the study said. “Ultimately, a greater understanding of the links between brain structure and substance involvement may uncover predispositional risk factors that provide insight into the early causes of SUDs and clinically informative mechanisms through which myriad adverse health outcomes associated with substance involvement emerge.”
