A Systematic Review of Gender Representation in Neuroimaging Research in Drug Abuse Populations

Introduction/Objectives: Gender and race disparities in research participation have long plagued fields of biomedical research. These disparities limit the generalizability of research findings and can further perpetuate health disparities for marginalized groups. One such area that is significantly limited by a lack of sample diversity is clinical substance abuse research. A growing body of evidence suggests gender differences in substance uptake, withdrawal, response to medication treatments, and neurocognitive effects. However, there is a marked lack of research further investigating these supposed differences, particularly for non-alcohol drugs of abuse. In the current study, we intended to assess the extent of this issue in neuroimaging studies by systematically reviewing neurocognitive-based drug abuse research. Further, we wished to identify any preliminary gender-based trends in this body of literature.

Methods: The database search was conducted on April 25, 2023, in MEDLINE (via PubMed), PsychInfo, and Embase. The search strings used were designed to be broad and were intended to identify original research studies using neuroimaging techniques to assess cognitive functioning in substance users. The resulting articles were screened in a masked, duplicate fashion, with disagreements being resolved through discussion. Data was later extracted from included articles in a similar fashion with discrepancies being resolved by a third researcher. All procedures were conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

Results: Out of the 22,403 studies yielded by our initial search, 154 studies met the inclusion criteria. We found a notable lack of female participants across the included studies, with women only representing 22.77% of participants. As such, gender proportions within individual studies were often skewed towards men, with only 24.0% of the included studies having a roughly equal or higher percentage (operationalized as a >40% female sample) of female participants. For some drug types, such as cocaine, these proportions were even lower with only 17.24% of studies meeting the >40% female participant threshold. Furthermore, nearly a quarter of the studies did not include any women in their samples. Likewise, few studies performed gender-based data analyses, with 11 of these reporting some type of significant gender difference. However, no major conclusions about neurological gender differences within the context of drug use could be made in the current study due to heterogeneity in study characteristics.

Conclusions: We identified a clear gender disparity in imaging-based drug use research participation. Significant efforts by researchers and research institutions must be made in order to expand this body of knowledge. Further, increased exploration into the underlying gender differences of addiction can be used to better inform clinical interventions, possibly leading to improved outcomes for women with substance use disorders.