Still Dazed and Confused: Demographic Drift and the Persistence of Sampling Bias in Cannabis Research

Cannabis use has shifted dramatically over the past two decades, with the fastest growth occurring among adults aged 65 and older. The clinical trial, neuroimaging, inflammation, and psychiatric outcome literatures on cannabis have not kept pace with this change. This narrative review argues that cannabis research suffers from both dimensions of a Dual Diversity problem: a population diversity deficit, in which study samples remain skewed toward young, healthy, often university-recruited participants relative to actual users, and heterogeneity suppression, in which a demographically varied user population is analyzed as a single, uniform exposure group. This mismatch is traced across five domains. A documented clinical trial diversity gap has been quantified but not yet addressed. Patients using cannabis for neurological disease and chronic pain self-medicate ahead of an evidence base built for a different population. Neuroimaging studies of older-adult cohorts report divergent structural findings that may reflect participant and exposure heterogeneity, among other possible explanations. Inflammatory and endocannabinoid physiology change with age in ways young-skewed samples rarely capture. Psychosis-risk research remains concentrated in adolescence despite implications for older, more recent initiates. The review closes with concrete recommendations, including population-benchmarked reporting, age-stratified enrollment modeled on ICH E7, heterogeneity-preserving analysis, and a minimum exposure descriptor set.