Why do we focus on the exception and not the rule? Examining the prevalence of mono- versus polysubstance use in the general population

Background and aimsSubstance use disorders (SUDs) are predominantly studied as drug class specific constructs (e.g. opioid versus alcohol use disorder). Polysubstance use (PSU), or the use of two or more substances from multiple drug classes, is only captured diagnostically by the co-occurrences of drug class-specific SUDs, and in many ways is relegated to a secondary position within the literature. However, this is not consistent with mounting empirical evidence regarding the high prevalence of PSU patterns compared with a mono-use pattern (i.e. all use contained within a single-drug class). The current study measured how many individuals in the general United States population could be characterized as having a mono-use versus PSU pattern. MethodsWe measured the prevalence of mono-use versus PSU in those who used substances in the past year, those with at least two symptoms of an SUD and in those who received treatment for alcohol/drug problems in the past year using data from the National Survey on Drug Use and Health (NSDUH) from years 2015-19. ResultsOf those who used substance(s) in the past year, 64% reported a mono-use pattern. Importantly, only 26% of those who had at least two symptoms of an SUD and 22% of those who received treatment for substance use reported a mono-use pattern. ConclusionsAlthough mono-use of drugs is common in the United States at the public health level, it is a much less common presentation than polysubstance use (PSU) among individuals of even mild substance use disorder severity. This means that common efforts to study substances in isolation do not focus upon the most common presentation of the phenomenon. We discuss the importance and implications of embracing a PSU framework in the study of substance misuse and substance use disorders.