Locating Gambling Severity Within Polysubstance Involvement: The Specific Role of Methamphetamine in 9,421 Adults Entering Treatment

Gambling problems are common among people entering alcohol and other drug (AOD) treatment, yet they are easily missed and the substance-use patterns that mark them are poorly understood. Population research ties gambling to alcohol, a framing that may not hold in treatment populations where involvement is severe and mixed, and evidence points more consistently to stimulants. Using intake data from 9,421 adults entering Australian AOD treatment who reported past-year gambling, we asked whether gambling severity (PGSI) tracks broader non-alcohol polysubstance involvement, particular substances within it, or alcohol. Confirmatory factor analysis of ten WHO-ASSIST severity indicators identified a single non-alcohol polysubstance dimension, with alcohol loading only weakly and standing apart. Gambling severity was modelled on that dimension, substance-specific severity, and alcohol severity together, using ordinal logistic regression. The clearest and most specific association was with high-severity methamphetamine use (OR = 3.66), which held across gambling-severity thresholds in non-proportional odds models (OR = 3.04-3.43). The polysubstance dimension was independently but more modestly associated; high-severity alcohol was not once other involvement was accounted for. Associations for other substances were smaller, and several reflected shared polysubstance involvement rather than distinct effects. Gambling severity in this cohort was not primarily alcohol-centred, and was not associated uniformly by polysubstance involvement. It was most strongly associated with high-severity methamphetamine use within a broader non-alcohol context. Routine gambling screening remains warranted, and clients presenting with high-severity methamphetamine use and complex polysubstance profiles may warrant particular attention.