The potential of methamphetamine, and high-potency crystal methamphetamine in particular, to precipitate psychotic symptoms and psychotic illness is the subject of much speculation internationally. Established psychotic illness is disabling for individuals and costly to society. The aim of this study was to investigate whether use of crystal methamphetamine was associated with greater prevalence of self-reported psychotic illness, compared to use of other forms of methamphetamine.

The sample comprised participants interviewed as part of an annual cross-sectional survey of Australian people who inject drugs. Comparisons were made between groups according to the nature of their methamphetamine use: crystal methamphetamine or other forms of methamphetamine. Self-reported diagnoses of psychotic illness and other mental health problems were compared between groups. Predictors of self-reported psychotic illness were examined using multivariable logistic regression analyses.

Self-reported psychotic illness was highly prevalent among users of crystal methamphetamine (12.0%), and significantly more so than among users of other forms of methamphetamine (3.9%) (OR=3.36; CI: 1.03-10.97). Significant predictors of self-reported psychosis in the cohort were: use of crystal methamphetamine; dependent use; lack of education beyond high school; and younger age.

Highly increased prevalence of self-reported psychotic illness is associated with use of high-potency crystal methamphetamine in people who inject drugs, particularly where there is dependent use. There is an urgent need to develop effective interventions for dependent crystal methamphetamine use; and a need to monitor for symptoms of psychotic illness in drug-using populations.