To test (1) if there was a change in self-reported lifetime prevalence of meth/amphetamine use by birth cohort and (2) if the extent of under-reporting of meth/amphetamine use was associated with the proportion of the population who nominated meth/amphetamine as a drug problem.
Observational study using seven waves of repeated cross-sectional nationally representative household surveys between 2001 and 2019.
Participants were from three birth cohorts: 1951–60 (age 68–77 at the 2019 survey; n = 29 458; 55% female), 1961–1970 (age 58–67; n = 29 859; 57% female) and 1971–1980 (age 48–57; n = 28 758; 59% female). Data were weighted to align the sample to the Australian population.
Past year meth/amphetamine use; under-reporting of lifetime meth/amphetamine use in each birth cohort, year and survey stratum (operationalised as the difference between self-reported lifetime prevalence in 2001 and that of each subsequent year); proportion of the population who nominated meth/amphetamine as a drug problem in each birth cohort, year and survey stratum. Under-reporting was regressed on the proportion of people holding negative attitude towards meth/amphetamine. Survey year and birth cohort were adjusted for.
Between 2001 and 2019, the lifetime prevalence of meth/amphetamine decreased from 6.1% (95% CI = 5.3–6.9) to 1.7% (95% CI = 1.2–2.2) in the 1951–1960 birth cohort (p < 0.001), from 13.0% (95% CI = 12.0–14.1) to 4.4% (95% CI = 3.7–5.2) in the 1961–1970 birth cohort (p < 0.001) and from 21.4% (95% CI = 19.9–22.9) to 11.2% (95% CI = 10.0–12.4) in the 1971–1980 birth cohort (p < 0.001). The proportion who nominated meth/amphetamine as a ‘drug problem’ increased significantly in all three cohorts (all p < 0.001) and the degree of under-reporting of meth/amphetamine use was significantly associated with proportion of people who nominated meth/amphetamine as the ‘drug problem’ (b = 0.09, SE = 0.01, p < 0.001).
In Australia, the actual prevalence of lifetime meth/amphetamine use may be two- to fourfold higher than that estimated in the most recent national household surveys (2019). The level of under-reporting is strongly associated with increasing negative attitudes towards methylamphetamine and d-amphetamine use over the same period.