Aim

To test if (1) there was a change in self-reported lifetime prevalence of meth/amphetamine use by birth cohort and (2) the extent of under-reporting use was associated with the proportion of the population who nominated meth/amphetamine as a drug problem.

Design

Observational study using seven waves of repeated cross-sectional nationally representative household surveys between 2001 and 2019.

Setting

Australia

Participants

Participants were from three birth cohorts: 1951-60 (age 68-77 at the 2019 survey;N=29458;55% female), 1961-70 (age 58-67;N =29859;57% female) and 1971-80 (age 48-57;N=28758;59% female). Data were weighted to align the sample to the Australian population.

Measurements

Past year meth/amphetamine use; under-reporting of lifetime meth/amphetamine use in each birth cohort, year, and survey stratum (operationalized 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.

Findings

Between 2001 and 2019, the lifetime prevalence of meth/amphetamine decreased from 6.1% (95% confidence interval (CI) [5.3, 6.9]) to 1.7% (95% CI [1.2, 2.2]) in the 1951-60 birth cohort (p<.001), from 13.0% (95% CI [12.0, 14.1]) to 4.4% (95% CI [3.7, 5.2]) in the 1961-70 birth cohort (p<.001) and from 21.4% (95% CI [19.9, 22.9]) to 11.2% (10.0, 12.4) in the 1971-80 birth cohort (p<.001). The proportion who nominated meth/amphetamine as a “drug problem” increased significantly in all three cohorts (all p<.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<.001).

Conclusion

In Australia, the actual prevalence of lifetime meth/amphetamine use may be two to four times 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.