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Background and Aims: Changes in cannabis legalization and availability in Australia necessitate monitoring use and attitudes. We estimated age–period–cohort effects of past‐year cannabis use and attitudes toward criminalization and legalization. Design Analysis of six waves of the Australian National Drug Strategy Household Survey (NDSHS) every 3 years (2001–2016). Setting and participants: The study was nationally representative of Australian households using multistage random sampling, totaling 145 168 respondents 18–79 years old. Data were collected using telephone, face‐to‐face, and drop‐and‐collect. Sample sizes per analysis varied based on data availability (~107 000–127 000 per model). Measurements Six waves of data for past‐year cannabis use (by sex and education), attitudes toward criminalization and legalization. Findings Past‐year cannabis use decreased in young adults ages 18–35 from 2001–2016 (25.1%–18.6%) and increased in middle adults ages 36–55 (8.6%–10.1%) and older adults ages 56–79 (0.6%–3.0%). We observed a positive period effect and negative cohort effect for recent cohorts for past‐year use (e.g. 1955 cohort had 1.41 (95% CI: [1.11, 1.70]) increased log odds vs. 1998 cohort had −2.86 (95% CI: [−3.17, −2.55]) increased log odds) compared with the mean across years. Results were consistent by sex and varied by education. We observed a negative period effect for criminalization favorability (0.14 (95% CI: [0.003, 0.28]) increased log odds in 2001 vs. ‐0.31 (95% CI: [−0.45, −0.17]) increased log odds in 2016) and positive cohort effect for recent cohorts. Last, we observed a positive period effect for legalization support (−0.03 (95% CI: [−0.20, 0.14]) increased log odds in 2001 vs. 0.38 (95% CI: [0.22, 0.55]) increased log odds in 2016) and negative cohort effect for recent cohorts. Conclusion: Cannabis use appears to be increasing in Australia among adults over 35, while decreasing among adolescents and young adults. Legalization support also appears to have been increasing since 2007, signaling discordance between use and attitudes among adolescents and young adults, and potentially predicting increases in use over time. [ABSTRACT FROM AUTHOR]

Background and Aims: As the legal status of cannabis changes across the United States and modes of administration expand, it is important to examine the potential impact on adolescent cannabis use. This study aimed to assess changes in prevalence of frequent cannabis use in adolescents in the United States and how far this varies by age and cohort. Design Analysis of Monitoring the Future, a nationally representative annual survey of 8th‐, 10th‐ and 12th‐grade students in the United States conducted from 1991 to 2018. Setting: In‐school surveys completed by US adolescents. Participants: A total of 1 236 159 8th‐, 10th‐ and 12th‐graders; 51.5% female, 59.6% non‐Hispanic white, 12.3% non‐Hispanic black, 13.4% Hispanic and 14.7% other race/ethnicity. Measurements Frequent cannabis use (FCU), defined as six or more occasions in the past 30 days, stratified by sex, race/ethnicity and parental education. Findings FCU among US adolescents increased over the study period; the peak in 2010–18 was 11.4% among 18‐year‐old students. This increase was best explained by both period and cohort effects. Compared with respondents in 2005, adolescents surveyed in 2018 had period effects in FCU that were 1.6 times greater. Adolescents in younger birth cohorts (those born > 1988) had a lower increase in FCU than those born prior to 1988. Results were consistent across sex, parent education and race/ethnicity, with period effects indicating increasing FCU after 2005 and cohort effects indicating a lower magnitude of increase in more recent birth cohorts. Age and parental education disparities in FCU have increased over time, whereas race/ethnicity differences have converged over time; black students were 0.67 [95% confidence interval (CI) = 0.64–0.70] times as likely to use cannabis frequently as white students from 1991 to 2000, and 1.03 (95% CI = 0.98–1.09) times as likely from 2011 to 2018 (P‐value for time interaction < 0.001). Conclusions: The prevalence of frequent cannabis use (FCU) increased from 1991 to 2018 among older adolescents in the United States. Racial/ethnic differences in FCU converged, whereas parental education differences have diverged. [ABSTRACT FROM AUTHOR]