Aims: To estimate change in young people's alcohol consumption during COVID-19 restrictions in Australia in early-mid 2020, and test whether those changes were consistent by gender and level of consumption prior to the pandemic.

Design: Prospective longitudinal cohort.

Setting: Secondary schools in New South Wales, Tasmania and Western Australia.

Participants: Subsample of a cohort (n = 443) recruited in the first year of secondary school in 2010-11. Analysis data included three waves collected in September 2017-July 2018, September 2018-May 2019 and August 2019-January 2020), and in May-June 2020.

Measurements: The primary predictors were time, gender and level of consumption prior to the pandemic. Outcome variables, analysed by mixed-effects models, included frequency and typical quantity of alcohol consumption, binge drinking, peak consumption, alcohol-related harm and drinking contexts.

Findings: Overall consumption (frequency × quantity) during the restrictions declined by 17% [incidence rate ratio (IRR) = 0.83; 95% confidence interval (CI) = 0.73, 0.95] compared to February 2020, and there was a 35% decline in the rate of alcohol-related harms in the same period (IRR = 0.66; 95% CI = 0.54, 0.79). Changes in alcohol consumption were largely consistent by gender.

Conclusions: From a survey of secondary school students in Australia, there is evidence for a reduction in overall consumption and related harms during the COVID-19 restrictions.