Introduction: Alcohol-related harms are prevalent late at night, especially on weekends, when high levels of intoxication contribute to increased rates of injury and violence. Reducing or increasing alcohol trading hours late at night in bars and clubs is generally associated with reduced and increased harms, respectively. This study evaluates the impact of later alcohol trading hours in the Scottish cities of Aberdeen and Glasgow on alcohol-related ambulance call-outs and crimes. Under local policy changes, 38 bars in Aberdeen had trading hours extended between 1 and 3 h up to 3am, and 10 nightclubs in Glasgow had a 1-h extension to 4am.

Methods: Following a natural experiment evaluation framework, we used a controlled interrupted time series design to compare outcomes before and after policy changes, from May 2015 to March 2020. The primary outcome was a count of total weekend night-time alcohol-related ambulance call-outs. Secondary outcomes included weekend night-time crimes.

Results: In Aberdeen, the policy led to a significant relative increase of 11.4% (effect size=4.643; 95% CI 0.292 to 8.994; p=0.036) in alcohol-related ambulance call-outs, and 8.5% (effect size=3.442; 95% CI 0.239 to 6.645; p=0.035) in reported crimes, at weekend night-times compared with Edinburgh (control). Findings were not significant and robust across analyses for Glasgow.

Conclusion: Later alcohol trading hours had a significant negative impact on alcohol-related ambulance call-outs and reported crimes in Aberdeen (where more premises had longer extensions) but not in Glasgow, suggesting the number, capacity and type of premises moderated outcomes. This is important for the design of future national and local licensing policies and regulations.