The purpose of this study was to compare alcohol consumption between the heaviest drinking occasion in the period before the coronavirus disease 2019 (COVID-19) lockdown (15 January–14 March 2020) and the first COVID-19 lockdown period (15 March–11 May 2020) in the Netherlands, including the presence and severity of associated hangovers. The analysis included a sub-sample from the “Corona Lockdown: how fit are you?” (CLOFIT) study, comprising N = 761 participants who reported consuming alcohol in 2020. Overall, on the heaviest drinking occasion during the first COVID-19 lockdown period a significant reduction in number of alcoholic drinks consumed on the heaviest drinking occasion, drinking duration, and estimated BAC was observed. A significant reduction was also observed for subjective intoxication and next-day hangover severity. During the lockdown period, a significant reduction in the frequency of alcohol hangovers was reported. Several age and sex differences were observed. Specifically, men consumed significantly more alcohol than women and experienced hangovers significantly more frequently, both before and during the lockdown. With regard to age, young adults (18–35 years old) significantly reduced their alcohol intake on the heaviest drinking occasion during the lockdown and also reported lower ratings of subjective intoxication and hangover severity. No significant changes were seen for individuals above 35 years old. In conclusion, the first COVID-19 lockdown in the Netherlands was associated with reduced alcohol intake on the heaviest drinking occasion and a reduction in the severity of hangovers, particularly among young male adults.