**Background:** The alcohol hangover refers to the combination of negative mental and physical symptoms experienced after a single episode of alcohol consumption, starting when blood alcohol concentration approaches zero. Previous research indicates that 10-20% of drinkers claim not to experience next-day hangovers despite consuming large quantities of alcohol. Most prior studies were limited to single timepoint assessments. This study aimed to comprehensively compare next-day effects between self-reported hangover-resistant and hangover-sensitive drinkers using hourly assessments throughout the day.
**Methods:** A semi-naturalistic study was conducted with 29 healthy volunteers (14 hangover-resistant, 15 hangover-sensitive). Participants were aged 18-30, Dutch, non-smoking, healthy, and not using illicit or medicinal drugs. On the alcohol day, participants consumed alcohol of their choice in naturalistic settings (home, pub, or party). On the control day, no alcohol was consumed. Assessments were made hourly from 09:30 to 15:30, including overall hangover severity (0-10 scale), 23 individual hangover symptoms, Karolinska Sleepiness Scale (KSS), and Profiles of Mood States-Short Form (POMS-SF). Additional morning assessments included State-Trait Anxiety Inventory-Y (STAI-Y), Beck's Depression Inventory-II (BDI-II), RT-18 risk-taking questionnaire, and Groningen Sleep Quality Scale (GSQS). Statistical analyses used non-parametric tests with Bonferroni correction (significance threshold p<0.0071 for multiple comparisons).
**Key Results:** No significant differences were found between groups in demographics, baseline sleep, amount of alcohol consumed, estimated BAC, or total sleep time. Both groups slept approximately 75 minutes less on the alcohol day. For the hangover-sensitive group, overall hangover severity at 09:30 was 6.1 (out of 10), gradually decreasing to 3.2 at 15:30. The most severe symptoms at 09:30 were sleepiness (6.0), fatigue (6.0), concentration problems (5.8), thirst (5.3), nausea (4.5), headache (4.4), reduced appetite (4.3), and clumsiness (4.2). For all timepoints, overall hangover severity ratings of the hangover-sensitive group were significantly higher than those of the hangover-resistant group (p<0.0071). The hangover-sensitive group showed significantly higher KSS sleepiness (peak 7.1 at 09:30) and POMS-SF fatigue (peak 10.3 at 09:30) on the alcohol day, with significantly reduced vigor. In contrast, the hangover-resistant group showed no significant differences between alcohol and control days for most symptoms; average ratings remained below 1 (out of 10) for most symptoms. The only significant finding in the hangover-resistant group was increased fatigue at 10:30 (1.64 vs 0.57) and reduced vigor at 09:30-11:30. Sleep quality on the alcohol day was significantly poorer in the hangover-sensitive group compared to the hangover-resistant group. Regression analyses identified clumsiness, concentration problems, and headache as key predictors of overall hangover severity in the morning and midday, while nausea, vomiting, sleepiness (KSS), and sleep quality were key predictors in the afternoon.
**Clinical Implications:** This study demonstrates that hangovers are not limited to morning hours but persist throughout the day, with symptom severity gradually decreasing but still evident at 15:30 (overall severity 3.2/10). The persistence of symptoms such as sleepiness and concentration problems up to 15 hours after alcohol consumption may have significant implications for daytime functioning, including driving ability and work performance. The findings support that hangover-resistant drinkers experience minimal next-day effects limited to mild sleepiness and reduced vigor, likely related to sleep loss rather than alcohol itself. The study highlights the importance of assessing hangover effects at multiple timepoints and considering individual differences in hangover susceptibility. Future research should investigate the role of alcohol metabolism and inflammatory responses in explaining differences between hangover-sensitive and hangover-resistant drinkers, and assess the impact of alcohol hangovers on daytime performance at different timepoints during the day.