“Residual effects of intoxication” refers to any subjective, physiological, and/or behavioral effects of heavy drinking once breath alcohol concentration (BrAC) has returned to zero. Hangover is most accurately defined by symptoms including headache, nausea, and fatigue. We use the term “hangover” to refer to the cluster of symptoms and “residual effects of alcohol” as a broader term covering neurocognitive and occupational impairment in the absence of blood alcohol the morning after intoxication. The causes of hangover are unknown, although several review articles discuss a number of hypotheses. Some portion (25-30%) of the population appears to be hangover resistant across a variety of laboratory, clinical and survey investigations. Little is known, however, about predictors or consequences of resistance to hangover. Hangover resistance was unrelated to gender, age, family history, or average daily volume among heavy drinkers.