While the causes of a hangover are still poorly understood, several factors are known to be involved including acetaldehyde accumulation, changes in the immune system and glucose metabolism, dehydration, metabolic acidosis, disturbed prostaglandin synthesis, increased cardiac output, vasodilation, sleep deprivation and malnutrition. Beverage-specific effects of additives or by-products such as congeners in alcoholic beverages also play an important role. The symptoms occur typically after the intoxicating effect of the alcohol begins to wear off, generally the morning after a night of heavy drinking.
Though many possible remedies and folk cures have been suggested, there is no compelling evidence to suggest that any are effective for preventing or treating alcohol hangover. Avoiding alcohol or drinking in moderation are the most effective ways to avoid a hangover. The socioeconomic consequences and health risks of alcohol hangover include workplace absenteeism, impaired job performance, reduced productivity and poor academic achievement. A hangover may also compromise potentially dangerous daily activities such as driving a car or operating heavy machinery.
An alcohol hangover is associated with a variety of symptoms that may include drowsiness, headache, concentration problems, dry mouth, dizziness, gastrointestinal complaints, fatigue, sweating, nausea, hyper-excitability, anxiety, and a feeling of general discomfort that may last more than 24 hours. Alcohol hangover symptoms develop when blood alcohol concentration falls considerably and peak when it returns to almost zero. Hangover symptoms validated in controlled studies include general malaise, thirst, headache, feeling dizzy or faint, tiredness, loss of appetite, nausea, stomach ache, and feeling as though one's heart is racing. Some symptoms such as changes in sleep pattern and gastrointestinal distress are attributed to direct effects of the alcohol intoxication, or withdrawal symptoms. Drowsiness and impaired cognitive function are the two dominant features of alcohol hangover.
The processes which lead to hangovers are still poorly understood. Several pathophysiological changes may give rise to the alcohol hangover including increased levels of acetaldehyde, hormonal alterations of the cytokine pathways and decrease of the availability of glucose. Additional associated phenomena are dehydration, metabolic acidosis, disturbed prostaglandin synthesis, increased cardiac output, vasodilation, sleep deprivation and insufficient eating. Some complex organic molecules found in alcoholic beverages known as congeners may play an important role in producing hangover effects because some, such as methanol, are metabolized to the notably toxic substances formaldehyde and formic acid.
After being ingested, ethanol is first converted to acetaldehyde by the enzyme alcohol dehydrogenase and then to acetic acid by oxidation process. These reactions also convert nicotinamide adenine dinucleotide (NAD+) to its reduced form NADH in a redox reaction. By causing an imbalance of the NAD+/NADH redox system, alcoholic beverages make normal bodily functions more difficult. Consequences of the alcohol induced redox changes in the human body include increased triglyceride production, increased amino acid catabolism, inhibition of the citric acid cycle, lactic acidosis, ketoacidosis, hyperuricemia, disturbance in cortisol and androgen metabolism and increased fibrogenesis. The metabolism of glucose and insulin are also influenced. However, recent studies showed no significant correlation between hangover severity and the concentrations of various hormones, electrolytes, free fatty acids, triglycerides, lactate, ketone bodies, cortisol, and glucose in blood and urine samples.
Alcohol also induces the CYP2E1 enzyme, which metabolizes ethanol and other substances into more reactive toxins. In particular, in binge drinking the enzyme is activated and plays a role in creating a harmful condition known as oxidative stress which can lead to cell death.