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Although people have suffered from hangovers since ancient times, there is relatively little conclusive scientific research on the exact mechanisms that cause these Sunday-morning miseries. Scientists have found it difficult even to establish a precise definition of "hangover," with most of the literature identifying it vaguely as a group of unpleasant physical and mental symptoms that begin several hours after a person has stopped drinking.  

Widespread consensus among the medical community holds that while we still don't know exactly what causes hangovers, there are probably a number of different mechanisms by which alcohol consumption can make you feel awful the next day. Below we summarize some of the leading hypotheses, but if you really want to nerd out on hangovers, we encourage you to check out the research papers at the bottom of the page, which provide more detail than you'll ever want to know about why you feel so awful after a big night out.

Hangover Symptoms

Physical symptoms of a hangover vary from person to person (and hangover to hangover), but generally include headache, fatigue, nausea or upset stomach, and thirst. Many people also experience rapid heartbeat, tremors, sweating, muscle aches, and increased sensitivity to light and sound.  Mental symptoms such as irritability, depression, and anxiety are also common.


One of the most commonly cited causes of hangovers is dehydration.  Alcohol consumption inhibits the release of an anti-diuretic hormone called vasopressin.  As a result of this suppression, the kidneys do not function properly and the body produces greater amounts of urine, leading to dehydration. Dehydration, which can cause thirst, headaches, weakness, and dizziness, is an important contributing factor for many hangover sufferers, but there are likely a number of other factors at work.

Immune Response

Cytokines are small molecules that the immune system uses to carry messages between cells.  When immune cells detect a pathogen, they secrete cytokines that trigger the body's immune response, like fever or inflammation.  Researchers have found significantly elevated levels of certain cytokines in subjects who are hungover. In separate clinical tests, these specific cytokines have been known to induce flu-like syndromes such as headache, nausea, fatigue, chills, and muscle aches. The overlap with common hangover symptoms and the strong correlation found between hangovers and cytokine concentration in the blood suggest that alcohol interferes with immune functions and that hangovers may at least partly result from the same inflammatory response that the body uses to fight colds and other illnesses.

Alcohol Metabolites

The body metabolizes alcohol by first converting it into acetaldehyde, which can have toxic effects such as headache, nausea, skin flushing, and sweating. In most people, acetaldehyde is rapidly converted into another metabolite called acetate, but some people have a genetic variant that allows acetaldehyde to accumulate in the body and causes them to flush, sweat, and become ill after even a small amount of alcohol. Because of the similarities in acetaldehyde reaction and hangover symptoms, some researchers have postulated that acetaldehyde causes hangovers, despite the fact that acetaldehyde is not present in the blood when the blood alcohol level has reached zero. New research suggests that it is actually the acetate that causes hangover headache, as acetate levels remain elevated in the body for at least six hours after drinking.


Congeners are chemical compound by-products of the alcohol distillation or fermentation process, and give liquors their distinctive flavors, smells, and colors. Darker beverages such as whiskey, brandy, and red wine generally have higher levels of congeners than clearer beverages such as white wine, beer, vodka or gin, which have more pure ethanol. Several experiments have found that bourbon is more likely to produce a hangover than vodka and that the bourbon hangover is more severe. One specific congener that is cited for hangover effects is methanol.  Methanol has a chemical structure that is similar to ethanol, but is metabolized by the body into formaldehyde and formic acid, which are toxic in high concentrations. Because hangovers do occur when pure ethanol is administered, congeners are only part of the hangover equation.  Scientists do not have a good understanding of the mechanism by which congeners impact hangovers, but there seems to be credible scientific evidence supporting the idea that what you drink can have an impact on how you feel the next day. 

Sleep Disturbances

While many people find that they fall asleep more easily after consuming alcohol, a number of studies have found that subjects wake up more often and have decreased REM sleep after drinking alcohol than after drinking a nonalcoholic placebo. Not surprisingly, laboratory measurements of sleep disturbances are highly correlated with severity of hangover symptoms, which implies that at least a contributing factor to hangovers is simply tiredness from poor sleep.  The impact of alcohol on sleep patterns can be compounded by the fact that heavy drinking often occurs on late nights in which total sleep time is reduced, further exacerbating fatigue and drowsiness the next day.

Alcohol Withdrawal

Some researchers have suggested that that a hangover may be partly caused by minor alcohol withdrawal, because there is some overlap in symptoms, particularly the tremors and sweating. The theory is that the nervous system adapts to the sedative effects of alcohol, and then goes into overdrive when the alcohol is removed. This would explain why some people swear by the hair of the dog to cure a hangover, although this remedy just postpones the inevitable.


Given how prevalent hangovers are, the condition has been generally neglected by the medical research community, either because it is entirely preventable (by not drinking alcohol) or because some scientists fear that curing hangovers will encourage excessive drinking. This is beginning to change, and while there is still relatively little known about hangovers, there seems to be consensus that 1) there are a number of mechanisms by which alcohol can make you feel terrible the next day and 2) there is no magic hangover cure that can completely prevent or cure hangovers. 

Based on the research summarized above, the best way to minimize hangovers it to stay hydrated while you're drinking and choose drinks that are low in congeners. If you have a hangover, your best bet is to treat the symptoms with Blowfish, which is formulated with a powerful anti-inflammatory pain reliever (aspirin) and an alertness aid (caffeine) that is delivered in an effervescent solution that is gentle on the stomach.

Scientific Literature

If you're really into the science behind hangovers, here are a few of the most relevant journal articles that are available for free online.  These are just a fraction of what we've gone through, so if you still want more, send us an email.

Alcohol Hangover: Mechanisms and Mediators
Robert Swift, M.D., Ph.D.; and Dena Davidson, Ph.D.
Assesses factors contributing to hangover, evaluates scientific research on various theories.

The Alcohol Hangover - A Puzzling Phenomenon

Joris C. Verster
Reviews scientific research on physiological pathways of hangover.

The Alcohol Hangover

Jeffrey G. Wiese, M.D.; Michael G. Shlipak, M.D., M.P.H.; and Warren S. Browner, M.D., M.P.H.
Review of scientific research on physiological pathways and treatment of hangover.

Intoxication with Bourbon Versus Vodka: Effects on Hangover, Sleep and Next-Day Neurocognitive Performance in Young Adults
Damaris J. Rohsenow, Jonathan Howland, J. Todd Arnedt, Alissa B. Almeida, Jacey Greece, Sara Minsky, Carrie S. Kempler, and Suzanne Sales
Study on effects of heavy drinking with high- or low-congener beverages on next-day neurocognitive performance.

Interventions for preventing or treating alcohol hangover: a systemic review of randomized controlled trials

Max H. Pittler, Joris C. Verster, Edzard Ernst
Assessment of clinical evidence on effectiveness of medical interventions for preventing or treating hangover.

Acetate Causes Alcohol Hangover Headache in Rats

Christina R. Maxwell, Rebecca Jay Spangenberg, Jan B. Hoek, Stephen D. Silberstein, Michael L. Oshinsky
Study on ability of pure ethanol to induce headache in normally-hydrated rats.