Everything you ever wanted to know about hangovers: causes, symptoms, risk factors, consequences and remedies.

The symptoms of hangover

In the scientific literature, hangover is generally described as a malaise manifested by a constellation of biological, physiological and affective symptoms. These can be severe enough to impair function. The discomfort begins when blood alcohol content starts to drop and reaches a peak when it is back to zero. The unpleasantness associated with hangover rarely lasts more than 24 hours.

Hangover symptoms are associated with blood alcohol content, which is determined primarily by three things: time, weight and sex. The distribution of alcohol in the blood is influenced by the ratio of fat to lean tissue in the body, which explains why two people may weigh the same and drink the same amount but have different blood alcohol content. Age is also a factor. Hence, blood alcohol content calculations are approximate.

The most commonly reported hangover symptoms fall into eight main categories:

  1. General effects: fatigue, depression, distress and tremendous thirst
  2. Nociceptive symptoms: muscle pains or cramps, and headaches.
  3. Gastrointestinal disturbances: loss of appetite, stomach ache, nausea, vomiting and diarrhea.
  4. Increased activity in the sympathetic nervous system: increased systolic blood pressure, rapid heart rate (tachycardia), palpitations, tremors and perspiration.
  5. Sensory-perceptual symptoms: dizziness and hyper-sensitivity to sound and light.
  6. Sleep: general reduction in the amount of sleep and, paradoxically, an increase in slow-wave sleep.
  7. Cognitive symptoms: affects attention, concentration and short-term memory.
  8. Psychopathological symptoms: create a deficit in visual-spatial and psychomotor skills, and cause anxiety, depression and irritability.

Excessive drinking assaults just about every part of the body

The causes of hangover

Hangover may well be one of the least-documented alcohol-related subjects. Based on the research to date and an exhaustive review of the biological and medical literature on the subject, it is now possible to group the causes of alcohol hangover into two main categories: indirect and direct. Indirect causes are the dehydration, low blood sugar and sleep disturbance resulting from excessive drinking. The direct cause is the production of acetaldehyde

Dehydration, low blood sugar and sleep disturbance

Excessive drinking assaults just about every part of the body, and organs under attack have to defend themselves. But the body’s physiological defense mechanisms lead to dehydration and low blood sugar. That shortage of water and sugar are what explain the particular discomfort of a hangover.


Obviously, the tremendous thirst associated with hangover is the result of dehydration. So are aching muscles and a throbbing head. When the body is dehydrated, it will draw water from any available source, including the brain. When it does this, the brain atrophies somewhat and the meninges (the protective covering around the brain) shrinks accordingly. The shrinking is what causes the headaches. Dehydration also means a serious loss of electrolytes, which can explain the cramps and muscle pains that generally accompany a hangover.


A significant number of hangover symptoms are also those of hypoglycemia. This is no coincidence. Most of the alcohol a person drinks is processed by the liver, a remarkable organ that, among other things, produces glucose. But the liver can’t make glucose while it’s busy processing alcohol. Glucose is the primary source of energy for metabolism, and the substance most likely to affect the brain. A lack of glucose causes the brain to function abnormally, which is why, for several hours after drinking too much, a person will feel weak, tired, dizzy, anxious and depressed, and have difficulty concentrating and seeing clearly.

Sleep disturbance

Studies have shown that one of the main reasons people feel so poorly the morning after getting drunk is the sleep disturbance caused by excessive drinking. Alcohol makes you sleepy, but it also alters the sleep cycle. Specifically, it can cause insomnia, make you wake up repeatedly during the night and exacerbate sleep disturbances. That’s why people can feel so tired and not in full control of their cognitive capacities the day after heavy drinking. Nobody sleeps well after tying one on.

Acetaldehyde production

As mentioned above, most of the alcohol a person drinks is processed by the liver. In so doing, the liver produces the enzyme alcohol dehydrogenase, which turns the alcohol into acetaldehyde, a very toxic substance. A high concentration of acetaldehyde has a variety of effects on the body, including reddening of the face, sweating, nausea, vomiting and tachycardia (accelerated heart rate). Given the similarity between these symptoms and those of alcohol hangover, some researchers hypothesize that the discomfort of hangover is a direct result of the metabolism of alcohol by the liver.

Risk factors for hangover

Obviously, the primary risk factor associated with alcohol hangover is excessive drinking. The incidence and severity of symptoms increases with the amount of alcohol consumed. That’s why it is so important to remember the low-risk drinking guidelines: on special occasions, women can have three drinks and men, four.

Nonetheless, the incidence and intensity of hangover can vary from one person to the next, even if they drink exactly the same amount. The main risk factors identified to date are listed below.

Congeners and impurities

Separate episodes of alcohol abuse can have different consequences, even if the amount of alcohol is identical. The general consensus among researchers now is that the severity of hangover symptoms can be explained by congeners, i.e. chemical compounds found in alcoholic beverages, such as methanol, histamine or polyphenols.

Similarly, alcoholic drinks that contain high levels of impurities or preservatives may bring on hangover symptoms even when only moderate amounts are consumed. For example, zinc and other metals are sometimes added to alcoholic beverages as artificial sweeteners or to enhance flavour.

Psychological vulnerability

As noted above, about 25% of drinkers never suffer from hangover, no matter how much they drink. Why? Research on the subject is still in its infancy and the phenomenon is still very poorly understood. But one hypothesis is that this may be due to psychosocial factors. Studies by Harburg and his colleagues (1993) have shown a significant connection between drinkers’ psychosocial state and the severity of their hangover symptoms.

The incidence and intensity of hangover symptoms are not due solely to objective causes; they might also be explained by subjective factors distinct to the individual drinker at a particular moment. This may be another reason why researchers note such variations in hangover response from one drinker to the next.

Alcohol and tobacco

The association between episodic drinking and occasional smoking is well known. Many social or weekend smokers develop a sudden and strong urge to smoke when they drink excessively. Similarly, people who have quit smoking often start again during an evening of heavy drinking. These phenomena can be explained by the pharmacological interaction between alcohol and tobacco, which manifests as an intense physical need to smoke.

Consequences and remedies

A hangover is an obvious indication of an episode of abusive drinking. We can therefore conclude that people who report frequent hangovers are at risk for developing the disorders and diseases associated with abusive drinking, all of which are very well documented.

However, little is known as yet about the immediate and long term health effects of hangover. The Alcohol Hangover Research Group has noted the importance of developing methodologies that would eventually allow researchers to obtain reliable measurements of the effects of hangover on the health of drinkers.

Nonetheless, when it comes to reducing the unpleasant symptoms of alcohol hangover, a very specific warning can be issued. Headache is a symptom reported by almost 90% of people suffering from hangover16, but taking acetaminophen (Tylenol) for the pain is not advisable for everyone. Acetaminophen is tolerated by occasional drinkers who may drink too much on a particular occasion, but it is strictly contraindicated for people with an alcohol dependency (alcoholics) who have been diagnosed with liver problems. Clinical studies show that in such cases, the interaction between alcohol and acetaminophen significantly increases the risk of liver toxicity and may cause liver lesions, even when the medication is taken the next day. For some people, therefore, a hangover headache is a “punishment” they just have to live with.

Depending on individual sensitivity, combining alcohol with acetylsalicylic acid (Aspirin) or ibuprofen (Advil, Motrin) may also be a bad idea. Alcohol can cause irritation or even inflammation of the mucous lining of the stomach. In people who are prone to gastro-intestinal problems, these medications can exacerbate the irritating effects of alcohol.

In fact, the only safe way to treat the pain and discomfort of a hangover is to practice healthy living: exercise to increase oxygen supply, rehydrate by drinking plenty of water, and eat lightly. After that, only time will help.

Want to keep an eye on your alcohol intake? The Drink Dashboard helps you track and understand your alcohol consumption over time in terms of health effects, calories and food equivalents.

Alcohol hangover