Hangovers are a group of unpleasant signs and symptoms that can develop after drinking too much alcohol. The causes of hangovers are varied and include:

• Alcohol: Drinking too much alcohol is the main cause of a hangover. Alcohol is metabolized into acetaldehyde, a substance thats toxic at high levels. However, concentrations rarely get that high, so thats not the complete explanation.

• Dehydration: Alcohol suppresses the release of vasopressin, a hormone produced by the brain that sends signals to the kidneys causing them to retain fluid. As a result, alcohol increases urination and excess loss of fluids. The mild dehydration that results likely contributes to hangover symptoms such as thirst, fatigue, and a headache.

• Disturbed sleep: Drinking alcohol disturbs your sleep, causing you to spend less time in the important Rapid Eye Movement (REM) sleep-stage – meaning you wake feeling less refreshed. A late night can mean you get less time in bed before you have to get up too – with some studies suggesting this plays a part in making a hangover worse.

• Inflammation: Alcohol increases inflammation in the body. Inflammation contributes to the malaise that people feel when they are sick, so it may play a role in hangover symptoms as well.

• Acetaldehyde exposure: Alcohol metabolism, primarily by the liver, creates the compound acetaldehyde, a toxic, short-lived byproduct, which contributes to inflammation in the liver, pancreas, brain, gastrointestinal tract, and other organs.

• Low blood sugar: Alcohol can prevent your body from maintaining its usual tight control on blood sugar levels, causing a low blood sugar concentration. Low blood sugar is one of the main causes of fatigue and weakness that people experience as part of a hangover.

• Congeners: Darker colored drinks often contain a high volume of congeners and may be more likely to produce a hangover. Bourbon, whiskey, brandy, and red wine contain high concentrations of congeners, which tend to cause more severe hangovers.

Factors that may make a hangover more likely or severe include drinking on an empty stomach, using other drugs such as nicotine along with alcohol, not sleeping well or long enough after drinking, and having a family history of alcoholism. Drinking plenty of water or soft drinks in between alcoholic drinks can help avoid dehydration, one of the main causes of hangover symptoms.