When you’re hungover, you might go through your day feeling tired and sluggish or you may be so miserable you can’t get out of bed except to run to the toilet. Most people have experienced a hangover and many people have their own pet theories about what causes them. What do we actually know about what causes hangovers? A few things.
Dehydration. For years, this was thought to be the main driver of hangovers. Many people still believe dehydration and the subsequent imbalance of electrolytes is why they feel so awful the next day. This is why sports drinks are so popular among people who have obviously not just finished exercising. Alcohol does in fact dehydrate you by suppressing the antidiuretic hormone vasopressin, but only a small part of your misery is likely caused by dehydration. It may make your head hurt, and obviously you don’t want to stay dehydrated for long, but other factors appear to be more significant.
Inflammation. This is likely one of the biggest causes of your comprehensive misery. When you drink excessively, your body releases a large number of cytokines. These are immune cells that fight infections and they are the most common marker of inflammation. Basically, when you have this spike in cytokines, your body thinks it has the flu, only there’s no virus. This is what causes much of the lethargy, aches, and nausea.
Stomach irritation. Alcohol is brutal on your digestive tract. Excessive drinking produces more stomach acid and other digestive enzymes. It also slows digestion. This is why your stomach can feel like a train wreck in the morning.
Low blood sugar. Alcohol interrupts the feedback loop that regulates your insulin levels. Normally, if you eat a slice of cake, your body produces insulin, your blood sugar drops, your body sees your blood sugar is normal again and stops producing insulin. When you drink, that process takes much longer, which drives down your blood sugar levels. This is a particular problem if you had dessert or you’re drinking something sweet. You go to sleep and your blood sugar stays low for a long time. When you wake up, you’re irritable, shaky, and disoriented.
Expanded blood vessels. When you’re dehydrated, your body tries to correct it by expanding your blood vessels. When your blood vessels in your head expand, you experience it as a headache.
Congeners. This is the brown stuff in liquor. More congeners seems to correlate with worse hangovers.
Acetaldehyde buildup. Acetaldehyde is a poisonous intermediate product of alcohol metabolism. If you have more than about one drink per hour, your liver gets behind and acetaldehyde starts building up, making you feel terrible.
Hangovers are your body’s way of telling you it doesn’t like what you’re doing to it. When you drink excessively, you’re damaging your body in multiple overlapping ways. The only sure way to avoid a hangover is to not drink.
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Page last reviewed and medically fact-checked | January 29, 2020