When alcohol is consumed, the pituitary gland in the brain blocks the creation of vasopressin, which means the kidneys send the water straight to the bladder, instead of reabsorbing the water. This can impact your body so greatly that you could expel four times as much liquid as you’re taking in.
Eating fatty foods and carbohydrates before eating slows the absorption of alcohol, which gives your body more time to process it. Also drink lots of water. Some suggest taking two aspirins and drinking a full glass of water before you head to bed. This will keep you hydrated and decrease the severity of the hangover.
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Source: medicalinsurance