Alcohol is a diuretic — it increases the production of urine. These effects occur because alcohol suppresses the production of a hormone known as antidiuretic hormone (ADH), which normally helps our body retain water. Because alcohol-induced diuresis is often out of proportion with the amount of fluid ingested, dehydration can occur. Interestingly, there is very little evidence that electrolyte imbalances contribute to or are associated with hangovers.[1][2]
The lack of a direct causal role of dehydration in hangover is evidenced by the fact that hydration is insufficient to completely resolve hangover symptoms. It should be noted that few studies have investigated the effects of hydration and/or electrolyte supplementation on hangover symptoms. That being said, alcohol-induced dehydration, although distinct from a hangover, does frequently co-occur with a hangover and is very important to treat.[3]