The Mechanism
Alcohol suppresses vasopressin, also called antidiuretic hormone. That hormone normally signals the kidneys to hold on to water. With it suppressed, more fluid is passed than the volume drunk would account for, which is why a night out produces a net loss.
What Dehydration Explains
Thirst, dry mouth, headache and light-headedness map reasonably well onto fluid loss. That is why a glass of water in the morning helps some of what you feel, and why the advice to drink water alongside alcohol is sound as far as it goes.
What It Doesn't
Nausea, poor sleep quality, inflammation and general malaise are driven by other mechanisms, including alcohol's metabolites and its disruption of sleep architecture. No amount of rehydration addresses those, which is why people who drink water diligently through the night still feel unwell.
Where Electrolytes Fit
There is a reasonable case for including some sodium alongside fluid where losses have been substantial, on the same retention logic that applies after sweating. It is not a cure, and the honest summary is that the only reliable variable is how much was drunk in the first place.
Frequently Asked
Does drinking water prevent a hangover?
It can reduce the symptoms driven by fluid loss. It does not address the other mechanisms, so it reduces rather than prevents.
Do electrolyte drinks help a hangover?
They may help restore fluid balance a little more effectively than water alone after significant losses. Claims beyond that are not well supported.
Why am I so thirsty the morning after?
Alcohol suppresses the hormone that tells the kidneys to conserve water, so more fluid is passed overnight than was taken in.
