Drinking water between drinks did not touch hangover symptoms in a 13-person experiment

Almost everyone has been given this advice, usually by someone confident: have a glass of water between drinks and you will feel better tomorrow. It sounds physiological. Alcohol makes you lose fluid, hangovers involve a headache, headaches respond to water, so the chain seems obvious enough that nobody checks it.

A group in Japan checked it, in Frontiers in Pharmacology. In a controlled experiment with 13 healthy men, they had participants drink at a set pace with or without water alongside, then measured what happened for the next fifteen hours. The water made no difference to anything they could measure.

Why a hangover is not simply dehydration

Alcohol suppresses a hormone that tells the kidneys to hold on to water, which is why a night out involves so many trips to the bathroom. That much is real, and it is where the water advice comes from.

The trouble is that the rest of a hangover does not fit the dehydration story. The headache, nausea and flushing track more closely with acetaldehyde, the toxic compound the body produces while breaking alcohol down, and with the inflammation and disrupted sleep that follow a heavy night. Fluid loss is one strand among several, which is why replacing it might do less than the advice implies.

How the water chaser was tested

The design is a pharmacology experiment rather than a survey, which is its main strength. Participants drank at a constant pace over one hour, with the water group also taking 15 mL/Kg body weight of water intermittently across the same hour. For an average man that is well over a liter, so this was the habit taken seriously.

Then the measurements. Before drinking, immediately after drinking, and at various times up to 15 hours after, the team measured ethanol and acetaldehyde concentrations in the expired air, administered the Digit Symbol Substitution Test, and evaluated the subjective intoxication symptom score. Breath ethanol and acetaldehyde concentrations were determined by sensor gas chromatography.

That covers the three things a hangover remedy could plausibly change: how fast alcohol and its toxic by-product clear, how well the brain works the next day, and how bad you feel.

What the breath alcohol and symptom scores showed

Nothing moved. No differences were observed between the two groups in the kinetics of exhaled ethanol and acetaldehyde, so the water did not speed up or slow down how the alcohol was handled.

The performance test agreed. The Digit Symbol Substitution Test scores were similar between them, which matters because that test is sensitive to exactly the kind of next-day fog people describe.

And the symptoms themselves were unchanged. The subjective ratings covered facial flushing, headache, nausea, concentration, sleepiness, and mood elevation, and no differences were found between the two groups.

Why the water result is less surprising than it feels

Diluting a drink does not change the dose. The body processes a fixed amount of alcohol per hour, largely independent of how much water is in the stomach alongside it, so the exposure that causes the damage is the same either way.

What water does do is slow the drinking down, and that is probably where the folk wisdom comes from. A person alternating water and beer usually drinks less beer. In this experiment the alcohol dose was fixed by the protocol, which removes that effect and isolates the water itself, and once isolated it does nothing.

What 13 people cannot settle about hangovers

The sample is the obvious limit and the authors are direct about it, noting that with a sample size of 13 subjects, the power was barely 0.8 for the effect size they were looking for, so smaller effects could have been missed.

They also flag who was in the room: the participants in this study were all men, so gender differences could not be assessed, and racial differences could not be evaluated either. That matters more than usual for alcohol, because the enzymes that break it down vary between populations, and the study notes that low-activity variants are common among East Asians.

The timing is also narrow. This tested water taken during drinking, which is the specific advice being examined, and says nothing about a pint of water before bed or a morning rehydration drink.

What to do with the water chaser advice

Keep it if it helps you drink less, which is a real benefit by a different route. Drop the expectation that the water itself is neutralising anything.

The uncomfortable version of this result is the honest one: the only reliable way to have a smaller hangover is to drink less alcohol. MedlinePlus is blunt about the arithmetic: drinking less is better for your health than drinking more. A glass of water does not change that arithmetic, and believing it does may make a heavy night feel more manageable than it is.