Hangover: what causes it, what really helps and when it becomes an emergency

A hangover is not just dehydration: acetaldehyde produced as alcohol is metabolised, inflammation, fragmented sleep and stomach irritation all contribute, and studies have found no remedy that convincingly shortens it. Time remains the only thing that reliably resolves it, and a rehydration drip can cover the thirst and fluid-loss part, but it does not speed up the elimination of alcohol.

What a hangover actually is

The US National Institute on Alcohol Abuse and Alcoholism (NIAAA) describes a hangover as a set of symptoms that appear after heavy drinking: fatigue, weakness, thirst, headache, muscle aches, nausea, stomach pain, dizziness, sensitivity to light and sound, anxiety, irritability, sweating and raised blood pressure.

There are several causes, and they overlap:

• Mild dehydration. Alcohol inhibits vasopressin, the hormone that signals the kidneys to retain water, so you pass more urine. This probably contributes to thirst, fatigue and headache.
• Fragmented sleep. You fall asleep faster after alcohol, but your sleep breaks up and you wake earlier.
• Stomach irritation. Alcohol directly irritates the stomach lining and increases acid secretion — hence the nausea.
• Inflammation. Alcohol raises the level of inflammation in the body, which contributes to feeling generally unwell.
• Acetaldehyde. The liver converts alcohol into acetaldehyde, a short-lived toxic compound involved in inflammation in several organs.
• Mini-withdrawal. The brain adapts to the calming effect of alcohol, and when it wears off, restlessness and anxiety appear.

A review of studies in volunteers (Penning et al., 2010) found that markers of dehydration, including vasopressin, did not correlate significantly with the severity of the hangover. The most convincing link was with immune factors, and some studies also found a correlation with acetaldehyde. Lack of sleep, smoking and certain components of drinks do not cause a hangover, but they can make it worse.

Dehydration: real, but only one piece of the problem

This is the point most articles miss. Being thirsty in the morning is real, and water helps with thirst. But the NIAAA explicitly notes that research has not found a correlation between the extent of electrolyte imbalances and the severity of the hangover, nor any effect of added electrolytes on severity. In most people, electrolyte balance restores itself once the effect of the alcohol wears off.

In other words: rehydration addresses only one component. Inflammation, acetaldehyde and lost sleep need time.

What helps — and how little evidence there is

Two systematic reviews looked for any intervention that prevents or relieves a hangover:

• BMJ, 2005 (Pittler et al.): eight randomised trials, eight different interventions. Conclusion: there is no convincing evidence that any conventional or complementary intervention is effective. The most reliable method remains abstinence or moderation.
• Addiction, 2022 (Roberts et al.): 21 studies, 386 participants. No two studies tested the same substance, so no meta-analysis could be done, and the quality of all the results was rated as very low.

What can be said in practical terms:

• Water, for thirst and for the mild-dehydration component.
• Rest and time. The NIAAA says it plainly: there is no way to speed up the brain's recovery from alcohol.
• Caution with painkillers. The combination of alcohol and paracetamol can be toxic to the liver, and aspirin and ibuprofen can further irritate the stomach. If you need a painkiller, ask a pharmacist or doctor, and tell them you have been drinking.

The myths, one by one

When it is not a hangover but alcohol poisoning: call 112

Acute alcohol poisoning occurs when the concentration of alcohol in the blood affects the areas of the brain that control breathing, heart rate and temperature. The NIAAA lists the critical signs:

• confusion, stupor;
• difficulty staying awake or being impossible to wake;
• vomiting;
• seizures;
• slow breathing — fewer than 8 breaths a minute — or irregular breathing, with pauses of 10 seconds or more;
• slow pulse, cold and clammy skin;
• dulled reflexes, including no gag reflex;
• very low body temperature, bluish or pale skin.

Do not wait for all the signs to appear. Call 112 (the emergency number). Do not leave the person alone, do not assume they are “sleeping it off”, and if they are unconscious, turn them on their side so they do not choke if they vomit. A cold shower, coffee or walking them around do not reverse the effects and can make the situation worse.

These situations are not solved with a rehydration drip at home. They belong in the emergency department.

What a rehydration drip can and cannot do

What it does not do: it does not speed up the elimination of alcohol. A study in volunteers (Li et al., 1999) gave one litre of saline immediately after drinking and found no difference in the rate of elimination compared with no drip. A randomised trial from 2013, in 144 patients with uncomplicated intoxication who came to the emergency department, compared saline plus observation with observation alone: time spent in hospital, the fall in breath alcohol and intoxication scores were similar. What it can do: it delivers fluids and electrolytes directly into the circulation, without depending on an irritated stomach that sometimes cannot keep down the water you drink. It addresses the thirst and dehydration component — not the inflammation, not the acetaldehyde, not the lost sleep. That is why we do not promise that it “puts you back on your feet”: for relieving the hangover as a whole, there is no evidence.

At Synerva the protocol used is Recovery — rehydration and electrolytes, 350 RON, about 30 minutes, with the medical assessment included. It is given at the clinic or at home, in Bucharest and Ilfov, between 09:00 and 20:00, every day.

The assessment is not a formality. Intravenous fluids call for caution in people with heart or kidney conditions and in older people — the NICE guideline on intravenous fluids recommends smaller amounts and specialist help in these situations. If someone is still heavily under the influence of alcohol, confused or vomiting continuously, we tell them to go to the emergency department; we do not come with a drip.

Prevention remains the only method with evidence

Hangovers get worse as the amount of alcohol increases. Moderation — or not drinking — is, according to both reviews and the NIAAA, the only reliable way to avoid one. Everything else means managing the discomfort until it passes.

Sources

NIAAA — Hangovers (updated December 2025): symptoms, causes, myths, the lack of correlation with electrolytes, the warning about paracetamol.

NIAAA — Understanding the Dangers of Alcohol Overdose: the critical signs of alcohol poisoning and what to do until help arrives.

Penning R. et al. — The pathology of alcohol hangover, Current Drug Abuse Reviews, 2010.

Palmer E. et al. — Alcohol Hangover: Underlying Biochemical, Inflammatory and Neurochemical Mechanisms, Alcohol and Alcoholism, 2019.

Pittler M.H., Verster J.C., Ernst E. — Interventions for preventing or treating alcohol hangover: systematic review of randomised controlled trials, BMJ, 2005.

Roberts E. et al. — The efficacy and tolerability of pharmacologically active interventions for alcohol-induced hangover symptomatology, Addiction, 2022.

Li J., Mills T., Erato R. — Intravenous saline has no effect on blood ethanol clearance, Journal of Emergency Medicine, 1999.

Perez S.R. et al. — Intravenous 0.9% sodium chloride therapy does not reduce length of stay of alcohol-intoxicated patients in the emergency department, Emergency Medicine Australasia, 2013.

NICE — Intravenous fluid therapy in adults in hospital (CG174): caution in kidney or heart failure and in older people.

For information only. It does not replace a medical consultation. If there are signs of acute alcohol poisoning, call 112.