Hangover: What Is Actually Happening and What Helps

The headache, nausea, thirst and jittery mood of the morning after arrive just as the alcohol in your blood gets close to zero. It is not simply dehydration: poor sleep, an irritated stomach, inflammation, acetaldehyde and a rebound of the nervous system all play a part. No remedy has good evidence behind it; time works, and "hair of the dog" can make it last longer.

When to see a doctor

Right away (999 in the UK, 911 in the US, 112 in the EU): signs of alcohol poisoning, even if it is already morning — confusion, a person who is hard to wake or cannot be woken, slow or irregular breathing, seizures, pale or bluish skin, cold and clammy skin (NHS, UK; NIAAA, US). Alcohol keeps being absorbed after the last drink, so sleeping it off is no guarantee. Stay with the person; what to do while you wait is on how alcohol leaves the body. Also right away: vomiting blood together with confusion, feeling faint or dizzy, fast or shallow breathing, cold pale skin, tummy pain or black stools (NHS). Shaking, hallucinations, confusion or seizures that begin after someone who drinks heavily every day suddenly stops — that is withdrawal, not a hangover, and it can be dangerous (NHS). And any suspicion that you took more paracetamol than the leaflet allows, for example from two products at once: an overdose gives no symptoms for hours (NHS).

The same day: you cannot keep fluids down; you vomited blood, it has stopped and you have no other symptoms — an urgent GP appointment or 111 in the UK (NHS); you are pregnant and worried about what you drank — call your midwife or doctor (the UK Chief Medical Officers consider a little drinking before you knew likely to be low risk).

Routinely: hangovers are frequent; you need a drink in the morning to feel normal; shaking, sweating or anxiety ease only when you drink. In the UK, see your GP or call Drinkline (NHS). If you drink every day, do not stop abruptly without a doctor.

What is happening

Researchers define a hangover as the state the day after heavy drinking, when blood alcohol approaches zero; it can last 24 hours or more (NIAAA, US). Several things contribute:

Poor sleep. Alcohol lowers sleep efficiency and REM sleep and adds wakefulness, so you wake early and sleepy (Rohsenow et al., 2010).
An irritated stomach with more acid — hence the nausea (NIAAA).
Inflammation. Across studies, hangover severity tracks immune markers more convincingly than anything else (Penning et al., 2010).
Acetaldehyde, a toxic, short-lived breakdown product of alcohol (NIAAA).
A mini-withdrawal. The brain adapts to alcohol's calming effect and swings back as it leaves — the source of next-day anxiety (NIAAA).
Congeners, compounds more abundant in dark drinks. Bourbon caused worse hangovers than vodka in a trial, but impaired attention and reaction equally: the drink changes how bad you feel, not how impaired you are (Rohsenow et al., 2010). The order of drinks does not matter; the total does (NIAAA).

Why water is not the cure. Alcohol suppresses the hormone vasopressin, so you pass more urine. Yet markers of dehydration do not correlate with how bad the hangover is (Penning et al., 2010). A 2024 review calls them related but independent consequences of drinking: dehydration is usually mild and brief, water while drinking only modestly lowered the chance of a hangover, and water drunk during the hangover was not linked to its severity (Mackus et al., 2024). When you are vomiting, though, replacing fluid does matter: dehydration and oral rehydration.

Remedies. A systematic review of eight trials found no compelling evidence that any remedy prevents or treats a hangover (Pittler et al., BMJ 2005). A 2022 review of 21 trials, no remedy studied twice, found only very low-quality evidence for any of them (Roberts et al., 2022). Not proof that nothing works — nothing has been shown to.

What to do

Give it time. Rest, food and water if they help — comfort, not treatment.
Coffee and a cold shower do not cure a hangover (NIAAA).
Skip the hair of the dog. Another drink may mask symptoms for a while but can prolong the hangover (NIAAA); needing it is a reason to see a doctor.
Painkillers. The choice depends on your contraindications, how much you drank and how you feel; after a heavy night there is no ideal option. Alcohol with paracetamol (acetaminophen) can harm the liver: the FDA (US) warns about three or more drinks a day, and the NHS (UK) says paracetamol does not suit people who binge drink or are dependent on alcohol. Ibuprofen and aspirin add to the stomach irritation alcohol has already caused (NIAAA). Details: paracetamol or ibuprofen; "hangover" sachets often contain paracetamol too — check the active ingredient.
Do not drive by how you feel. In simulator studies, hungover drivers weaved more and lost attention more often, and in one the impairment was similar whether or not a breathalyser still showed alcohol (Verster et al., 2014; Alford et al., 2020). A zero reading does not mean you are fit to drive.
Next time: drink more slowly, with food, alternating with water (UK Chief Medical Officers); less alcohol is the only reliable way to a lighter morning.

When this is not the case

Pregnancy and breastfeeding: the safest choice is not to drink. Never share a bed or sofa with a baby after any alcohol (NHS).
Medicines: alcohol with sleeping pills, sedatives, opioids or some antihistamines can dangerously slow breathing (NIAAA); check your leaflets.
The mood is part of it: after a short night everything looks more personal; big conversations can wait.
Related: alcohol, honestly — dose, sleep and risk; detox cleanses do not work.

Sources

Checked: 24 September 2026