Tired, headachy and thirsty after drinking: what's going on?

The tiredness, headache and thirst you feel the morning after drinking are what researchers call a hangover: a set of mental and physical symptoms that starts as the alcohol in your blood approaches zero. NIAAA, the US National Institutes of Health institute for alcohol research, lists several things happening at once: alcohol makes you pass more urine, so you lose fluid; sleep after drinking is broken; alcohol irritates the stomach lining; and it increases inflammation and exposes the body to acetaldehyde, a by-product of breaking alcohol down. In a survey of 1,410 Dutch students, fatigue (95.5%) and thirst (89.1%) were the most common symptoms.

This article explains what is going on in the body. For drinking and blood fats on a health check, see I drink alcohol often. What should I know about blood fats?

What is happening in my body the morning after drinking?

Several processes overlap, which is why the morning after can feel like many problems at once.

How researchers define a hangover

There was long no agreed definition. In 2016, van Schrojenstein Lantman and colleagues at Utrecht University asked 1,099 social drinkers who had recently had a hangover to describe it, then put the draft definitions to an international research group. The agreed definition: "the combination of mental and physical symptoms, experienced the day after a single episode of heavy drinking, starting when blood alcohol concentration approaches zero." NIAAA likewise says symptoms peak when blood alcohol returns to about zero. So the worst of it often comes after the alcohol itself has mostly gone.

What NIAAA lists behind the symptoms

NIAAA adds that darker spirits contain more congeners, other substances made during fermentation, and that sulfites in wine may set off headaches in some people.

Typical symptoms

NIAAA lists fatigue, weakness, thirst, headache, muscle aches, nausea, stomach pain, a spinning feeling, sensitivity to light and sound, anxiety, irritability and sweating among typical symptoms. It notes they can last 24 hours or longer.

Which symptoms are most common the morning after?

The most detailed picture comes from people asked to rate their own last hangover.

A survey of 1,410 students

In a 2012 survey led by Penning and colleagues at Utrecht University, 1,410 Dutch students rated 47 possible symptoms of their latest hangover on a scale of 0 to 10. About half (56.1%) had had a hangover in the past month.

What this tells you

Thirst is very common, but in this survey it contributed much less to how bad the hangover was than feeling drowsy and finding it hard to think clearly. The researchers concluded that drowsiness and impaired thinking are the two main features of a hangover. The survey covered students in one country and relied on memory, so the exact figures may differ for other people.

Why do I wake up early and still feel tired?

Alcohol changes how the night's sleep is built, not just how long it lasts.

What sleep studies show

A 2013 review by Ebrahim and colleagues at the London Sleep Centre brought together sleep-laboratory studies in healthy volunteers. At all amounts studied, alcohol:

• shortened the time it took to fall asleep
• made the first half of the night more settled
• increased disruption in the second half of the night
• delayed the start of dream (REM) sleep

Most of the studies also found more deep sleep in the first half of the night, and at moderate and high amounts, dream sleep made up less of the night overall. In everyday terms, this can look like, for example, dropping off quickly and then waking at 4 or 5 a.m.

Why this matters the next day

NIAAA links fragmented sleep after drinking to tiredness. The NHS says that alcohol can stop you sleeping deeply, and lists feeling better in the mornings and being less tired during the day among the early benefits of drinking less.

For other reasons you might feel drained all day, see Tired, drained and sleepy all day: what causes it?

How long does the body take to clear alcohol?

The body removes alcohol at a fairly steady rate, mainly in the liver, and that rate does not speed up much however much you drank.

The rate from research

A 2010 review by Jones at Sweden's National Board of Forensic Medicine gathered studies that measured how fast alcohol leaves the blood.

The review also found the rate slightly faster in women than in men on average.

Counting what you drank

The NHS describes one unit, 10 ml or 8 g of pure alcohol, as roughly what the average adult can process in an hour. Units are worked out as strength (ABV %) times volume in ml, divided by 1,000. In the US, NIAAA uses a "standard drink" of about 14 g of pure alcohol, so different countries count drinks differently.

The beer figures use the NHS formula. Four large bottles of beer come to about 12 units, or roughly 12 hours of processing by the NHS rule of thumb, and how fast this happens differs from person to person, as the research figures above show.

Driving and work the next morning

NIAAA says that during a hangover, attention, decision-making and muscle coordination can all be impaired, and the ability to drive, operate machinery or care for others can be affected. If you still feel the effects, do not drive.

How much do people in Thailand drink in one session?

Thailand's National Statistical Office runs a national survey of smoking and drinking. Two studies from Thai universities have analysed it.

What the national surveys found

What these numbers can and cannot tell you

The two studies used different definitions of heavy drinking in one session, so their percentages cannot be compared directly. Both are based on what people reported themselves; the Vichitkunakorn study collected answers in face-to-face household interviews. The Sonthon team notes that its figures are likely underestimates, partly because of how the 12-month question was set against the monthly cut-off and because the men's 5-drink cut-off was used for women too. What they show is that a big night out is a common part of life for many Thai drinkers, and that driving afterwards is common too.

What does the NHS suggest for drinking less?

The NHS gives the guidance below to help adults who drink keep their drinking down.

How much, and how often

The NHS advises men and women not to regularly drink more than 14 units a week, to spread it over 3 or more days if they drink that much, and to have several drink-free days each week.

NHS tips for drinking less

When should I get help?

Most hangovers pass with time, but some situations need help.

Get emergency help now

NIAAA lists these danger signs after drinking:

• confusion, or being very hard to wake or unable to stay awake
• vomiting
• seizures
• slow breathing (fewer than 8 breaths a minute) or long gaps between breaths
• a slow heart rate, clammy skin, very low body temperature, or pale or bluish skin

NIAAA notes that blood alcohol can keep rising even after someone stops drinking or passes out, because alcohol in the stomach is still being absorbed. Do not leave the person alone. In Thailand, call 1669 for emergency medical help.

Talk to a doctor or pharmacist

• if you often drink more than you planned, or find it hard to cut down
• if you take regular medicines, ask a doctor or pharmacist whether alcohol affects them
• if you are pregnant or breastfeeding, ask a doctor about alcohol