Alcohol and sleep

A glass of wine or a couple of beers in the evening can make it feel easier to drop off. You may also have noticed waking in the small hours after an evening with a few drinks, and finding it hard to get back to sleep. Both come from the same drug, working in two phases through the night.

A sedative with a second half

Alcohol is a sedative: it damps down activity in the brain, which is why you can feel drowsy after a drink. Your liver then breaks it down at a fairly steady rate. The NHS puts one unit (8 g of pure alcohol) at around the amount the average adult can process in an hour, though this varies from person to person. A standard 175 ml glass of 12% wine is about 2.1 units, and a pint of higher-strength (5.2%) lager about 3.

While alcohol is present, the brain is thought to adjust to its damping effect by turning its own alerting systems up to compensate. The most widely held explanation for what happens next is a rebound: once the liver has cleared the alcohol, that adjustment is still running without anything to push against, and the brain swings the other way. Sleep in the second half of the night therefore becomes lighter and more broken, and it's this second phase, not the drowsy first one, that people tend to blame on something else. We're confident about the pattern; the exact wiring behind the rebound in people hasn't been pinned down.

What the research shows

Ebrahim and colleagues (2013) reviewed all the known studies of alcohol and sleep in healthy volunteers. At every dose studied, alcohol shortened the time taken to fall asleep and made the first half of the night more settled, and sleep in the second half became more disrupted. The most consistent effect on REM sleep (the dreaming stage) was that the first REM period of the night arrived later.

A more recent meta-analysis pooled 27 studies in healthy adults (Gardiner et al., 2025). REM sleep was delayed and reduced, starting from a low dose, up to 0.5 g of alcohol per kilogram of body weight (around four UK units for a 70 kg adult), and the effect grew as the amount rose. Falling asleep faster only showed up at high doses, from about 0.85 g per kilogram, or roughly seven units for the same adult, which is a narrower finding than the older review's. This analysis couldn't settle whether alcohol changes total sleep or time awake, because the pooled results were too uncertain.

Some of the clearest evidence for the second-half effect comes from a small laboratory study. Landolt and colleagues (1996) gave ten healthy men in their early sixties about five units six hours before bed. By bedtime there was no alcohol left on their breath, yet they slept less, felt their sleep was more superficial, and spent twice as long awake in the second half of the night as when they'd drunk mineral water. Clearing the alcohol from your blood isn't the same as clearing its effect on your sleep.

Smaller amounts leave a trace too. In 4,098 Finnish employees wearing a chest-strap heart monitor in everyday life, Pietilä and colleagues (2018) compared each person's nights after drinking with their own alcohol-free nights. After a small amount, which on most of those days was a single drink, heart rate was slightly higher and a heart-rhythm measure of recovery was lower in the first three hours of sleep, and the changes grew with larger amounts. It was an observational study based on what people reported drinking, and it measured heart rhythm rather than sleep stages.

What this means for you

The cost of alcohol tends to land late in the night, when you're unlikely to connect it with the drink, and the drowsiness at the start of the night can make it feel helpful. So we judge any change by your diary, which sets your drinks beside your time awake and your morning ratings.

If you drink lightly, one or two units on an evening and under the NHS guideline of 14 units a week, your plan won't usually ask you to change anything. If you're curious, keep the timing of your last drink the same and compare a few alcohol-free nights in your diary with your usual pattern. If you drink most nights or more than 14 units a week, the plan starts by trimming the heaviest nights in small steps, and we'll talk it through with you before anything changes.

Please don't stop drinking suddenly if you drink heavily every day. The NHS warns that stopping suddenly can be very dangerous if you're dependent on alcohol. If you get shaky, sweaty, anxious or sick when you try to cut down, or you find you need a drink to get to sleep, see your GP or an alcohol support service first.