Module 8 · Sleep & recovery · Strong evidence

Caffeine, alcohol and sleep

Caffeine lingers for hours; alcohol helps you fall asleep and then disturbs the rest of the night.

6 min read · Level: Beginner · Free — no account needed to read

The idea

Caffeine blocks a chemical called adenosine, which builds up during the day and makes you feel sleepy. That is why coffee wakes you up — and why it can keep you up. Caffeine lasts longer than most people think: it takes around five hours on average for half of it to leave your body, and much longer in some people.

In one study, caffeine taken six hours before bed still cut sleep by around an hour, even when people didn’t notice. Many sleep experts suggest stopping caffeine by early afternoon. Remember it is also in tea, cola, energy drinks and some chocolate and medicines.

Alcohol works differently. It can make you fall asleep faster, but it disrupts the second half of the night: sleep becomes lighter and more broken, dreaming sleep is reduced, and you may wake early or need the toilet. It is one of the most common hidden causes of poor sleep.

Why it works

Caffeine and alcohol are two of the easiest things to change for better sleep — and their effects are easy to underestimate because they don’t feel like they are affecting you.

A real example

The situation

Priya has a strong coffee at 4pm and a glass of wine most evenings. She falls asleep fine but wakes at 3am most nights.

What happened

She moves her last coffee to noon and keeps wine to weekends for three weeks. She starts sleeping through most nights and wakes feeling more rested.

The takeaway

Two small timing changes fixed a sleep problem she hadn’t linked to either drink.

Use this when you are…

• you have trouble falling asleep
• you wake in the night or too early
• you rely on caffeine to get through the day

Common mistakes

• Assuming afternoon caffeine doesn’t affect you because you can still fall asleep.
• Using alcohol to help you sleep.
• Forgetting about hidden caffeine in tea, cola and energy drinks.

What the evidence says

Strong evidence: Many good-quality studies, usually including randomised trials and reviews that pool them, point the same way. Guidelines tend to recommend it.

Caffeine’s effects on sleep and its long half-life are well documented, as is alcohol’s disruption of sleep later in the night. How sensitive people are to caffeine varies considerably, partly because of genetics.

Where this comes from: Sleep and circadian research; American Academy of Sleep Medicine (AASM).

Fields that study this: Sleep science, Nutrition science.

Try it now: Find your cut-off

1. Note the time of your last caffeinated drink yesterday.
2. Count back from your bedtime: was it within eight hours?
3. Choose a cut-off time for caffeine this week.

Practise with a guided technique

• Evening wind-down — (20–30 min · Moderate evidence)

Questions to think about

• When do you usually have your last caffeine of the day?
• Have you noticed any link between alcohol and how you sleep?

Try this today

Have your last caffeine before early afternoon today.

Afterwards, ask yourself

What did you notice about your sleep after changing caffeine or alcohol?

Words in this lesson

• Caffeine half-life — The time it takes for half the caffeine you consumed to leave your body — around five hours on average, and longer for some people.