Why does coffee make me sleepy? In studies, caffeine makes people less sleepy on average, so when a cup leaves you drowsy the cause is usually somewhere else. The research points to a handful of separate reasons: going without caffeine, yesterday's late cup, drinking the same dose every day, and plain differences between people.
This post goes through each one, says what the studies measured, and ends with a way to find your own pattern.
Contents
- The short version
- Does coffee itself make you sleepy?
- Reason 1: you are going without
- Reason 2: yesterday's late cup
- Reason 3: the same dose, every day
- Reason 4: bodies differ
- How to find your own pattern
The short version
Caffeine lowers sleepiness in lab studies, and we found no controlled study showing that a normal cup is sedating. Drowsiness is one of the best-documented symptoms of going without caffeine, and it can start 12 to 24 hours after the last dose, which includes the gap between yesterday's last cup and today's first. A cup taken 6 hours before bed still disturbed sleep in one trial, and a worse night means a sleepier day. In regular drinkers, three doses a day for 10 days gave no clear-cut gain in alertness. People also clear caffeine at different speeds. A short log of your last drink, your bedtime and your sleepy moments shows which one applies to you.
Does coffee itself make you sleepy?
In the studies we found, it does the opposite. In a 2013 trial of 369 people, 100 mg of caffeine followed by 150 mg lowered sleepiness in both light and regular drinkers (Rogers et al., 2013).
People also describe a "caffeine crash" after a cup wears off. We did not find a controlled study of that. What the research does show are the four causes below, and they are easier to test than a crash.
Reason 1: you are going without
A 2004 review of 57 experiments and 9 surveys picked out the symptoms of caffeine withdrawal that held up. Ten made the list, including fatigue, decreased energy, decreased alertness and drowsiness. Symptoms typically started 12 to 24 hours after the last dose, peaked at 20 to 51 hours and lasted 2 to 9 days. They appeared even when people gave up as little as 100 mg a day, which is about one mug of instant (Juliano and Griffiths, 2004).
For a daily drinker, a night without caffeine is already a gap of half a day or more. Two studies show how it plays out:
- After an overnight break, the 369 people in the 2013 trial were already doing worse at 10:30am. Later in the afternoon, the ones given placebo were sleepier, less alert and slower on reaction tasks. Caffeine improved those measures in regular drinkers (Rogers et al., 2013).
- In a 2020 study, 20 young men took 150 mg of caffeine three times a day for eight days, then placebo for two. In the late evening of the placebo days they reported more sleepiness, had more attention lapses and showed more signs of sleep pressure on sleep recordings than in the caffeine condition or the placebo-only condition (Weibel et al., 2020).
A 2018 review made the wider point. Part of caffeine's perceived benefit may be the reversal of withdrawal, not a gain over your normal self (O'Callaghan et al., 2018). The hour-by-hour version is in our withdrawal timeline.
If you feel flat before your first cup and fine after it, part of that cup may be bringing you back to normal.
Reason 2: yesterday's late cup
Caffeine's half-life is about 6 hours for most adults, anywhere from 2 to 10. A cup at 3pm is still about half there at 9pm.
A home study gave volunteers 400 mg of caffeine, about four mugs of instant, either at bedtime, 3 hours before or 6 hours before. Compared with placebo, each timing disturbed their sleep, measured by self-report and a portable sleep monitor. The authors concluded that even 6 hours before bed has important disruptive effects (Drake et al., 2013). The Royal College of Psychiatrists advises stopping tea, coffee and anything else with caffeine by 2pm (RCPsych).
When sleep is short, you feel it the next day. A cup changes how sleepy you feel. It does not change how much you slept. The arithmetic is in how long caffeine stays in your system and why your afternoon coffee is keeping you awake.
Reason 3: the same dose, every day
The 2020 study also looked at what daily dosing does to alertness. Volunteers who took 150 mg three times a day for 10 days showed no clear-cut gain in alertness compared with placebo (Weibel et al., 2020). With a steady habit, the same cup does less, and skipping it costs you. We go through that in why caffeine stopped working and caffeine tolerance and how long a reset takes.
Reason 4: bodies differ
If you have ever asked why caffeine doesn't affect you, part of the picture is speed. One liver enzyme, CYP1A2, handles about 95% of the caffeine you drink, and it varies between people. A 2018 review lists age, sex and hormones, liver disease, obesity, smoking and diet as factors that change how fast caffeine is cleared (Nehlig, 2018). Half-life runs from about 2 hours in one adult to 10 in another, so the same cup can fade quickly for one person and hang around for another.
People often describe coffee making them sleepy online, including people with ADHD. We cannot say why it happens for any one person. The research on caffeine and ADHD is thin: a 2023 review of seven small trials in children aged 5 to 15 found no significant benefit of caffeine over placebo for ADHD symptoms, and we did not find a trial in adults with a diagnosis (Perrotte et al., 2023). If you take medicine for ADHD or anything else, tell your GP or pharmacist how much caffeine you have.
How to find your own pattern
For five days, write down three things.
- The time of your last caffeinated drink.
- The time you fell asleep.
- Whether you felt sleepy in the one to three hours after your first cup, and whether you felt flat before it.
Then look at the five days together. A flat start points to Reason 1. A late last drink and a short night point to Reason 2. A habit of the same cups every day points to Reason 3. The caffeine calculator adds up your day in about a minute and shows how much is still in you at bedtime. Nothing needs to change while you log.
If you would rather follow a plan
The Uncaffed 30-day reset kit steps your caffeine down on a fixed schedule:
- Reset takes you from 160 mg a day to none over 20 days, five days at each step, with L-theanine alongside.
- Flow has no added caffeine and runs for all 30 days.
- For the 30 days, the capsules are your only caffeine. Decaf, herbal tea and rooibos keep the ritual going.
Heavy caffeine user? If you have more than about 400 mg a day from all sources, try to cut down a little before you start. Dropping straight to the kit's starting level can be a big change if you're not prepared for it. Not sure how much you have? The calculator adds it up. Everyone else can start straight away.
Preorders are open. Kits ship 30 November, UK only. The quiz helps you find your starting point, and the science page explains how the steps were chosen. The kit is not for under-18s or anyone pregnant or breastfeeding.
