How long does caffeine stay in your system?

If you're reading this in bed with the afternoon coffee on your mind, it may help to know that it's leaving you even now. The body clears caffeine steadily, about half of it every three to six hours⁵5 Gardiner et al., 2025b in most healthy adults, so there's a little less of it with every hour you lie here. Worry about sleep can stir up a wakefulness of its own⁶6 Harvey, 2002, just when your body is ready to drop off. There's nothing you need to work out tonight. The coffee question can wait for tomorrow afternoon, when you can do something with it.

From the moment you wake, a substance called adenosineadenosine A natural substance in the brain that helps to regulate sleep and is thought to add to the need for sleep when we stay awake for longer than usual. Caffeine works by blocking the places in the brain where adenosine acts. gathers in the brain⁵⁷5 Gardiner et al., 2025b7 Reichert et al., 2022, and the more of it there is, the sleepier you get. This slow build through the day is what researchers call sleep pressuresleep pressure The body’s need for sleep, which builds the longer we stay awake and eases while we sleep., and a night's sleep clears it away again. Caffeine blocks the places where adenosine would act⁵⁷, so the brain stops hearing how tired it is.

That's why the first cup can feel like getting yourself back more than gaining something extra. In people sleeping their usual amount, caffeine mostly restores the alertness that sleepiness had taken away⁸8 Roehrs & Roth, 2008, and does little to lift anyone above their ordinary best. The adenosine is still there all the while, so when the caffeine fades, the tiredness it was covering is waiting to be felt.

Caffeine leaves the body by halves, a little at a time. Its half-lifehalf-life The time it takes the body to clear half of something, such as caffeine. After one half-life, half is left; after two, about a quarter. is the time it takes to clear half of what you had. In healthy adults that is typically three to six hours⁵5 Gardiner et al., 2025b. Small studies of healthy volunteers have measured averages of about five hours¹²⁹1 Jeppesen et al., 19962 Healy et al., 19899 Abernethy & Todd, 1985. Worked out from that average, a coffee at 4pm still has a little more than a third of its caffeine in you at 11pm. A coffee at 8am is down to about an eighth by then.

Around those averages, people vary so widely that published advice on when to stop has ranged from four to eleven hours before bed¹⁰10 Drake et al., 2013. The measured figures come from small groups of healthy volunteers, eight or ten at a time, and your own body may clear caffeine a good deal faster or slower than theirs did.

Perhaps you know someone who can drink an espresso after dinner and sleep soundly, while a cup at three keeps you awake. Part of the difference is that bodies clear caffeine at very different speeds. The liver's main caffeine enzyme works five to six times harder in some people than in others¹¹11 Grzegorzewski et al., 2021, and much of that difference is inherited. Which genes matter is still uncertain⁵¹²5 Gardiner et al., 2025b12 Rétey et al., 2007, and a gene test doesn't yet predict your sleep. Paying attention to how you wake will tell you more.

The birth control pill slows caffeine down too. In one small study, women on the pill took about eight hours to clear half their caffeine, against five and a half⁹9 Abernethy & Todd, 1985 in women not taking it. Fifty years of studies find the same slowing¹¹, so if you take the pill, an afternoon cup is likely to stay with you longer.

Pregnancy stretches it further still, and the slowing begins early³¹¹3 Knutti et al., 1982. In the last four weeks, one study measured a half-life of about ten and a half hours³. If you're pregnant, the NHS advises no more than 200 milligrams a day¹³13 NHS, 2026c, about two cups of instant coffee, because more has been linked to a higher chance of miscarriage and stillbirth. Liver disease slows caffeine as well, most of all cirrhosis¹¹, so if you live with it, your cups will last longer too.

Smoking works the other way, speeding caffeine through the body¹¹, which is why stopping can bring a surprise. Researchers followed twelve people who smoked twenty or more cigarettes a day as they stopped all at once. Their clearance of caffeine fell by about a third¹⁴14 Faber & Fuhr, 2004. Most of that change came in the first few days, and from then on the same coffee stayed in them longer. If you've recently quit and your usual cup seems stronger, this may be part of the reason.

A new prescription can change what your afternoon cup does, because a few medicines keep caffeine in the body far longer. The clearest case is the antidepressant fluvoxamine. Researchers gave it to eight healthy volunteers for twelve days and watched caffeine's half-life stretch from five hours to thirty-one¹1 Jeppesen et al., 1996. That was long enough for them to warn of caffeine intoxication. Fluvoxamine was the only antidepressant they tested, so the finding says nothing either way about others.

Three antibiotics are worth checking your medicine against too. A review of many medicines singled out pipemidic acid and norfloxacin¹¹ alongside fluvoxamine. Ciprofloxacin slows caffeine by less: in ten healthy men it took the half-life from about five hours to about eight²2 Healy et al., 1989. If you take any of these, a pharmacist can help you judge how much caffeine is sensible alongside it.

In a 2013 study, twelve healthy adults slept in their own beds after swallowing a pill that held either caffeine or nothing, without knowing which. On one of the nights the pill held 400 milligrams, a large dose and more than most coffee-shop coffees hold¹⁶16 McCusker et al., 2003, and they took it six hours before bed. A headband measured more than an hour less sleep¹⁰10 Drake et al., 2013 that night. The sleepers' own diaries didn't register the disruption¹⁰.

In 2025 a larger trial followed twenty-three young men at home. One ordinary cup's worth, 100 milligrams, made no measurable difference to their sleep even four hours before bed⁵5 Gardiner et al., 2025b. The large dose of 400 milligrams was another matter: it thinned deep sleepdeep sleep The slowest, most settled stage of sleep, when it’s hardest to wake someone. Most of it comes in the first part of the night. even when it was taken with breakfast, twelve hours before bed⁵. The men felt their sleep was worse only when that dose came four hours before bed, so the breakfast dose did its work unfelt. When the researchers asked, fewer than one in four⁵ could say both how much they'd been given and when. It was the same blind spot the 2013 sleepers had. Women, older adults and people with insomniainsomnia Trouble falling asleep, staying asleep or waking too early, that keeps happening and affects how you feel or get on during the day. have scarcely been studied¹⁰¹⁵15 Clark & Landolt, 2017 in trials like these, and older people's sleep may be more sensitive¹⁵.

So both things can be true at once: you fall asleep easily, and the caffeine is still taking some of the deepest part of your night without your noticing. It can feel as though the tiredness and the coffee feed each other, a thinner night leading to a groggier morning and a stronger urge for the afternoon cup. In one lab study, young men taking caffeine every day woke feeling more tired and found waking harder¹⁷17 Weibel et al., 2021 than on placeboplacebo A dummy treatment, such as a pill with nothing active in it. Studies compare a real treatment against one to see how much of the effect comes from the treatment itself.. A cycle like that is plausible, though it hasn't yet been shown⁵¹⁷.

If there's a cup in your hand in the middle of the afternoon, tonight is probably what you're wondering about. For one ordinary cup, the evidence points to somewhere between about four and nine hours before bed. A large dose needs longer⁵¹⁰5 Gardiner et al., 2025b10 Drake et al., 2013.

What's odd is that the same research group came up with both ends. First they pooled many studies, most of them lab work with doses and timings all over the place, and estimated that a standard coffee of about 107 milligrams would need almost nine hours⁴4 Gardiner et al., 2023 to leave sleep untouched. Then they gave twenty-three young men one ordinary cup at home, and at four hours it made no measurable difference⁵. So which do you believe? The fairest reading is that the real cut-off for one cup is somewhere in that span and moves from person to person, which is why a time tried against your own mornings tells you where yours falls.

The familiar advice to stop about six hours before bed is older. It goes back to the 2013 home study, whose authors suggested finishing substantial caffeine before 5pm at the latest¹⁰.

You may have seen 400 milligrams a day given as a safe amount. The FDA cites it, about two to three 12-ounce cups of coffee¹⁹19 US Food and Drug Administration, 2024, as an amount not generally linked to harm in healthy adults, while noting how widely people differ. The figure comes from a 2017 review²⁰20 Wikoff et al., 2017 sponsored by an industry-funded nutrition science body²¹21 Doepker et al., 2018, whose authors weighed effects on the heart, bones, pregnancy and more. Sleep wasn't among them. In the 2025 trial, 400 milligrams taken in one dose with breakfast still thinned deep sleep twelve hours later⁵.

Across your own day, the caffeine adds up from more than the coffee. Tea, cola and chocolate all count. A coffee-shop cup can hold several times what an instant one does: where a cup of instant coffee holds about 100 milligrams¹³13 NHS, 2026c, one 16-ounce coffee-shop drink bought on six different days ranged from 259 to 564¹⁶16 McCusker et al., 2003.

Caffeine is also added to some painkillers, which is easy to miss. Trials of these combinations used about 100 to 130 milligrams a dose²²22 Derry et al., 2014, about a cup of coffee, so a headache tablet late in the afternoon is worth counting, and its label will tell you what's in yours. It turns up, too, in gum, energy bars, supplements and pre-workout products¹³¹⁹.

You can make this change at your own pace. Two medicines are the exception, and with them it's worth planning with someone first. If you take lithium, please talk to your prescriber before changing how much caffeine you have, because case reports suggest that cutting it sharply may raise lithium levels²³²⁴23 Jefferson, 198824 Frigerio et al., 2021 and bring on tremor. If you take clozapine, which shares caffeine's enzyme, the same conversation with your prescriber is worth having first: in seven patients, five caffeine-free days lowered clozapine levels by about a third to a half²⁵25 Carrillo et al., 1998, and they rose again when caffeine came back.

If you've tried stopping before and had a miserable few days, that was real. Caffeine withdrawalcaffeine withdrawal The headaches, tiredness and low mood that can follow when someone who has caffeine most days stops suddenly. It usually passes within two to nine days, and it isn’t considered dangerous. brings a headache to about half of people²⁶26 Juliano & Griffiths, 2004 in experiments, along with tiredness, low energy, poor concentration and low mood, and it can follow stopping as little as 100 milligrams a day. It usually begins twelve to twenty-four hours after the last cup²⁶, is at its worst within a day or two and has passed within two to nine days. The FDA suggests cutting back gradually¹⁹19 US Food and Drug Administration, 2024: withdrawal isn't dangerous, though it can be unpleasant. You might swap one cup at a time for decaf. That way you keep the warm cup and the pause in the afternoon, while the caffeine in it grows smaller.

What a cup does tonight comes down to its size, the hour you drank it and your own body. A cup of instant coffee at lunchtime is mostly gone by bedtime. A large coffee-shop cup at four still has a good share left in you at 11pm. The cut-off that suits you is personal, and it can move: a pregnancy, a new prescription or your last cigarette would each call for an earlier one. For today, it's enough to notice the size and the hour of the cup in your hand, and see how you wake tomorrow.