How Long Does Caffeine Last? Half-Life, Sleep, and Withdrawal

We have been roasting, brewing, training with, and selling coffee for years, but surprisingly know very little about the substance that makes it interesting to most people: caffeine. I wanted to change that and spoke with Dr. Carolin Reichert, deputy head of the Center for Chronobiology in Basel. She has been researching for almost twenty years how caffeine and adenosine control our sleep, and also works as a psychotherapist.

Her first answer to almost every question was: "it's individual." Her second: "there's no evidence for that." What caffeine actually does to us, what might be perceived truths, and where Carolin Reichert finds us all somewhat careless, I'll clarify in this article.

What caffeine does in the brain: blocking adenosine, not providing energy

Caffeine doesn't give us energy, but blocks the signal that tells us we're tired.

Adenosine is responsible for this. Reichert clarifies a distinction that often goes wrong: "Adenosine is not a hormone, we call it a neuromodulator or sleep factor." It accumulates during the day and docks onto receptors. Caffeine sits on the same receptors.

So the fatigue is still there, we're just not being told about it. This also explains why it comes back once the caffeine is broken down.

In research, two receptor subtypes are relevant, and they do different things. The A2A receptor is where the wake effect occurs: in mice without the A2A receptor, caffeine no longer had a waking effect, but in mice without the A1 receptor, it did. The A1 receptor, on the other hand, is responsible for building up and breaking down the so-called sleep pressure. At usual doses, caffeine only partially occupies the adenosine receptors, estimated at 25 to 50 percent, and not selectively.

Half-life: on average five hours, individually two to ten

Caffeine is absorbed through the gastrointestinal tract. Around 99 percent is absorbed within 45 minutes, with peak levels occurring between 15 and 120 minutes depending on the person.

After that, breakdown begins, which also varies individually. The mean value for healthy adults is around five hours, with a range of 1.5 to 9.5 hours. An independent measurement series found half-lives between 2.27 and 9.87 hours at 5 mg per kilogram of body weight.

Half-life means: after this time, half is gone. With an espresso containing 70 mg at 4 p.m., at five hours' half-life, there are still 35 mg in the blood at 9 p.m., around 17 mg at 2 a.m. For a slow-metabolizing person with a 9.5-hour half-life, the same espresso is still at around 34 mg at 2 a.m., which is double.

Institute of Medicine 2001; Temple et al. 2017; Evans et al., StatPearls 2024; Blanchard & Sawers 1983.

Who metabolizes fast and who slowly: a gene plays a role

An enzyme called CYP1A2 is almost entirely responsible for the breakdown, but it works at different speeds. A difference of up to sixty-fold in metabolic rate was measured between individual people.

One contributing factor is a gene variant called rs762551. Those with two A variants metabolize quickly, those with one or two C variants metabolize slowly. In the population, this is distributed roughly as follows: 40 percent fast, 50 percent mixed, 10 percent slow.

This is why experience reports in comment sections diverge so widely. Reichert: "Some people react almost not at all to caffeine and others react very strongly." And further: "The mechanism of action, that receptors are blocked from this adenosine system, will be the same in all people. But once we look at the effects and see how strongly it affects sleep, performance, mood, motivation, it's very different."

And what about age?

Here we couldn't confirm a widely repeated statement. "Caffeine sensitivity increases with age" is found on many health portals without study references. However, this has been refuted: a comparative study with young and elderly men concluded that "most aspects of the pharmacokinetic behavior of caffeine are very similar in young and elderly men." And the only age-comparative study on sleep EEG we found points in the opposite direction: after 200 mg of caffeine, changes in REM sleep were significant only in the young, not in the middle-aged.

How long does caffeine affect sleep? The numbers

Here we have hard figures. A 2023 meta-analysis compiled what caffeine does to sleep:

Gardiner, Weakley, Burke et al. 2023, Sleep Medicine Reviews 69:101764.

Interesting is the accompanying calculation: for every additional hour of distance to bedtime, sleep loss drops by 2.8 minutes, per milligram of dose it increases by 0.2 minutes.

Deep sleep is the most important value here. 45 minutes less sleep you notice, eleven minutes less deep sleep you don't. Both are measurable, you only feel one of them.

The last coffee: dose beats timing

The question of how many hours before sleep the last coffee should be is the most frequently asked on this topic. The best answer comes from a controlled study from 2025 in which 23 healthy men received 100 mg and 400 mg of caffeine each 12, 8, and 4 hours before bedtime, double-blind and placebo-controlled, with sleep measurement at home.

Gardiner, Weakley, Burke et al. 2025, Sleep 48(4):zsae230. 23 healthy men, 25.3 ± 5.0 years.

The study's conclusion in the original: "A 100 mg dose of caffeine can be consumed up to 4 hours prior to bedtime, but 400 mg may negatively impact sleep when consumed within 12 hours of bedtime."

Translated, this means: a single coffee in the late afternoon is something different from four spread throughout the day. Time alone says little, the amount decides. And 400 mg twelve hours before sleep means that high morning consumption affects the night.

From the 2023 meta-analysis, reference values can be derived, based on a bedtime of 10 p.m.: black tea with 47 mg needs no time limit, coffee with 107 mg needs at least 8.8 hours distance, a pre-workout product with 217.5 mg needs at least 13.2 hours.

Can you fall asleep with caffeine? Yes

Reichert warns against dramatization. In studies where participants had to stay awake for 40 hours while receiving caffeine, "participants could still sleep afterward."

A 2024 study backed this up with numbers. 41 people stayed awake for 38 hours, some received about 350 mg of caffeine twice, the last dose 6.5 hours before recovery sleep. Sleep came in both groups, in both conditions, sleep time exceeded 500 minutes. Caffeine reduced the recovery effect by around 30 minutes and deep sleep by around 36 minutes. Sleep pressure wins, then, but the sleep becomes shallower.

Caffeine withdrawal: headaches in half, from 100 mg per day

This is the part where I'm personally affected. I once drank only decaffeinated coffee for an entire December, my Decaf December, and the headaches of the first week were real. They are also real when I skip coffee in the morning and then notice after a few hours that I have some headaches.

The reference paper on caffeine withdrawal is from 2004 and provides clear numbers:

Juliano & Griffiths 2004, Psychopharmacology 176(1):1–29.

The 100 mg is the most important number in this table. One cup of coffee a day is enough to trigger withdrawal symptoms when stopped. Besides the headache, validated are: fatigue, less energy, less alertness, sleepiness, depressed mood, concentration difficulties, irritability, and a feeling of not being clear-headed.

Reichert mentions the same key symptoms and puts them in context: "This withdrawal syndrome does exist, and it also shows that we have adapted to this chronic consumption that may have occurred before, that the receptor system has adapted to it."

Is there caffeine dependence? No, according to WHO

We keep hearing that coffee is an addictive substance. We would say coffee is a habit. And the technical definition of an addiction is quite different.

The WHO's ICD-11 has its own block for caffeine, 6C48 "Disorders due to use of caffeine". This includes: harmful use as an episode, harmful use pattern, caffeine intoxication, caffeine withdrawal, and caffeine-induced disorders such as an anxiety disorder. What is not in there is a code for dependence. Alcohol, opioids, and stimulants each have one, caffeine does not.

In the DSM-5, it's similar: caffeine intoxication, caffeine withdrawal, and caffeine-induced anxiety and sleep disorders are recognized, but a "Caffeine Use Disorder" is only in the research appendix and not in the diagnostic manual.

Reichert explains why: for dependence, there is a need for loss of control, a strong craving for the substance, and cutting back on family, hobbies, and work. "None of that happens with caffeine." And further: "But what does happen is that you might consume more even though you know it has negative consequences. That harmful use exists, and these physiological adaptations, they happen too."

Tolerance: completely after 18 days, but not for sleep

The body gets used to caffeine, and measurably so. In a study with 300 mg three times daily over 18 consecutive days, caffeine caused no subjective effects in the caffeine group by the end, but it did in the placebo group.

This doesn't apply the same way to sleep. A lab study with 150 mg three times over ten days found no differences in sleep duration, sleep architecture, and sleep efficiency between caffeine, withdrawal, and placebo. However, a large analysis using data from the UK Biobank and home sleep measurements found that at four or more caffeinated beverages per day, sleep time was shortened, with a range of 11 to 229 minutes depending on the model. This range is too wide to cite as a point value, but the direction is clear.

There's another uncomfortable reading, and it's well documented. In habitual consumers who were briefly abstinent, wakefulness after caffeine administration did not exceed that of placebo-treated non-consumers or former consumers. In plain terms: the morning coffee doesn't make many people more alert than normal, it just restores normal.

The cortisol myth: waiting 90 minutes does nothing

I confronted Reichert with a rule, or rather idea, that I hear repeatedly at least in coffee and social media circles: after waking up, wait 60 to 90 minutes, because otherwise the cortisol increase is disrupted and an afternoon slump follows.

What has actually been measured actually flips the story. A study with 96 people gave 300 or 600 mg of caffeine daily over five days and then tested the cortisol response. After abstinence, caffeine triggered a clear cortisol increase. After five days of regular use, the response to the morning dose completely disappeared, in the original "abolished." A residual response remained in the afternoon.

So if you drink coffee daily, you have no cortisol response in the morning that caffeine could disrupt. The rule addresses a group where the described mechanism doesn't exist.

Reichert has another observation on this, and I think it's the more important one: "Of course it's clear that the later I consume caffeine, the longer it's in my body and the later it's broken down." That might be the whole mechanism, which then doesn't need a cortisol narrative anymore.

Placebo and nocebo work in both directions

Part of the caffeine effect happens in the head, and provably in both directions. I had asked whether expectation only strengthens the wake effect. Reichert's answer: "No, also nocebo effects."

Concretely: "If we expect that we can't sleep because we've just had caffeine, then that can keep us awake a bit." She explains it psychologically: "The more tense we are, the more threatened we feel, the less we will fall asleep."

This explains a good portion of the experience reports where a single espresso after lunch supposedly ruined the night. And it has a practical consequence: sleep hygiene rules can become a problem themselves. Reichert on this: "Once you focus too much on these rules and run your life only by them, it becomes a stressor."

How much caffeine is in it?

The numbers vary more than most tables admit. This is especially true for espresso.

Conversions from EFSA 2015, Table 1 (mg/L). Espresso measured values: Crozier, Stalmach & Lean 2012, Food & Function 3(1):30–33. Capsule values: Desbrow, Hall & Irwin 2019, Nutrition and Health 25(1):3–7. Instant coffee: USDA Legacy 2018.

The espresso line is the most interesting in the whole article. In 20 examined establishments, the highest shot was more than six times as high as the lowest, and three out of 20 espressos exceeded the daily recommendation for pregnant women of 200 mg on their own. Bean, grind size, brewing ratio, and cup volume decide more than the drink category. Anyone who wants to know how much caffeine is in their own espresso can find the calculation in the article on double espresso.

On energy drinks, one more correction that Reichert brought up in conversation. First, the amount: "In terms of caffeine, there's often less caffeine in it, usually about eighty milligrams for a small can." Red Bull's manufacturer also states 80 mg for the 250 ml can. A regular cup of coffee is higher. Second, the target group: "It's not that teenagers consume more than adults. Globally or at least in Europe, it shows that teenagers consume about half as much as adults."

How much is too much? The EFSA values

EFSA NDA Panel 2015, Scientific Opinion on the safety of caffeine, EFSA Journal 13(5):4102. The BfR confirms the same values in its Statement No. 037/2026.

There's an important caveat with children and adolescents. The 3 mg per kilogram value is not from a children's study, but an extrapolation from adult data. The EFSA itself writes that "the information available is insufficient to derive a safe caffeine intake." Reichert says the same in different words: "We actually have so little data to even give a guideline on what's tolerable and what's not."

On caffeine intoxication, since that's often asked about. It is a diagnosis in both classification systems, the DSM-5 names a typical triggering dose of significantly over 250 mg plus at least five of twelve symptoms, the ICD-11 names doses over one gram per day. Reichert says: "But I've never heard of a caffeine-induced death." In forensic literature, 92 deaths are documented over 59 years, with life-threatening amounts from about 10 to 14 grams. All documented cases involve tablets, powder, or shots, no coffee. 10 grams equals about 100 cups in a short time at 100 mg per cup.

Reichert names one risk explicitly: "It's more problematic in combination with alcohol, because there are interactions that are unfavorable."

Caffeine and sports: 3 to 6 mg per kilogram, 60 minutes beforehand

The evidence here is better than for almost anything else. The position paper from the International Society of Sports Nutrition from 2021 gives concrete values: caffeine improves performance "consistently" at 3 to 6 mg per kilogram body weight. The minimally effective dose may be 2 mg per kilogram. Very high doses around 9 mg per kilogram bring no additional benefit, just more side effects. The usual intake time is 60 minutes before exertion.

At 75 kilograms body weight, 3 to 6 mg per kilogram is 225 to 450 mg. That's a lot of coffee, and the upper half exceeds the EFSA daily recommendation.

The effects are real, but not spectacular. In time trial performance, a review of 46 randomized studies showed a gain of 2.22 percent, in strength a standardized effect size of 0.18, in muscle endurance 0.30. Caffeine works strongest on aerobic endurance. However, two of the 46 studies showed worsened time trial performance, five showed lower average power.

Caffeine is not banned in sports. It's been on the World Anti-Doping Agency's monitoring program for years, and the 2026 rules continue: "Substances listed in the Monitoring Program are fundamentally not prohibited, but are monitored."

A question from our everyday life

During cupping we slurp coffee and spit it out, a hundred times with the spoon. Do you absorb caffeine that way? Reichert: through the oral mucosa it's basically possible, "for example through caffeine chewing gum." But: "When we drink coffee, surely the bulk is absorbed through the gastrointestinal tract." She doesn't know of studies on retention times in the mouth. In chewing gum research, it takes 44 to 80 minutes of active chewing to reach the active level. With spitting, absorption is probably low, and the tired feeling after a long cupping has other reasons.

And if caffeine is the problem?

Reichert doesn't think caffeine is dangerous: "I don't think it's any kind of devil substance. We would know if it really had serious effects." Her wish is different.

That's our position too, and we have an answer to it in our range. Whoever wants the coffee and doesn't need the caffeine has a real choice today. According to EFSA values, a cup of decaffeinated coffee contains 1.4 to 3.6 mg of caffeine, compared to 80 to 138 mg in filter coffee. The 2025 study showed that 100 mg four hours before sleep had no measurable effect. At three milligrams you don't need to think about the time.

How decaffeinated coffee is made, how it tastes, and why it ages faster and extracts differently can be found in the main article on decaffeinated coffee. You'll find our decafs in the decaf collection.

By the way: caffeine itself is a bitter substance. If you want to know where bitterness in coffee comes from and which part of it isn't tied to caffeine, you'll find that in our article on bitterness in coffee.

To listen to

The full conversation with Carolin Reichert is episode 87 of our podcast.