Caffeine Half-Life: Why a 3 pm Coffee Is Still in Your Blood at Midnight

Scroll through any sleep corner of social media right now and you will meet the same confident claims: never drink coffee after 2 pm, wait 90 minutes after waking before your first cup, caffeine is “gone” by dinner. Caffeine tracker apps that draw a decaying curve on your phone screen have climbed the download charts, and the phrase caffeine half life has become a search term in its own right. As of mid-2025, the interest is driven less by a single new trial than by a 2023 meta-analysis that put hard numbers on how much sleep a late cup actually costs, and by a wave of creators turning that study into rules.

The rules are catchier than the science. The science is more useful. A half-life is a number, not a guess, and once you understand it you can work out for yourself whether that afternoon latte is still with you when the lights go out. For most adults, it is.

This piece walks through what the half-life means, what shifts it, what the trials actually measured, and where the viral advice is right, roughly right, or simply made up.

What does caffeine half life actually mean?

A half-life is the time it takes for the amount of a substance in your blood to fall by half. It does not mean the substance is half gone and then finished; it means the same halving keeps happening, hour after hour, until the level fades toward zero.

For caffeine in a healthy, non-smoking adult, the average half-life sits at about five hours. The Cleveland Clinic quotes that figure, and the clinical reference text on caffeine in the NIH’s StatPearls series gives a population range of roughly 1.5 to 9.5 hours. That spread matters more than the average. Two colleagues sharing a pot of coffee at 3 pm can be in completely different chemical positions by bedtime, one nearly clear and the other still carrying a third of the dose.

The halving happens because caffeine is broken down almost entirely in the liver by an enzyme called CYP1A2 (an enzyme is a protein that speeds up a chemical reaction). CYP1A2 converts caffeine into three smaller molecules: paraxanthine, theobromine and theophylline. Paraxanthine, which accounts for the bulk of what is produced, is itself mildly stimulating and has its own half-life, so the alertness effect can outlast the parent molecule by a little.

Caffeine is absorbed quickly. Blood levels peak within about 30 to 60 minutes of drinking a cup, which is why the lift arrives fast. The exit is the slow part. If you picture a bathtub with a wide tap and a narrow drain, you have the right model: easy to fill, slow to empty, and the drain narrows further in some people.

One more definition worth fixing early: “wears off” and “cleared” are not the same. The noticeable buzz may fade within three or four hours as your brain adapts, while measurable caffeine lingers far longer. That gap is where the midnight problem lives.

Why a 3 pm coffee is still in your blood at midnight: the math

Run the numbers on a single 8-ounce brewed coffee, which the Mayo Clinic lists at about 96 milligrams of caffeine. Call it 100 for simplicity, and assume a five-hour half-life.

By 8 pm you are down to about 50 milligrams. At midnight, nine hours after the cup, roughly 29 milligrams remain, and it is 1 am before you reach 25. That residual is not trivial: it is about the caffeine in a can of cola, and nobody recommends a cola as a nightcap.

Time after a 3 pm cup	Clock time	Fraction remaining	Approx. caffeine from a 100 mg cup
0 h	3 pm	100%	100 mg
2.5 h	5:30 pm	71%	71 mg
5 h	8 pm	50%	50 mg
9 h	Midnight	29%	29 mg
10 h	1 am	25%	25 mg
15 h	6 am	12.5%	12 mg
20 h	11 am	6%	6 mg
25 h	4 pm next day	3%	3 mg

Assumes a five-hour half-life; real values vary widely between individuals. The table is illustrative, not a diagnostic tool.

Notice the tail. Twenty hours later, a small residue is still present, and if you drink a second coffee the next morning you are stacking on top of it rather than starting from zero. Habitual drinkers who feel they “need” more coffee each year are partly experiencing this layering, partly tolerance.

Now swap the single cup for a 16-ounce coffee-shop drink carrying 200 milligrams or more, or a pre-workout powder taken at 4 pm. The percentages do not change, but the absolute amount at midnight doubles. The half-life tells you the shape of the curve; the dose tells you how high it starts.

What changed recently

The caffeine half life itself has not changed; it is pharmacology, not fashion. What has shifted is the quality of evidence about what the lingering caffeine does to sleep, and how loudly that evidence is being repeated.

The most important recent addition is a 2023 systematic review and meta-analysis (a study that pools results from many earlier studies) published in Sleep Medicine Reviews and indexed on PubMed. Pooling data from 24 studies, the authors found that caffeine consumed during the day shortened total sleep time by about 45 minutes on average, cut sleep efficiency (the share of time in bed actually spent asleep) by around 7 percent, and added roughly 9 minutes to the time taken to fall asleep. The same review calculated that a standard coffee of around 107 milligrams should be finished at least 8.8 hours before bedtime to avoid a measurable effect, and a high-dose pre-workout product about 13 hours before.

That 8.8-hour figure is the number behind the viral “no coffee after 2 pm” rule for people who sleep at 11 pm. The rule is a simplification of a real calculation, which is more than can be said for most trends.

The foundational trial is older. In 2013, researchers published in the Journal of Clinical Sleep Medicine a controlled study in which healthy adults took a fixed dose of caffeine, a placebo, or nothing at zero, three and six hours before bed. Even the six-hour dose reduced objectively measured sleep by more than an hour, and participants were largely unaware of the loss. That last point has aged well; it explains why people insist caffeine does not affect them.

Guidance from the Mayo Clinic, which was updated in 2022 and remains current, still places the upper limit for most healthy adults at about 400 milligrams a day, and the NHS continues to advise no more than 200 milligrams a day in pregnancy.

What the evidence actually says, and how strong it is

Grading the evidence matters here, because the topic attracts both overclaims and dismissals.

Strong evidence (randomized controlled trials): caffeine taken within six hours of bedtime measurably shortens and lightens sleep. The 2013 trial used objective sleep monitoring rather than diaries, which is the gold standard. The 2023 meta-analysis pooled mostly randomized trials and found consistent effects across them. These are the facts you can build habits around.

Moderate evidence (pharmacokinetic studies and observational data): the five-hour average half-life, and the influence of smoking, pregnancy, hormonal contraception and liver disease on it. These measurements come from controlled dosing studies in small groups and are reproducible, but the person-to-person spread is wide, so population averages predict an individual poorly.

Moderate to weak evidence (genetic association studies): that variants in the CYP1A2 gene sort people into “fast” and “slow” metabolizers, and that slow metabolizers report more sleep disruption. The association is real; the clinical usefulness of testing for it is unproven, and no mainstream guideline recommends routine genetic testing to decide when to drink coffee.

Expert opinion or extrapolation: the “90-minute rule” for delaying your first coffee, and precise clock-based cutoffs such as 2 pm. These are reasonable-sounding interpretations of physiology, not tested interventions. No randomized trial has compared waiting 90 minutes with drinking coffee on waking.

Not supported: the claim that caffeine is fully gone within a few hours, or that regular drinkers become immune to its effect on sleep. Tolerance blunts the alerting effect; it does not abolish the sleep effect, and the 2013 participants were habitual users.

If you remember one line: the six-hour cutoff is proven, the longer cutoffs are well-reasoned, and the minute-precise rules are marketing.

How long does caffeine stay in your system, and when does it fully wear off?

The honest answer has two parts, because “in your system” and “wearing off” describe different things.

Chemically, pharmacologists treat a substance as essentially cleared after about five half-lives, when roughly 3 percent remains. For a five-hour half-life that is 25 hours; for a slow metabolizer with a nine-hour half-life it is nearly two days. By that standard, a daily coffee drinker never truly reaches zero, which is why morning blood tests in research studies often still detect caffeine from the previous day.

Functionally, the felt effects follow a shorter arc. Alertness, a faster pulse and the slight tremor some people notice generally peak within the first hour and fade over three to five hours. The subtler effects, lighter sleep and more awakenings, persist as long as a meaningful amount of caffeine is still competing for receptors in the brain, which can be most of the night after an afternoon cup.

The Cleveland Clinic summarizes the practical window as roughly ten hours for most people, meaning that is how long you should expect a typical cup to influence your body in ways that matter. MedlinePlus gives a similar steer: effects can last for hours, and sensitivity varies.

Why do some people drink an espresso after dinner and sleep well? Three explanations, which can overlap. Fast metabolizers genuinely clear the dose before bed. Smokers clear it roughly twice as quickly, because tobacco smoke induces the CYP1A2 enzyme. And some people simply do not perceive their sleep loss, which the 2013 trial showed is common. The espresso drinker who swears it does them no harm may be right, or may have lost an hour of deep sleep they never noticed.

What decides your personal caffeine half life?

The five-hour figure hides a spread that can span a working day. These are the factors with the best evidence behind them.

• Genetics. Common variants in the CYP1A2 gene alter how much enzyme your liver makes. People with the less active variant can carry a half-life toward the top of the range. You cannot change this; you can only time around it.
• Smoking. Compounds in tobacco smoke boost CYP1A2 activity, cutting the half-life by about half. This is also why people who quit smoking often find their usual coffee suddenly feels too strong: the enzyme activity falls back and caffeine lingers.
• Pregnancy. Half-life lengthens steadily, and by the third trimester it can reach around 15 hours according to the StatPearls review. This, together with the fact that caffeine crosses the placenta, underlies the NHS limit of 200 milligrams a day.
• Hormonal contraception. Estrogen-containing contraceptives slow caffeine breakdown, roughly doubling the half-life in some studies.
• Liver disease. Because the liver does nearly all the work, conditions such as cirrhosis can extend the half-life dramatically.
• Age. Newborns lack mature liver enzymes and clear caffeine over several days. In healthy older adults, clearance is only modestly slower, but sleep tends to be lighter, so the same dose costs more.
• Medicines. Certain antidepressants (fluvoxamine is the best-documented), some antibiotics in the quinolone family such as ciprofloxacin, and some medicines used for heart rhythm or stomach acid can slow caffeine clearance. Anyone starting a new prescription who notices unusual jitteriness or insomnia should mention their caffeine intake to the prescriber rather than adjusting the medicine.

Body weight and sex make smaller differences than people assume, once the above are accounted for. What you cannot do is calculate your own half-life from a formula; the only reliable guide is how you sleep after an afternoon cup, measured honestly over a couple of weeks.

Does caffeine affect sleep even if you fall asleep fine?

Yes, and the mechanism explains why the damage is so easy to miss.

Across the day, a molecule called adenosine builds up in the brain as a by-product of cellular activity. Adenosine is the brain’s fatigue signal: the more that accumulates, the sleepier you feel, and the deeper your sleep when it finally comes. Caffeine has a similar shape to adenosine and sits in the same receptors without activating them, like a key that fits the lock but does not turn. Adenosine keeps accumulating behind the blockade, which is why the crash arrives when caffeine fades.

At bedtime, residual caffeine means part of that fatigue signal is still muffled. Many people can still fall asleep, particularly if they are sleep-deprived to begin with. What changes is the architecture of the night. The 2013 trial and the 2023 meta-analysis both recorded less slow-wave sleep (the deepest, most restorative stage), more brief awakenings and lower overall efficiency. Participants’ own ratings of their sleep barely moved; the monitors told a different story.

The consequence is a quiet loop. Lighter sleep leaves you more tired, so you reach for caffeine earlier and in larger amounts, which lightens the next night’s sleep. Harvard Health has described this pattern in its coverage of coffee and health, noting that the most common complaint attached to caffeine is not palpitations or anxiety but disturbed sleep.

A practical experiment takes two weeks and no equipment. Keep your usual morning coffee, move your last caffeinated drink to before 1 pm, and note how often you wake during the night and how you feel at 10 am. If nothing changes, your clearance is probably on the fast side. If it does, you have your answer, and it did not require an app.

What is the 2 hour coffee rule, and what is the 90 minute rule for coffee?

Two rules dominate the current trend, and they refer to opposite ends of the day.

The “2 hour” or “2 pm” rule usually means stop drinking coffee after 2 pm, though some posts phrase it as finishing caffeine at least two hours before bed. The 2 pm version is a rough translation of the 2023 meta-analysis, which calculated an 8.8-hour gap between a standard coffee and bedtime. For an 11 pm bedtime that lands at about 2 pm. For a 9:30 pm bedtime it is closer to 12:45 pm. The rule holds up as a reasonable default; the specific clock time only works if you sleep at eleven. The two-hours-before-bed version is not supported by the evidence, since the 2013 trial showed clear harm from caffeine taken six hours before sleep.

The “90 minute” rule advises waiting about 90 minutes after waking before your first coffee. The reasoning is that cortisol, a hormone that naturally peaks shortly after waking, already provides alertness, and that letting lingering adenosine clear first prevents an afternoon crash. It is plausible physiology. It has not been tested in a randomized trial, and the cortisol peak argument is weak: caffeine’s effects do not depend on where cortisol happens to be. Delaying coffee may help some people feel steadier, especially those who wake at a fixed time every day, but there is no evidence it changes clearance or protects nighttime sleep.

Where the two rules meet is useful. Taken together they define a caffeine window, roughly late morning to early afternoon, that respects the half-life at the evening end and avoids stacking at the morning end. The window is sensible. The minute precision is not.

How much caffeine is really in your cup?

Half-life math is only as good as the starting number, and most people underestimate it. The Mayo Clinic’s reference table gives the following typical values, each with a wide real-world range depending on bean, roast, brew time and serving size.

• Brewed coffee, 8 oz: about 96 mg
• Espresso, single 1 oz shot: about 64 mg
• Instant coffee, 8 oz: about 62 mg
• Decaf brewed coffee, 8 oz: about 2 mg (not zero)
• Black tea, 8 oz: about 47 mg
• Green tea, 8 oz: about 28 mg
• Cola, 12 oz: about 33 mg
• Energy drink, 8 oz: about 72 mg, with 16 oz cans commonly double that
• Energy shot, 2 oz: around 200 mg

Three traps catch people repeatedly. The first is cup size: a “grande” at a coffee chain is 16 ounces, so a plain brewed coffee can deliver 200 milligrams or more, which the Mayo Clinic notes may exceed 300 milligrams in some chains’ larger drinks. The second is pre-workout powders and energy shots, where a single serving can approach a whole day’s recommended maximum and is often taken at 5 pm. The third is hidden sources: dark chocolate, some pain relievers that combine caffeine with other ingredients, and “coffee-flavored” desserts and yogurts.

A rough home audit is worth ten minutes. Write down every caffeinated item from one typical day with its clock time, assign a milligram estimate from the list above, and run the five-hour halving on the last two items. Most people discover that their afternoon total, not their morning cup, is what is still circulating at midnight.

Is it safe to consume 1000 mg of caffeine daily?

No mainstream health authority considers 1,000 milligrams a day a safe routine intake for adults. The Mayo Clinic places the ceiling for most healthy adults at about 400 milligrams a day, roughly four 8-ounce cups of brewed coffee, and that figure is echoed by MedlinePlus. One thousand milligrams is two and a half times that line.

What the evidence shows at that level is fairly consistent. Observational studies and case reports link intakes above the 400 milligram range with a higher likelihood of insomnia, anxiety, a racing or irregular heartbeat, headache, digestive upset, tremor and, in people with a predisposition, panic symptoms. The StatPearls review notes that toxicity symptoms become more common as intake climbs well beyond a gram, and that most reported cases of serious caffeine poisoning involve concentrated powders, tablets or very large volumes of energy drinks rather than brewed coffee, because brewed coffee is self-limiting in a way powders are not.

Half-life makes the picture worse at high doses. If a person takes in 1,000 milligrams spread across the day, the five-hour halving never gets close to clearing the load before the next intake. Steady-state blood levels stay high around the clock, sleep becomes shallow, and the resulting fatigue invites still more caffeine.

Special groups have lower ceilings. The NHS advises people who are pregnant to keep below 200 milligrams a day, and the CDC and NHS both note that caffeine passes into breast milk. Adolescents are generally advised to limit intake sharply, and children to avoid it. People with certain heart rhythm disorders, uncontrolled high blood pressure, anxiety disorders, reflux or migraine often find lower thresholds in practice.

Anyone regularly reaching intakes of this size, especially through powders or tablets, should discuss it with a clinician rather than attempt an abrupt stop on their own, because withdrawal from heavy use can include severe headache and marked fatigue.

Why does caffeine have a half-life but alcohol wears off at a fixed rate?

This question tops search results because it reveals something genuinely interesting about how the body handles different substances.

Caffeine follows what pharmacologists call first-order elimination: the liver enzymes that break it down are nowhere near saturated at normal intakes, so the more caffeine present, the more is processed per hour. Double the dose and the liver roughly doubles its output. The result is a constant fraction removed per unit of time, which is exactly what a half-life describes. The curve is a smooth exponential decay: fast at first, slower and slower as levels fall.

Alcohol is different. The main enzyme responsible, alcohol dehydrogenase, is overwhelmed by even one or two drinks. Once the enzyme is working flat out, it removes a fixed amount per hour regardless of how much more is waiting, which is called zero-order elimination. That is why alcohol metabolism is usually quoted as a rate, roughly one standard drink an hour, rather than as a half-life. The curve is a straight line down, not a decay.

The practical consequences point in opposite directions. With alcohol, having twice as much takes twice as long to clear; the queue just gets longer. With caffeine, having twice as much does not take twice as long to clear, but the lingering tail is proportionally larger, so a big afternoon dose leaves a bigger midnight residue even though the percentage is the same.

There is one caveat. At extremely high intakes, the kind involved in caffeine poisoning, the liver enzymes can approach saturation and caffeine clearance slows further, which is one reason overdoses are more dangerous than a simple halving model would predict. For everyday coffee drinking, the exponential curve holds.

Common myths about caffeine half life, corrected

Myth: caffeine is out of your system in four to six hours. After six hours a little over 40 percent of an afternoon cup remains in a typical adult. Six hours is not clearance; it is roughly one half-life plus a bit.

Myth: regular drinkers are immune to the sleep effect. Tolerance reduces the alerting effect and the jitters. Trials in habitual drinkers still show shortened, lighter sleep, and the 2013 participants were regular users who could not feel the difference.

Myth: decaf is caffeine-free. A cup of decaf typically contains a couple of milligrams, and some decaf drinks from coffee shops contain considerably more. For most people this is negligible; for someone highly sensitive, three decafs after dinner is not nothing.

Myth: a cold shower, water or food will flush caffeine out. Only liver metabolism clears caffeine. Drinking water does not speed it up. Food slows absorption slightly, which can flatten the peak, but does not shorten the half-life.

Myth: a 90-minute coffee delay resets your metabolism. Delaying the first cup may feel smoother for some people, but it does not alter CYP1A2 activity or change how long the afternoon cup lasts.

Myth: you can calculate your exact half-life from an app. Caffeine tracker apps apply a population average, usually five hours, to whatever you log. They are helpful for visualizing stacking and for honesty about intake. They do not know whether you are a slow metabolizer, on hormonal contraception, or a recent ex-smoker, and no app can measure your blood level.

Myth: tea does not count. Tea contains less caffeine per cup than coffee, but it is the same molecule with the same half-life. A large mug of strong black tea at 5 pm is still substantially present at bedtime.

When to stop drinking coffee before bed: a practical timing guide

Evidence supports a tiered answer rather than a single cutoff, because dose and individual clearance both matter.

Six hours before bed is the proven minimum. The 2013 randomized trial showed measurable sleep loss from a substantial dose at that distance. Treat six hours as the line nobody should cross with a full-strength coffee, energy drink or pre-workout product.

Eight to nine hours is the evidence-based default for a regular coffee. That is the 8.8-hour figure from the 2023 meta-analysis for a cup of around 100 milligrams. For a typical 11 pm bedtime, finish coffee by early afternoon.

Twelve to thirteen hours for large doses. The same review suggested about 13 hours for pre-workout products in the 200 milligram range. In practice that means high-dose caffeine belongs with morning training, not evening sessions.

Longer still for slow clearers. People who are pregnant, taking estrogen-containing contraception, living with liver disease, or who have found through experience that afternoon caffeine disturbs them, may do best keeping all caffeine before noon or switching the afternoon cup to a low-caffeine or herbal option.

A few refinements make the guide easier to live with. Shift timing gradually; moving your last coffee an hour earlier each week avoids the withdrawal headache that comes from abrupt change. Replace rather than remove: a decaf or herbal tea keeps the ritual that many people actually crave. And judge the result by how you feel at 10 am, not by whether you fell asleep quickly, since falling asleep is the part caffeine disrupts least.

If sleep stays poor after three or four weeks of keeping caffeine before noon, caffeine is probably not the main problem, and that is worth a conversation with a clinician rather than another round of app tweaking.

When to see a doctor about caffeine, sleep or side effects

Most people can manage caffeine timing on their own. Some situations deserve a clinician’s input, and a few need urgent care.

Seek emergency care for chest pain, a very fast or irregular heartbeat that does not settle, fainting, seizures, repeated vomiting, confusion or severe agitation after caffeine, particularly after powders, tablets, energy shots or multiple energy drinks. Caffeine poisoning is uncommon with brewed coffee but well documented with concentrated products.

Book an appointment if you notice any of the following patterns:

• Insomnia, frequent night waking or unrefreshing sleep that persists for more than a few weeks despite keeping caffeine before noon. Persistent poor sleep can signal sleep apnea, depression, thyroid conditions, restless legs or other treatable problems that caffeine may be masking.
• Palpitations, tremor, anxiety or panic symptoms that began or worsened alongside a new prescription medicine. Several medicines slow caffeine clearance; the prescriber needs to know, and any change to the medicine belongs to them.
• Severe headaches, fatigue or low mood when you try to reduce heavy caffeine use, which can indicate dependence worth managing with support.
• Pregnancy or breastfeeding, where individual advice on intake is appropriate.
• A known heart rhythm disorder, high blood pressure, reflux, glaucoma or a liver condition, since caffeine thresholds may be lower.
• Daytime sleepiness severe enough that you rely on caffeine to drive or work safely. That is a symptom to investigate, not a habit to manage.

Bring a simple log to the appointment: what you drink, how much, at what times, and how you sleep. It is the single most useful thing you can hand a clinician, and it is far more informative than any genetic test or tracker screenshot. Decisions about medicines, including whether a drug interaction with caffeine matters, rest with the prescribing clinician, not with a magazine or an app.

Frequently asked questions

How long does it take for caffeine to fully wear off?

The noticeable buzz fades within about three to five hours, but caffeine is only considered essentially cleared after roughly five half-lives, which is about 25 hours for a typical adult. Slow metabolizers may need closer to two days. Daily drinkers therefore rarely reach zero, which is why morning blood tests in research can still detect the previous afternoon’s coffee.

What is the 2 hour coffee rule?

Most versions mean stop drinking coffee after 2 pm. It derives from a 2023 meta-analysis that calculated an 8.8-hour gap between a standard coffee and bedtime, which lands at 2 pm for an 11 pm sleeper. The rule is a sensible default but the clock time only fits that bedtime. The alternative reading, caffeine until two hours before bed, is not supported by trial evidence.

What is the 90 minute rule for coffee?

It suggests waiting about 90 minutes after waking before your first coffee so the body’s natural morning alertness peak passes and leftover adenosine clears. The idea is plausible but untested in randomized trials, and it does not change how quickly caffeine is cleared later in the day. Some people find a delayed first cup feels steadier; that is a preference, not a proven benefit.

Is it safe to consume 1000 mg of caffeine daily?

No health authority recommends it. The Mayo Clinic and MedlinePlus cite about 400 milligrams a day as the upper limit for most healthy adults, and 1,000 milligrams is well above that. Intakes at this level are linked with insomnia, anxiety, palpitations, tremor and digestive symptoms, and most serious caffeine poisonings involve concentrated powders or tablets. Anyone using this much should talk to a clinician before cutting back abruptly.

How long does caffeine stay in your system if you are a slow metabolizer?

Someone with a less active CYP1A2 enzyme variant can have a half-life of nine hours or more. A 3 pm cup would then still be at about half strength at midnight and a quarter strength the following morning. Pregnancy, estrogen-containing contraception, liver disease and certain medicines push clearance in the same direction. The practical sign is consistently lighter sleep after any afternoon caffeine.

Does caffeine affect sleep even if I fall asleep quickly?

Yes. Residual caffeine blocks adenosine receptors, which mainly reduces deep slow-wave sleep and increases brief awakenings rather than preventing sleep onset. Trials using sleep monitors show these changes in people who reported sleeping normally. Falling asleep fast often reflects sleep deprivation, not the absence of a caffeine effect, so judge your caffeine timing by how rested you feel at mid-morning.

Is a caffeine half life calculator accurate?

Only approximately. Calculators and tracker apps apply a population average, usually five hours, to the amounts you log. They are useful for seeing how afternoon doses stack and for being honest about intake. They cannot know your genetics, smoking status, pregnancy, medicines or liver function, all of which can shift the true half-life by a factor of two or more in either direction.

When should I stop drinking coffee before bed?

Six hours before bed is the proven minimum from randomized trial data, and about eight to nine hours is the evidence-based default for a regular cup. High-dose energy drinks or pre-workout products need around 13 hours. People who clear caffeine slowly, including those who are pregnant or on estrogen-containing contraception, often do best keeping all caffeine before noon.

Does decaf coffee have a half life too?

Decaf contains a small amount of caffeine, typically a few milligrams per cup though some coffee-shop decafs contain more, and that caffeine follows the same five-hour halving. For most people the amount is too small to matter. For someone highly sensitive, or someone drinking several large decafs after dinner, it can still add up to a measurable bedtime residue.

Why do I get a headache when I skip my afternoon coffee?

Regular caffeine use leads the brain to produce extra adenosine receptors to compensate for the blockade. When caffeine is withdrawn, blood vessels in the head widen and the surplus receptors are flooded with adenosine, producing a headache, fatigue and irritability that typically begin within a day and ease within a week. Moving your last coffee earlier by an hour a week minimizes this.

References

• NIH StatPearls: Caffeine
• MedlinePlus: Caffeine

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.