How to get caffeine out of your system to sleep
You cannot flush caffeine out of your system before bed. The liver clears it at its own pace, about half every 5 to 6 hours, and nothing you drink or do this evening changes that by more than a few minutes. What you can change is everything around it: no more caffeine, less light, a calmer last hour, and tomorrow's cutoff.
People search for a "caffeine flush" because the advice online makes it sound possible. It is not, and knowing that is useful in itself. It saves you the gallon of water at 10 pm and the run around the block, both of which make the night worse.
How much is still in you at bedtime
This is what one drink leaves active at 11 pm, depending on when you had it. Bold figures are above 40 mg, the line Cira uses as low enough to sleep on.
| Had at | Filter coffee (96 mg) | Red Bull (80 mg) | Monster (160 mg) | Diet Coke (46 mg) |
|---|---|---|---|---|
| 2 pm | 33 mg | 27 mg | 55 mg | 16 mg |
| 4 pm | 42 mg | 35 mg | 70 mg | 20 mg |
| 6 pm | 54 mg | 45 mg | 89 mg | 26 mg |
| 8 pm | 68 mg | 57 mg | 114 mg | 33 mg |
A 16 oz Monster at 4 pm still has about 70 mg working at 11 pm, more than a fresh espresso. A mug of filter coffee at the same hour leaves about 42 mg. If your number is above the line, the honest answer is that some of tonight is already spoken for. Try your own drink and hour here:
Try it with your drink
Half-life 5.7 h · peak at 45 min · sleep threshold 40 mg
Why there is no caffeine flush
Almost all caffeine is broken down in the liver, mostly by one enzyme, CYP1A2. Only a few percent leaves the body unchanged in urine. Everything that claims to flush caffeine out works on the wrong organ.
Water. Drinking more raises the volume of urine, not the speed of the liver. It is worth a glass if you are dehydrated, because dehydration makes a racing heart and a headache feel worse. Several glasses late in the evening mostly mean waking at 3 am to use the bathroom.
Exercise and sweating. A workout or a sauna does not clear caffeine faster in any way that moves your bedtime. A gentle walk can give restlessness somewhere to go. Hard exercise is a different matter: a review of evening exercise studies found that vigorous sessions ending within an hour of bed made sleep worse, while earlier or lighter exercise did not.
Food. A meal with the drink slows absorption and blunts the peak. Once the caffeine is absorbed, which for a drink you had hours ago it is, eating changes nothing.
Detox drinks, lemon water, vitamin C and charcoal. There is no good evidence that any of them shortens the time caffeine stays in a healthy adult. Activated charcoal is a hospital treatment given soon after an overdose, before the substance is absorbed. Hours after a coffee there is nothing left in the stomach for it to catch.
A drink to take the edge off. Alcohol makes you drowsy, then breaks up the second half of the night. With caffeine still active that is two disruptions instead of one.
The caffeine you drink at 4 pm is the caffeine you go to bed with. Nothing between 4 pm and 11 pm changes that, so the fix is always earlier in the day.
What actually helps you sleep with caffeine on board
None of this removes caffeine. It removes the other things that keep you awake, which is the part you control.
- Stop now, and check for hidden caffeine. Cola, tea, dark chocolate, pre-workout and some headache tablets all add to the total. The last one of the day is the one still active at bedtime.
- Dim the lights two hours before bed. Bright evening light pushes the body clock later. So does caffeine: in one controlled study, a dose equal to a double espresso three hours before bed delayed the body's melatonin rhythm by about 40 minutes, around half the effect of three hours of bright light. Low light and no bright screens at least avoid stacking the two.
- Keep the last hour calm. A shower, a book, the same routine as other nights. Breathing in for four counts and out for six for a few minutes does not lower caffeine, but it does settle the alarm response that makes a caffeinated night feel worse.
- Do not fight it in bed. If you are still awake after about 20 minutes, get up, do something quiet in dim light, and go back when you feel sleepy. This is stimulus control, one of the techniques the American Academy of Sleep Medicine recommends for insomnia, and it stops the bed turning into the place where you lie awake.
- Keep the room cool and dark. Caffeine keeps sleep lighter, so anything that would wake you from light sleep matters more tonight.
- Get up at your usual time tomorrow. Sleeping in after a short night moves the problem to the next evening. Skip the afternoon nap or keep it under 20 minutes, and do not answer the tired morning with a larger coffee later in the day.
If you are thinking about a sleeping pill or another sleep aid, ask a pharmacist or a doctor first, especially if you take other medicines. That is a question for someone who knows you, not for a website.
How long you actually have to wait
It depends on the dose more than on anything you do. For an average adult, a single espresso falls below 40 mg in about 4 hours, a mug of filter coffee in about 7 and a half hours, a Red Bull in about 6 hours and a 16 oz Monster in about 11 and a half hours.
| Dose | At the peak | After 6 hours | Below 40 mg after |
|---|---|---|---|
| 100 mg | 91 mg | 49 mg | 7 and a half hours |
| 200 mg | 183 mg | 99 mg | 13 and a half hours |
| 300 mg | 274 mg | 148 mg | 17 hours |
| 400 mg | 365 mg | 198 mg | 19 hours |
| 600 mg | 548 mg | 296 mg | 22 and a half hours |
Each dose has its own page, hour by hour, under how long caffeine lasts by dose. If you clear caffeine slowly, from pregnancy, the contraceptive pill or some medicines, add a third or more.
Tomorrow: the only fix that works
The night after a late coffee is rarely ruined by the caffeine you feel. It is the part you do not: in a study where people took 400 mg of caffeine six hours before bed, monitors measured more than an hour less sleep, and the sleepers did not report it. So the fix is not tonight's flush. It is moving the last drink earlier.
Work from your bedtime rather than a fixed hour. For an 11 pm bedtime a mug of filter coffee should be finished by about 3:36 pm, a Red Bull by 5:06 pm and a 16 oz Monster by 11:24 am. The cutoff for your own bedtime is worked out drink by drink, and the guide to when to stop drinking coffee explains the arithmetic. For cans, see how late is too late for an energy drink.
If the problem is not sleep but feeling shaky, sick or wired after too much caffeine, read how to get caffeine out of your system instead. It covers the warning signs that need a doctor rather than a wait.
Sources
- Arnaud MJ. Pharmacokinetics and metabolism of natural methylxanthines in animal and man. Handbook of Experimental Pharmacology, 2011.
- Institute of Medicine. Caffeine for the Sustainment of Mental Task Performance, chapter 2. National Academies Press, 2001.
- Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine, 2013.
- Burke TM, Markwald RR, McHill AW, and others. Effects of caffeine on the human circadian clock in vivo and in vitro. Science Translational Medicine, 2015.
- Stutz J, Eiholzer R, Spengler CM. Effects of evening exercise on sleep in healthy participants: a systematic review and meta-analysis. Sports Medicine, 2019.
- Edinger JD, Arnedt JT, Bertisch SM, and others. Behavioral and psychological treatments for chronic insomnia disorder in adults: an American Academy of Sleep Medicine clinical practice guideline. Journal of Clinical Sleep Medicine, 2021.
Common questions
Can you flush caffeine out of your system before bed?
No. Caffeine is broken down by the liver at its own pace, about half every 5 to 6 hours for a healthy adult, and only a few percent leaves unchanged in urine. Water, exercise, saunas and detox drinks do not change that pace in any way you would notice tonight.
Does drinking water help you sleep after caffeine?
Not by removing caffeine. A glass helps if you are dehydrated, but a lot of water late in the evening mostly means waking up to use the bathroom, which costs sleep rather than saving it.
How long after caffeine can I sleep?
It depends on the dose. A mug of filter coffee (96 mg) takes about 7 and a half hours to fall below 40 mg, the line Cira uses as low enough to sleep on. A Red Bull takes about 6 hours and a 16 oz Monster about 11 and a half hours.
Does exercise get rid of caffeine faster?
Not in any way that matters for tonight. Exercise does not switch on the liver enzyme that breaks caffeine down. A gentle walk can ease restlessness, but hard exercise in the last hour before bed tends to make falling asleep harder, not easier.