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All of Your Sleep, Energy, and Caffeine Questions Answered

Caffeine can last in your system for 12+ hours. You should find your cutoff time to drink it and sleep well. More caffeine questions are answered below.
Written by
Jeff Kahn, M.S., Rise Science Co-Founder
Reviewed by
Chester Wu, MD, Rise Science Medical Reviewer
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Sleepy man drinking caffeine

Sleep and caffeine: it’s not a simple relationship. Caffeine can give you energy during the day, but it can also keep you awake at night, compromising your much-needed sleep and next-day energy levels. But that doesn’t mean you have to cut caffeine out of your life altogether. 

That’s good news because caffeine use is common: 90% of American adults drink caffeinated beverages every day. And caffeine has been shown to do everything from boost your memory to protect you from type 2 diabetes, and it can help shake off morning grogginess, too. You just need to get the timing of it right. 

Want to master the art of consuming caffeine? We’ve answered every question you could have about caffeine, sleep, and energy below. Plus, we show you how the RISE app can help you get the sleep you need, even if you drink coffee, and get the energy you want, even if you decide to cut down or cut it out altogether. 

How Does Caffeine Work?

We know caffeine makes us feel more alert, but what exactly is going on behind the scenes? 

When we consume caffeine, enzymes in the liver metabolize it into paraxanthine and theophylline. These compounds then temporarily block the A1 and A2 adenosine receptors in your brain. 

Adenosine is a natural compound that builds up in your body all the time you’re awake. As levels rise, we start to feel more and more tired and we eventually get the urge to go to sleep — this is known as sleep pressure. 

Adenosine acts as a neurotransmitter, depressing the central nervous system and sending messages to the brain to tell it when to rest. But when caffeine has blocked adenosine receptors, adenosine can’t bind to them, meaning the compound can’t make you feel tired.

Caffeine also increases your heart rate and triggers the release of adrenaline and cortisol, making you feel alert and ready for action.  

Caffeine eventually wears off and adenosine can then bind to adenosine receptors again, meaning you start feeling tired. Sometimes you’ll feel even more tired than before, as adenosine has been building up in the background. 

Plus, research suggests people who regularly consume caffeine have more adenosine receptors, making them more sensitive to the compound and its sleepiness effects. 

Caffeine might also affect sleep by an effect on branched-chain amino acids, which are a biomarker of mental fatigue. As described in a 2011 meta analysis, a small study examined levels of amino acids in 17 healthy participants who randomly received 100 mg/day of caffeine or a placebo twice a day for eight consecutive days. Fatigue was induced by mental task performance. Task performance of the caffeine group was better than the performance observed in the placebo group but the subjective perception of fatigue, motivation, and sleepiness did not differ between both groups. However, the plasma branched-chain amino acid levels in the caffeine group were lower than those observed in the placebo group after the fatigue-inducing mental tasks. This may show that caffeine can speed up mental fatigue by activating more of the brain, but without an increased feeling of tiredness. This suggests caffeine may override an innate warning mechanism essential for reducing acute fatigue and might explain why caffeine, particularly when consumed later in the day, might have a detrimental effect on subsequent sleep. 

Caffeine can enhance alertness and performance, and reduce risk of injury or error, when you’re sleep deprived, sleep restricted, or when doing night shift work. But caffeine may not actually be improving your performance, but rather restoring what’s been lost through sleepiness. 

Whether caffeine can boost performance in a non-sleep deprived population is more of an open question than one might imagine. It’s difficult for researchers to measure performance increases in so-called non-sleep-deprived people as so many of us are actually sleep deprived and unaware. We get used to this sleep deprivation and so often don’t even realize our performance impairment. 

What’s more, our circadian rhythm (or body clock) affects how well we perform certain tasks throughout the day, so it’s difficult to tell whether performance increases are coming from caffeine or simply from the time of day we do things.

Enhanced performance may also be in part due to our bodies expecting caffeine, if we’re habitual drinkers, and to the placebo effect. And it may also be down to the reversal of withdrawal symptoms after not having coffee overnight. 

How Long Does it Take Caffeine to Kick in?

Just like with many things with caffeine, how long it takes for it to kick in will depend on your individual biology. It’s thought caffeine is completely absorbed within 45 minutes and it can reach peak levels in your system 15 to 120 minutes after you consume it. 

How Much Caffeine is in Common Drinks?

The amount of caffeine in certain drinks depends on the type of coffee beans (Robusta has more caffeine than Arabica beans), the type of tea leaves (some black teas have more caffeine than green teas), and how the drink is made (light roast coffee can have a slightly higher caffeine content and hotter water when brewing can cause higher caffeine levels, for example).

As a rough guide:

  • Brewed coffee — about 95 milligrams of caffeine per 8-ounce cup 
  • A single shot of espresso — about 63 mg 
  • One cup of instant coffee — 30 mg to 90 mg 
  • Decaf coffee — 3 mg to 12 mg (it all depends on the decaffeination method)  
  • Soft drinks like Coke — 21 mg per 7.5 ounce can  
  • Black tea — 47 mg to 90 mg per 8-ounce cup 
  • Green tea — 20 mg to 45 mg per 8-ounce cup 
  • Energy drink — 50 mg to 160 mg  
  • Milk chocolate — 9 mg per 1.55 ounces 
  • Dark chocolate — 12 mg per ounce 

Heads up: It's much easier to consume more caffeine than we realize! 8 oz. of coffee is the size of just a “Short” cup at Starbucks. Tall, Grande, Venti, and Trenta cups at the popular coffee chain are 12 oz., 16 oz., 20 oz. for hot drinks and 24 oz. for cold drinks, and 31 oz. respectively. If you opt for their signature Pike Place coffee blend, that means you’ll be consuming 155 mg, 235 mg, 310 mg, or 410 mg of caffeine (from Short through Venti). A Trenta iced coffee, meanwhile, has 285 mg caffeine.

How Much Caffeine Can You Have Each Day?

The US Food and Drug Administration (FDA) recommends keeping caffeine intake to 400 milligrams per day, stating this amount isn’t generally associated with negative effects. 

Other research suggests 300 milligrams a day isn't associated with adverse health effects in healthy adults.

If you’re sensitive to caffeine, have certain health conditions like high blood pressure, or are pregnant, you may need to avoid high levels of caffeine.

More research needs to be done into the long-term safety of energy drinks, so experts recommend limiting yourself to one can of energy drink per day.

Be careful you’re not consuming more caffeine than you think you are. Research shows self-reported caffeine consumption is often below actual levels as people tend to only think about coffee and overlook the caffeine in tea, hot chocolate, and energy drinks, for example. And they may not think about decaf coffee, which still has caffeine in it, just in smaller amounts.

Plus, the amount of caffeine in drinks can vary wildly. One paper on the topic listed the caffeine content of one 150-milliliter cup of ground coffee as ranging from 64 mg to 124 mg. Even worse? Instant coffee ranged from 21 mg to 128 mg.  

This is why we recommend focusing on consuming caffeine at the right times, rather than focusing on the right amounts, as it’s hard to tell how much caffeine exactly you’re consuming. 

You can learn more about how much caffeine is too much here.

How Much Caffeine Can You Have When Pregnant?

You may not have to give up caffeine altogether when you’re pregnant.

According to The American College of Obstetricians and Gynecologists, you should limit caffeine to less than 200 milligrams a day. Other research says pregnant women — and those planning on becoming pregnant — should limit consumption to 300 milligrams a day. 

Check with your healthcare provider to make sure it’s okay for you to consume caffeine and how much exactly you should limit yourself to. 

Giving up or cutting down on coffee? You can learn other ways to get energy when pregnant here.  

How Long Does Caffeine Last?

The effects of caffeine last longer than many of us think. As a rough guide, it’s thought that caffeine can last in your system for more than 12 hours. But how long it lasts will depend on: 

  • Age
  • Metabolism
  • Genetics
  • Whether you’re a regular coffee drinker
  • Whether you’re taking medication, including birth control
  • Whether you smoke
  • How much coffee you’ve had that day (the more you have, the more it’ll affect you, and the longer it will take your body to break it all down)

Sleep researchers Dieter Reimann and Christoph Nissen in The Oxford Handbook of Sleep Disorders state that a single dose of caffeine has a half-life of three to seven hours. 

That means it would take three to seven hours for the amount of caffeine in your system to go down by half. And then another three to seven hours for it to go down by half again, and so on. 

One study gave participants 400 mg of caffeine either at bedtime, three hours before bed, or six hours before bed. The results showed that caffeine disrupted sleep at all three times. Even when consumed six hours before bed, caffeine reduced sleep duration by more than one hour. 

So it’s clear, caffeine lingers in your system long after your final sip of coffee. 

When Should You Stop Drinking Coffee to Stop it Impacting Your Sleep?

RISE app screenshot telling you what times to limit caffeine
The RISE app can tell you your caffeine cutoff time each day.

Caffeine can last in your system for 12+ hours, but this number is different for everyone. If you’re sensitive to caffeine, you may need a longer period of caffeine abstinence before bed to make sure it doesn’t keep you up.

RISE predicts the timing of your circadian rhythm, or your internal biological clock, based on factors like how long you slept the night before and your inferred light exposure. The app then tells you your caffeine cutoff time based on when your body naturally wants to go to sleep each night. 

Your caffeine cutoff time is the time you should stop drinking coffee — or anything else with caffeine — to give your body enough time to break it down by bedtime. 

Many people’s cutoff time will be around noon, but night owls may be able to enjoy coffee until about 2 p.m. Check RISE before placing your last coffee order, and opt for caffeine-free drinks after your cutoff time. 

You can learn more about when you should stop drinking coffee here. 

RISE users on iOS 1.202 and above can click here to set up their limit caffeine reminder.

Does Caffeine Cause Sleep Problems?

Caffeine can cause sleep disturbances if you drink it too close to bedtime. But that doesn’t just mean a post-dinner coffee will keep you up. Caffeine can last in your system for 12+ hours, so even a seemingly harmless lunchtime latte can make it harder to fall asleep.

And caffeine can disrupt your sleep in two key ways: firstly by keeping or waking you up, and secondly by changing how long you spend in different sleep stages.

Caffeine can: 

  • Increase sleep latency, or how long it takes to fall asleep
  • Reduce total sleep time
  • Reduce sleep efficiency, how long you spend sleeping when in bed 
  • Worsen perceived sleep quality
  • Increase how often you wake up during the night 
  • Increase how long you’re awake during the night 
  • Reduce how much slow-wave sleep, or deep sleep, you get 
  • Reduce how much rapid-eye-movement (REM) sleep you get

Research shows caffeine can also increase your sleep latency if you’re more vulnerable to stress-related sleep disturbances.

As well as blocking adenosine, caffeine increases how much of the stress hormone cortisol you produce. This can lead to high cortisol levels, which can cause weight gain and trouble falling and staying asleep

Caffeine consumed from soda may even be associated with sleep-disordered breathing, such as sleep apnea

Caffeine can also shift the timing of your circadian rhythm. One study looked at participants who stayed in controlled conditions for 49 days. Before bed, they were either given a double-espresso caffeine dose, were exposed to bright or dim light, or were given a placebo. The light delayed the circadian rhythm (an expected result), but so did the caffeine, which delayed it by 40 minutes. 

Research shows caffeine can suppress melatonin — the hormone that primes your body for sleep — when consumed at night. This could result in you finding it harder to fall asleep and in circadian misalignment, which comes with a whole host of health issues

However, it may also show that caffeine could be useful for combating jet lag and shifting your circadian rhythm to adjust to a new time zone.

Many of us don’t even realize how much caffeine is disrupting our sleep as we get used to operating on a less-than-ideal amount of sleep each night. 

Is it Okay to Drink Caffeine Before Bed?

You shouldn’t drink caffeine before bed. Caffeine can block the sleepiness effects of adenosine, suppress melatonin, and push back your circadian rhythm — a recipe for a troubled night of sleep.

Caffeine can also increase how often you wake up during the night and reduce how much deep sleep you get — so even if you manage to get enough sleep when consuming caffeine, it can make the sleep you get not as healthy and restorative as it could be. 

Caffeine before bed, and too much caffeine in general, may even affect your heart health. One study gave participants with insomnia 400 mg of caffeine 30 minutes before bed and found it increased their heart rate and sympathetic activity and decreased parasympathetic activity. 

The researchers concluded: “These findings suggest that excessive caffeine intake may result in adverse cardiovascular events in vulnerable subjects.”  

To stop all this from happening, avoid caffeine before bed and, as caffeine can last in your system for 12 hours, cut yourself off from it earlier in the day. Check RISE for your individual caffeine cutoff time.

How to Get Caffeine Out of Your System?

We’ve all been there. You’ve had a coffee — or three — to get you through a busy morning and now you’ve got the jitters at your desk. Unfortunately, once caffeine is in your system, it’s hard to make it wear off faster. 

You can reduce its side effects by: 

  • Drinking water 
  • Getting some exercise 
  • Meditating or taking some deep breaths
  • Waiting it out — and vowing to not make the same mistake next time 

If you find yourself lying awake in bed from drinking coffee too late in the day, try: 

  • Getting out of bed and doing a relaxing activity like yoga or reading — keep the lights low to avoid waking yourself up further. 
  • Make your bedroom dark, cool, and quiet, so nothing in your sleep environment stops you from falling asleep. 
  • Meditating or doing some relaxation or progressive muscle relaxation exercises. RISE can guide you through these in the app.

We’ve covered more ways you can do to make yourself tired here. 

Why Doesn’t Caffeine Give Me Energy?

RISE app screenshot showing how much sleep debt you have
The RISE app works out how much sleep debt you have.

Ever find yourself drinking back-to-back espressos and still feeling tired? There are a few culprits for why caffeine might not be affecting you. 

These include: 

  • You’ve got high sleep debt: Sleep debt is how much sleep you owe your body compared to your sleep need, the genetically determined amount of sleep you need. Coffee can’t make up for a severe lack of sleep. Check RISE for how much sleep debt you have and what your sleep need is.
  • You’re in a dip in your circadian rhythm: Your energy levels naturally rise and fall throughout the day as part of your circadian rhythm. You may be feeling tired because you’re in a energy dip, which usually happens sometime in the afternoon. Check RISE for when these peaks and dips will be each day. 
  • You’ve built up a caffeine tolerance: The more coffee you drink, the more you need to get the same energy-boosting effects. So, if you usually only need one coffee to get you going in the morning, you might start finding it doesn’t affect you as much anymore.
  • It’s your genetics: Your genetics determine how “sticky” your adenosine receptors are, or how well caffeine can bind to them and block the fatigue-causing compound. So, some people are simply less sensitive to caffeine.

You can find out more reasons why caffeine doesn’t affect you here. 

RISE users on iOS 1.202 and above can click here to view their sleep need.

RISE users on iOS 1.202 and above can click here to view their sleep debt.

Why Does Caffeine Make Me Tired?

What’s worse than caffeine not affecting you? Caffeine making you feel more tired than before. There are a few reasons this happens. 

  • You feel the effects of adenosine again: When caffeine wears off, the tiredness you felt before and the tiredness that’s been building up can suddenly hit you at once. 
  • You’ve got high sleep debt: Caffeine can act as a pick-me-up, but it can’t mask extreme sleep deprivation. And consuming caffeine too close to bedtime can disrupt your sleep, meaning you build up sleep debt and get the urge to reach for even more coffee each day — creating a vicious circle. 
  • You’re in a dip in your circadian rhythm: If it’s the afternoon, you might be feeling the natural afternoon slump that comes with your circadian rhythm. It’s not your lunchtime coffee that’s causing it. 
  • You’re experiencing a sugar crash: If you take your coffee with sugar or flavored syrups, or turn to surgery energy drinks for caffeine, you may be experiencing a sugar crash, making you feel tired and irritable.

You can learn more about why caffeine makes you feel tired here. 

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How Long Does Caffeine Withdrawal Last?

Feeling tired, headachy, and irritable? You might be going through caffeine withdrawal. 

Caffeine withdrawal can last from two to nine days, and caffeine headaches may last for 21 days. 

The symptoms can start 12 to 24 hours after your last cup of coffee, although for some they start the same day if they miss their usual morning cup. Symptoms will be at their worst 20 to 51 hours after your last sip. 

Caffeine withdrawal symptoms include: 

  • Headaches 
  • Fatigue 
  • Depressed mood 
  • Difficulty concentrating
  • Brain fog 
  • Irritability 
  • Tremors 

Research shows these symptoms will be worse if you’re used to consuming larger amounts of caffeine and consuming it every day

You don’t need to cut out caffeine altogether to feel withdrawal, even cutting down by 100 milligrams a day can cause symptoms, which is equivalent to about one 8-ounce cup of coffee. And research suggests if you consume caffeine throughout the day, you may even feel early signs of withdrawal symptoms overnight.  

To reduce the likelihood of caffeine withdrawal, avoid going cold turkey and instead slowly cut down the amount of caffeine you have each day. 

You can learn more about how long caffeine withdrawal lasts here.

How to Stop Coffee Keeping Me Up?

You don’t need to give up coffee altogether to get a good night’s sleep. Here’s how you can enjoy a cup of joe and a restful night’s sleep. 

  • Honor your caffeine cutoff time: Use RISE to find the time of day you should be having your last coffee. Then limit, or completely avoid, caffeine after this time to give your body enough time to get all the caffeine out of your system before bed. 
  • Look out for hidden caffeine: It could be more than just coffee keeping you up. Look out for caffeinated foods and drinks including black tea, green tea, soft drinks, energy drinks, yerba mate, kola nuts, and chocolate. Avoid or limit these foods and drinks after your cutoff time. 
  • Limit your total caffeine consumption each day: You might be honoring your caffeine cutoff time, but if you’re chugging coffee up until this point, you may still have trouble sleeping. Keep your overall caffeine consumption to about 400 milligrams each day. Those who are more sensitive may want to limit themselves to less. 
  • Watch out for other sleep disruptors: Beyond caffeine-induced sleep problems, you might be kept up or woken up by large meals, bright light, late-night exercise, and alcohol too close to bedtime. Check RISE for the best time to start avoiding these things each day to get a good night’s sleep. 

Avoiding caffeine and other common sleep disruptors is part of something called sleep hygiene. Sleep hygiene is the name for the set of behaviors you can do each day to help you fall asleep faster and wake up less often throughout the night. 

The RISE app guides you through 20+ sleep hygiene habits each day and tells you the best time to do them to make them more effective. 

You can learn more about sleep hygiene here.

RISE users on iOS 1.202 and above can click here to set up their 20+ in-app habit notifications. 

How to Get Energy Without Caffeine?

Whether you’re giving up coffee altogether or simply cutting down on afternoon cups of joe, you may be wondering how on earth to get energy without caffeine. Luckily, there are science-backed ways to boost your energy, and these methods won’t disturb your sleep like caffeine can. 

Here’s what to do: 

  • Lower your sleep debt: Catch up on sleep by taking well-timed naps, going to bed a little earlier, or sleeping in a little later. Check RISE for the best time to nap to stop sleeping during the day keeping you up at night.
  • Get in sync with your circadian rhythm: Check RISE for when your body naturally wants to wake up, wind down for bed, and go to sleep. Honor these times and keep a consistent sleep schedule each day to maximize your energy levels. 
  • Reset your caffeine tolerance: If you just want to cut down on coffee, work to reset your tolerance so you don’t need to drink so much of it to get the buzz you’re looking for. Do this by slowly cutting down on caffeine and letting your body get used to consuming smaller amounts of it each day. 
  • Try caffeine-free energy boosts: Wake yourself up by taking a nap, drinking some water, or getting outside for some fresh air, exercise, and sunlight. 

Learn more about how to get more energy here. 

Should I Take a Coffee Nap?

RISE app screenshot showing best time for an energy boost
The RISE app can find the best time in your schedule for an energy boost.

A coffee nap — sometimes called a caffeine nap or a nappuccino — is when you drink a coffee and then take a short power nap. By the time you wake up, the caffeine should be kicking in, giving you a potent energy boost. 

Coffee naps can boost alertness during the day and research shows they can improve sustained attention and fatigue at night for night shift workers.

However, be careful when you take a coffee nap. If you feel yourself flagging during the afternoon slump, drinking a coffee at this time may keep you up later that night. 

Consider taking a nap without the coffee, or turning to other caffeine-free energy boosts like exercise or cold showers. 

Keep coffee naps to earlier in the day or for when it’s critical you stay awake, like before a long drive.

Learn more ways to wake yourself up here. RISE can help you find the best time in your schedule to do energy-boosting activities like taking a nap, going for a walk, and getting some natural light exposure. 

RISE users on iOS 1.202 and above can click here to connect their calendar.

Get the Sleep You Need, With or Without Caffeine

Caffeine can be useful when you need a morning pick-me-up, but it can also easily cause sleep disruption. This leads to daytime sleepiness and impaired daytime function, and a vicious circle that sees you drinking more coffee and getting less sleep. 

You don’t even need high doses of caffeine or to consume it just before bed to see these adverse effects. It can last in your system for 12 hours. 

You don’t need to give up caffeine altogether to stop it from keeping you awake, though. Use the RISE app to find out your individual caffeine cutoff time and avoid coffee, tea, and anything else with caffeine after this time. 

To boost your energy levels without turning to caffeine, keep your sleep debt low and stay in sync with your circadian rhythm. RISE can help you with both, by calculating how much sleep debt you have, and keeping track of it as you pay it back, and predicting your circadian rhythm each day, so you can sync up to it.


How does caffeine affect sleep?

Caffeine can increase the time it takes to fall asleep, increase how often you wake up during the night, reduce how much deep sleep you get, reduce total sleep time, and push back your body clock, making it harder to fall asleep at your desired bedtime.

How does caffeine keep you awake?

Caffeine keeps you awake as it binds to adenosine receptors in your brain. This means adenosine, a natural compound that helps to regulate your sleep-wake cycle, can’t bind to receptors and make you feel sleepy.

How long does the caffeine effect last?

Caffeine can last in your system for 12 hours, but this all depends on your age, metabolism, genetics, whether you regularly consume caffeine, and how much of it you’ve had that day.

How long after caffeine can you sleep?

Caffeine can last in your system for 12 hours, but some people will be able to consume it closer to bedtime and still sleep. This depends on things like your metabolism, genetics, how sensitive to caffeine you are, and how much caffeine you’ve had.

Drinking coffee before bed side effects

The side effects of drinking coffee before bed include taking longer to fall asleep, increased awakenings throughout the night, getting less deep sleep, and getting less sleep overall.

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