Caffeine affects sleep mainly by blocking adenosine, a brain chemical that builds up while you are awake and makes you feel sleepy. Because caffeine stays in the body for hours, a cup in the afternoon can still shorten and lighten your sleep at night. In a controlled study, 400 mg of caffeine taken six hours before bed cut measured sleep by more than an hour, even though people did not notice much difference themselves.
Key Takeaways
- Caffeine blocks adenosine receptors, which holds off the sleepiness that normally builds through the day.
- In an average adult, caffeine's half-life is about five hours, and it varies widely between people.
- In a 2013 study, 400 mg of caffeine taken 0, 3 or 6 hours before bed each reduced measured sleep time, by about 1.1 to 1.2 hours.
- A 2023 analysis of 24 studies found caffeine reduced total sleep by 45 minutes on average and reduced deep sleep.
- The FDA cites 400 mg a day, about two to three 12-ounce cups of coffee, as an amount not generally linked to negative effects in most adults.
- Timing matters as much as amount: the same 2023 analysis suggested a cup of coffee at least 8.8 hours before bed to protect total sleep time.
Evidence grade: Strong. Caffeine's effects on sleep are supported by randomized controlled trials summarized in two systematic reviews, including a 2023 meta-analysis of 24 studies, plus an established FDA reference amount for daily intake.
How Caffeine Affects the Brain
Caffeine is the most widely consumed psychoactive substance in the world [4]. It is found naturally in more than 60 plants, including coffee beans, tea leaves, kola nuts and cacao, and synthetic caffeine is added to some medicines, foods and drinks such as energy drinks [2].
The main reason it keeps you awake involves adenosine. Adenosine is widely accepted as a natural sleep-regulating substance in the brain, and caffeine acts as an antagonist at the receptors adenosine normally binds to, which reduces sleepiness [5]. Put simply, the longer you are awake, the more sleep pressure builds; caffeine blocks the signal rather than removing the need for sleep. When it wears off, the sleep pressure is still there.
Caffeine use is common. In a nationally representative U.S. beverage survey of 37,602 people aged 2 and older, 85% consumed at least one caffeinated beverage a day. Average intake from beverages was 165 mg a day, and coffee was the main source in every age group [7].
Caffeine Half-Life: How Long It Stays in Your System
Caffeine reaches its peak level in the blood within about an hour, and you may keep feeling its effects for four to six hours [2]. Its half-life, the time it takes the body to clear half of a dose, is about five hours in an average-sized adult or child over age 9, according to the National Library of Medicine's PubChem database. That figure can change a lot [8]:
- Smoking can shorten caffeine's half-life by up to 50%.
- Pregnancy lengthens it, to 15 hours or more late in pregnancy.
- Newborns clear caffeine far more slowly than adults.
Genes matter too. Most caffeine is broken down by a liver enzyme called CYP1A2, and common genetic differences in that enzyme and in the adenosine A2A receptor help explain why some people sleep fine after an evening espresso while others are wired for hours [9]. Researchers also note that the sleep of older adults may be more sensitive to caffeine than that of younger adults [4].
| Drink | Typical caffeine | Roughly left at bedtime if taken 6 hours earlier* |
|---|---|---|
| 8-ounce cup of coffee | 95-200 mg | About 45-90 mg |
| 8-ounce energy drink | 70-100 mg | About 30-45 mg |
| 8-ounce cup of tea | 14-60 mg | About 6-25 mg |
| 12-ounce can of cola | 35-45 mg | About 15-20 mg |
Caffeine amounts from MedlinePlus [2]. *Rough estimate assuming a five-hour half-life [8]; your own rate may be faster or much slower.
What the Research Shows About Caffeine and Sleep Patterns
The 2013 six-hour study
The study most often cited on caffeine timing was published in 2013 in the Journal of Clinical Sleep Medicine. Researchers gave 12 healthy normal sleepers 400 mg of caffeine or a placebo at bedtime, 3 hours before bedtime, or 6 hours before bedtime, and tracked their sleep at home with a sleep monitor and a sleep diary [3].
- All three caffeine timings significantly reduced total sleep time on the monitor compared with placebo, by about 1.1 to 1.2 hours.
- Even at six hours before bed, caffeine reduced sleep by more than an hour.
- Caffeine also increased time awake during the night and lowered sleep efficiency.
- At six hours, the sleep diaries showed a smaller, non-significant loss of 41 minutes: people underestimated how much sleep they had lost.
The authors concluded that the results support the common advice to avoid substantial caffeine for at least six hours before bed [3]. Keep in mind that 400 mg is a large single dose, about the FDA's full-day reference amount, and the study was small.
Systematic reviews
A 2017 systematic review of epidemiological studies and randomized trials found that caffeine typically took longer to fall asleep, reduced total sleep time and sleep efficiency, and worsened perceived sleep quality. It also reduced slow-wave (deep) sleep and increased light stage-1 sleep, wakefulness and arousals, with clear dose and timing effects [4].
A 2023 meta-analysis of 24 studies put numbers on these effects. On average, caffeine [6]:
- reduced total sleep time by 45 minutes
- reduced sleep efficiency by 7%
- added 9 minutes to the time it took to fall asleep
- added 12 minutes of time awake after first falling asleep
- increased light sleep and cut deep sleep by about 11 minutes
The authors estimated that, to avoid losing total sleep time, a standard coffee (107 mg per 250 mL) should be taken at least 8.8 hours before bed, and a typical pre-workout supplement (217.5 mg) at least 13.2 hours before bed [6].
How Much Caffeine Is Too Much?
For most adults, the FDA has cited 400 mg a day, about two to three 12-fluid-ounce cups of coffee, as an amount not generally associated with negative effects. The FDA adds that people vary widely in how sensitive they are to caffeine and how fast they clear it [1]. MedlinePlus also notes that children and teens should not have as much caffeine as adults [2].
Signs that you may be having too much include a faster or pounding heartbeat, trouble sleeping, jitters, feeling anxious, an upset stomach, nausea and headache. The FDA suggests talking with your health care professional about your caffeine intake if you notice these [1].
A daily total under 400 mg does not guarantee good sleep. The research above suggests that when you have caffeine can matter as much as how much.
Tips for Managing Caffeine for Better Sleep
- Set a cut-off time. Six hours before bed is a minimum based on the 2013 study [3]; the 2023 meta-analysis suggests closer to nine hours for a regular coffee and longer for high-dose products [6].
- Count every source. Tea, cola, energy drinks, chocolate, pre-workout products and some pain relievers and cold medicines can contain caffeine [2].
- Cut back gradually. If you stop suddenly after regular use, you may get withdrawal symptoms such as headaches, drowsiness, irritability, nausea and trouble concentrating. These usually go away after a couple of days [2].
- Do not rely on how you feel. In the 2013 study, people lost more sleep than they reported [3].
- Build the rest of the routine. A consistent sleep and wake time and a dark, quiet, cool bedroom support good sleep. Food choices can help too; see our guides to nutrition for enhanced sleep quality and caffeine-free herbal teas.
- Find other afternoon lifts. A short walk, water and a balanced snack can help with the mid-afternoon slump; see snacks that boost energy without the crash.
Where an Evening Supplement Fits
No supplement cancels out late caffeine. Moving your last cup earlier is the most direct fix. Some adults also like a nighttime supplement as part of a wind-down routine. OPA Sleep Well Gummies provide 2 mg of melatonin plus a 100 mg blend of chamomile, lemon balm, valerian and lavender per two-gummy serving, which adults take before bedtime. Each serving also contains 4 g of added sugar.
Research on melatonin is mixed. The National Center for Complementary and Integrative Health (NCCIH) says melatonin may help with jet lag and some sleep-timing problems, but that there is not enough strong evidence to recommend it for long-term trouble sleeping. Short-term use appears to be safe for most people, while long-term safety information is lacking [10].
Safety and Interactions
- Who should check before using caffeine: MedlinePlus advises checking with your health care provider about limiting or avoiding caffeine if you are pregnant or breastfeeding, have sleep problems, frequent headaches, anxiety, acid reflux or ulcers, heart rhythm problems or high blood pressure, or if you are a child or teen [2].
- Medicines: caffeine can interact with stimulants, certain antibiotics, asthma medicines and heart medicines. Ask your doctor or pharmacist if you take any of these [2].
- Concentrated caffeine: the FDA warns that pure and highly concentrated caffeine products can have serious health consequences; it estimates toxic effects can occur with rapid intake of around 1,200 mg, less than half a teaspoon of pure caffeine [1].
- Melatonin: if you take medicine, consult your health care provider before using melatonin. There may be a risk of allergic reactions, its safety in pregnancy and breastfeeding has not been well studied, and it may stay active longer in older adults, which can cause daytime drowsiness [10]. OPA Sleep Well Gummies are labeled for adults.
Frequently Asked Questions
How does caffeine affect sleep?
Caffeine blocks the receptors for adenosine, a natural sleep-promoting signal in the brain. Studies show it can lengthen the time it takes to fall asleep, shorten total sleep, add wake time during the night and reduce deep sleep.
How many hours before bed should I stop drinking caffeine?
At least six hours, based on the 2013 study in which 400 mg six hours before bed still cut measured sleep by more than an hour. A 2023 meta-analysis suggested about 8.8 hours for a regular cup of coffee and about 13 hours for a high-dose pre-workout product.
What is the half-life of caffeine?
About five hours in an average adult, meaning half a dose is still in your body five hours later. It can be much shorter in people who smoke and much longer during pregnancy, and genetics also affects how fast you clear it.
Can caffeine make you feel jittery or anxious?
Yes. The FDA lists jitters, feeling anxious, a fast or pounding heartbeat, upset stomach, nausea, headache and sleep disruption among the signs of too much caffeine. Sensitivity varies a lot between people, so talk with your health care professional if you notice these effects.
Is 400 mg of caffeine a day safe?
For most healthy adults, the FDA cites 400 mg a day as an amount not generally associated with negative effects. That amount can still disturb sleep if it is taken late in the day, and some people, including those who are pregnant and children and teens, should have less.
Can caffeine withdrawal affect sleep?
Stopping suddenly after regular use can cause headaches, drowsiness, irritability, nausea and trouble concentrating, which usually pass within a couple of days. Cutting back gradually and moving caffeine earlier in the day are gentler ways to improve sleep.
Sources
- U.S. Food and Drug Administration. Spilling the Beans: How Much Caffeine Is Too Much? FDA Consumer Update.
- MedlinePlus. Caffeine. National Library of Medicine.
- Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. J Clin Sleep Med. 2013.
- Clark I, Landolt HP. Coffee, caffeine, and sleep: a systematic review of epidemiological studies and randomized controlled trials. Sleep Med Rev. 2017.
- Reichert CF, Deboer T, Landolt HP. Adenosine, caffeine, and sleep-wake regulation: state of the science and perspectives. J Sleep Res. 2022.
- Gardiner C, Weakley J, Burke LM, et al. The effect of caffeine on subsequent sleep: a systematic review and meta-analysis. Sleep Med Rev. 2023.
- Mitchell DC, Knight CA, Hockenberry J, Teplansky R, Hartman TJ. Beverage caffeine intakes in the U.S. Food Chem Toxicol. 2014.
- PubChem. Caffeine (CID 2519): Biological Half-Life. National Library of Medicine.
- Nehlig A. Interindividual differences in caffeine metabolism and factors driving caffeine consumption. Pharmacol Rev. 2018.
- National Center for Complementary and Integrative Health. Melatonin: What You Need To Know. NCCIH.
Disclosure: OPA Nutrition sells supplements, including products mentioned in this article. This content is for education only and is not medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your healthcare provider before using any supplement, especially if you take medication or have a medical condition.
Written and reviewed by Michael Gonzales, Founder, OPA Nutrition · Last reviewed: · How OPA researches and writes
