Caffeine studies, tips and resources
Every tip and study on this site, each in one line you can pass on. Tap Copy and it goes in a message with its link.
Tips to pass on
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If you can, get your energy from sleep, daylight soon after you wake up and a short walk first. Caffeine hides tiredness, and only sleep clears it.
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Three to four cups of coffee a day went with a 17% lower risk of dying in a 2017 review of 201 meta-analyses.
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People who drank two or more cups of tea a day had a 9 to 13% lower risk of dying over 11 years in the UK Biobank.
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Black or barely sweetened coffee went with a 14% lower risk of death in a 2025 US study. Coffee with a lot of sugar and fat showed no such link.
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Drink a lot of coffee? Use a paper filter. French press and boiled coffee let through cafestol, which raises LDL cholesterol.
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Go by the size of the cup. Have the big ones in the morning and keep anything after lunch to one small cup.
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About half of every cup is still in you 5 hours later. An 8 oz coffee at 3pm leaves about 35 mg at 11pm.
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A single espresso at 9pm leaves about 53 mg in you at 11pm, more than a can of Coke starts with.
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In a 2025 trial, 400 mg taken 12 hours before bed still cut about 21 minutes of deep sleep. 100 mg changed nothing measurable, even 4 hours before.
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For most adults, 400 mg a day isn't generally linked to negative effects, the FDA says. In pregnancy the US line is under 200, and for teens at most 100.
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A caffeine pill is usually 200 mg, about two 8 oz cups of coffee, and a strong pouch can hold as much.
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Never keep pure caffeine powder at home. The FDA says one teaspoon can hold as much caffeine as 28 cups of coffee.
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To cut down without the headache, take off about a quarter every 3 days, the latest cup first.
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In the UK Biobank, coffee went with lower death rates whatever people's caffeine genes said.
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Two weeks of your own nights, one as you are and one with the last cup earlier or smaller, tell you more than any average.
The studies
Coffee, tea and a long life
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2017. Coffee went with benefit far more often than harm, and three to four cups a day with a 17% lower risk of dying from any cause.
Poole and others, BMJ, 201 meta-analyses
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2012. Coffee drinkers first looked more likely to die, until the researchers adjusted for smoking. Then more coffee went with a lower risk.
Freedman and others, New England Journal of Medicine, 402,260 Americans
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2018. Coffee, decaf and instant included, went with lower death rates over 10 years, whatever people's caffeine genes said.
Loftfield and others, JAMA Internal Medicine, 498,134 people in the UK Biobank
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2014. Each daily cup of coffee went with 9% lower risk of type 2 diabetes, and each cup of decaf with 6%.
Ding and others, Diabetes Care, a dose-response meta-analysis
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2022. Two or more cups of tea a day went with a 9 to 13% lower risk of dying over about 11 years.
Inoue-Choi and others, Annals of Internal Medicine, the UK Biobank
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2025. Black coffee and barely sweetened coffee went with a 14% lower risk of death. Coffee with a lot of added sugar and fat didn't.
Zhou and others, Journal of Nutrition, about 46,000 US adults
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2016. Coffee moved to "not classifiable" as a cause of cancer. Drinks hotter than 65°C (149°F) probably cause cancer of the esophagus.
The World Health Organization's cancer agency, 23 scientists
The brew and your cholesterol
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1995. Paper-filtered coffee held almost no cafestol, the oil that raises cholesterol, while boiled, Turkish and French press coffee held the most.
Urgert and others, Journal of Agricultural and Food Chemistry
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2001. Unfiltered coffee raised total and LDL cholesterol, and filtered coffee barely did.
Jee and others, American Journal of Epidemiology, 14 trials
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2020. Over 20 years, filtered coffee went with a lower risk of dying than no coffee, and unfiltered coffee with a smaller benefit or none.
Tverdal and others, European Journal of Preventive Cardiology, 508,747 Norwegians
Caffeine and your sleep
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2023. Caffeine took 45 minutes off total sleep and 11 off deep sleep, but added only 9 minutes to falling asleep.
Gardiner and others, Sleep Medicine Reviews, 24 studies
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2025. 100 mg did nothing measurable at 12, 8 or 4 hours before bed. 400 mg taken 12 hours before still cut about 21 minutes of deep sleep.
Gardiner and others, Sleep, 23 young men
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2013. 400 mg at bedtime, 3 hours before or 6 hours before each cut more than an hour of measured sleep.
Drake and others, Journal of Clinical Sleep Medicine, 12 good sleepers
Energy, focus and training
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2016. From about 40 to 300 mg, caffeine improved alertness, attention and reaction time.
McLellan, Caldwell and Lieberman, Neuroscience and Biobehavioral Reviews
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2020. Caffeine improved endurance, strength, power, jumping and speed, with the biggest effect on endurance.
Grgic and others, British Journal of Sports Medicine, 21 meta-analyses
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2023. On days they were told to drink coffee, people walked 1,058 more steps and slept 36 minutes less.
Marcus and others, New England Journal of Medicine, 100 adults
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2017. Ten minutes of easy stair walking made them feel more energetic than a 50 mg caffeine capsule.
Randolph and O'Connor, Physiology and Behavior, 18 short-sleeping college women
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2008. Six weeks of easy 20-minute workouts three times a week cut fatigue by 65% and raised energy by about 20%.
Puetz, Flowers and O'Connor, Psychotherapy and Psychosomatics, 36 tired adults
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2006. A 10-minute afternoon nap improved alertness and performance at once, and some of it lasted more than 2 hours.
Brooks and Lack, Sleep, 24 young adults after a short night
How long it lasts in you
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1985. Women on low-dose estrogen pills took 7.9 hours to clear half a dose, against 5.4 hours in women who weren't.
Abernethy and Todd, European Journal of Clinical Pharmacology, 9 against 9 women
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1982. The half-life went from about 3 hours in women who weren't pregnant to 10.5 hours in the last month of pregnancy.
Knutti, Rothweiler and Schlatter, Archives of Toxicology
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2004. When they stopped smoking, caffeine clearance fell by about a third within days.
Faber and Fuhr, Clinical Pharmacology and Therapeutics, 12 heavy smokers
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1996. The antidepressant fluvoxamine took caffeine's half-life from about 5 hours to 31.
Jeppesen and others, Pharmacogenetics, 8 people
Quitting, pills and pouches
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2004. Withdrawal starts 12 to 24 hours after the last dose, is worst at 20 to 51 hours and lasts 2 to 9 days. About half get a headache.
Juliano and Griffiths, Psychopharmacology, 57 experiments and 9 surveys
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2017. Caffeine from a chewing gum peaked about 40 minutes after, the same as from a cup of instant coffee.
Sadek and others, Journal of Caffeine Research, 16 adults
History
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2023. Once tea got cheap in the late 1780s, deaths fell most in places with the worst water, since tea means boiling it.
Antman, Review of Economics and Statistics, more than 400 English parishes
Resources
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Spilling the Beans: How Much Caffeine Is Too Much? The 400 mg a day figure for healthy adults, and the warning about pure powder.
US Food and Drug Administration
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Pure and Highly Concentrated Caffeine Why one teaspoon of powder is dangerous, updated March 2023.
US Food and Drug Administration
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Caffeine Single doses up to 200 mg and 400 mg a day raise no concern for healthy adults, and 200 a day in pregnancy.
European Food Safety Authority
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Caffeine and Children At most 100 mg a day for ages 12 to 18 and no energy drinks, April 2026.
American Academy of Child and Adolescent Psychiatry
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The Effects of Caffeine on Kids: A Parent's Guide Energy drinks, caffeine pouches and the signs a child needs help, August 2025.
American Academy of Pediatrics, HealthyChildren.org
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Maternal Diet About 300 mg a day or less counts as low to moderate while breastfeeding.
US Centers for Disease Control and Prevention
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Poison Help, 1-800-222-1222 Call if someone swallowed caffeine powder or pills, and 911 for a seizure or trouble breathing.
US poison centers
