Short answer: the FDA and Europe's food safety authority both put the safe ceiling for healthy adults at 400 mg of caffeine a day, with no more than about 200 mg in one sitting.1,2 But for most men the number that actually caps the day is not 400: it is bedtime. Caffeine's five-hour half-life means an afternoon dose is still working at midnight, and lost sleep costs you more than the caffeine gave. Here is the daily math, in real cups.
The official numbers
Two independent bodies did the reviewing. The FDA cites 400 mg a day as an amount not generally associated with negative effects in healthy adults.1 The European Food Safety Authority reached the same daily figure and added two useful refinements: single doses up to 200 mg (about 3 mg per kg of body weight) raise no safety concern, and doses above that can start to bite depending on your size and sensitivity.2 A 90 kg man has more headroom per dose than a 65 kg one; the 400 mg daily ceiling is the same for both.
What 400 mg looks like in real cups
| Drink | Typical caffeine | Toward the 400 mg ceiling |
|---|---|---|
| Brewed coffee, 8 oz (arabica) | ~95 mg | 4 cups |
| Robusta-based coffee, 8 oz | roughly double arabica | ~2 cups |
| Espresso, single shot | ~63 mg | 6 shots |
| Instant coffee, 8 oz | ~60 mg | 6–7 cups |
| Energy drink, standard can | 80–160 mg | 3–5 cans |
| Black tea, 8 oz | ~47 mg | 8 cups |
| Cola, 12 oz | ~34 mg | 12 cans |
Two traps hide in that table. Cold brew and large-format cafe drinks routinely double or triple the 8 oz numbers, and energy drinks stack caffeine with sugar, which brings its own crash. Robusta's higher caffeine is why one properly dosed cup can do the work of two; the numbers are in our robusta post and the mushroom coffee caffeine guide.
The math that actually matters: half-life
Caffeine's half-life is around five hours in a typical adult, longer for slow metabolisers and smokers' opposites.3 Run the numbers on a 200 mg coffee at 3 pm: about 100 mg is still circulating at 8 pm, and roughly 50 mg at 1 am. That is not abstract: in a controlled trial, 400 mg taken even six hours before bed cut measured sleep by more than an hour, and the sleepers did not notice the loss.4
So the practical ceiling is a time, not a milligram count. Work back eight hours from your bedtime and put your last caffeine there. For a 11 pm sleeper that is a 3 pm cutoff, which usually caps a working day at 200 to 300 mg all by itself; the sleep-debt spiral this prevents is the biggest of the four crashes we covered in why coffee makes you tired.
Signs you are over your personal limit
The official ceiling is a population average. Your own limit announces itself earlier, and it sounds like this: jitters or a racing heart on doses that used to feel fine, an anxious edge instead of focus, needing the first cup to feel merely normal, and sleep that technically happens but does not restore. The last two are the tolerance treadmill: regular high doses add adenosine receptors, so each cup buys back less.5 If that list reads familiar, the fix is not zero, it is lower and earlier, and our jitters guide covers the smoothing options.
When more stops helping
An umbrella review of over 200 meta-analyses found moderate coffee intake, around three to four cups a day, associated with the most favourable health outcomes, with benefits flattening rather than growing beyond that.6 Performance research points the same way: alertness and training effects show up at moderate doses and plateau. Past your dose, extra caffeine buys side effects, not output.
A working daily template
- Cup one, with or after breakfast: 100 to 200 mg. Whether an empty stomach matters for you is covered in coffee on an empty stomach.
- Optional cup two, early afternoon or pre-workout: up to 100 to 200 mg, finishing before your cutoff.
- Hard stop eight hours before bed. This rule outranks every other number on this page.4
- One lower-dose day a week keeps the tolerance treadmill from stealing your baseline.5
Timing questions beyond this, training days, night shifts, late workouts, are mapped in when to drink mushroom coffee.
Where Alphacino fits
A scoop of Alphacino is a measured robusta dose, the same every morning, with L-theanine in the cup to keep the curve smooth and no sugar to crash on. Knowing exactly what you took is half of doing the math; the other half, the adaptogens for the parts of energy caffeine cannot cover, is the reason the formula exists.
Frequently asked questions
Is 400 mg of caffeine a day too much?
For healthy adults, 400 mg a day is the ceiling both the FDA and EFSA consider safe. Many men feel and sleep better below it, especially if any caffeine lands within eight hours of bed.
How long does caffeine stay in your system?
The half-life is about five hours, so half of a 3 pm coffee is still working at 8 pm and a quarter at 1 am. Full clearance takes the better part of a day.
How much caffeine in one sitting is safe?
EFSA puts single doses up to 200 mg (about 3 mg per kg of body weight) as raising no concern for healthy adults. Larger single doses are where jitters, anxiety and heart-racing show up.
Why does caffeine affect me more than other people?
Genetics change how fast you clear it, body weight changes the dose per kilogram, and regular intake changes receptor counts. Your limit is personal; the signs of crossing it are jitters, anxiety and broken sleep.
What time should I stop drinking coffee?
Eight or more hours before bed. In a trial, caffeine taken even six hours before bedtime cut sleep by over an hour without the sleepers noticing.
This article is general information, not medical advice.
Sources
- U.S. Food and Drug Administration (2024). Spilling the beans: how much caffeine is too much? fda.gov
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2015). Scientific opinion on the safety of caffeine. EFSA Journal, 13(5), 4102. doi:10.2903/j.efsa.2015.4102
- Fredholm, B. B., et al. (1999). Actions of caffeine in the brain with special reference to factors that contribute to its widespread use. Pharmacological Reviews, 51(1), 83–133. PMID 10049999
- Drake, C., et al. (2013). Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine, 9(11), 1195–1200. doi:10.5664/jcsm.3170
- Juliano, L. M., & Griffiths, R. R. (2004). A critical review of caffeine withdrawal: empirical validation of symptoms and signs, incidence, severity, and associated features. Psychopharmacology, 176(1), 1–29. doi:10.1007/s00213-004-2000-x
- Grosso, G., et al. (2017). Coffee, caffeine, and health outcomes: an umbrella review. Annual Review of Nutrition, 37, 131–156. doi:10.1146/annurev-nutr-071816-064941
