The Caffeine Guide
Coffee and tea are good for most people, and the caffeine in them makes you sharper. The risks are in the sugar, in unfiltered brews and in the cup that's still in you at bedtime, since about half of it is there 5 hours later. Have the big ones in the morning and keep anything after lunch to one small cup.
Updated November 15, 2026. 16 guide pages, 38 questions, 10 myths, from 154 published sources.
Big doses in the morning.For an 11pm bedtime, a 16 oz coffee or a CELSIUS by about 11am, a full pre-workout scoop by about 9am.
After lunch, one small cup.An 8 oz coffee by about 4pm, a single espresso or a tea by about 7pm.
Then check it on your own nights.Two weeks, because people clear caffeine at very different speeds.
When should I stop drinking coffee?
When you fall asleep at 11:00pm
83 mgA measured cost
You'll fall asleep with about a cup of coffee in you.
- Brewed coffee, 8 oz95 mg
Brewed coffee, 16 oz190 mg
Your last drink, a 16 oz coffee at 3:00pm
- Under 40 mg at sleep
- by 8:10am
- Under 80 mg
- by 2:45pm
The full clock, with the band, 3am and the table by drink.
The questions people ask
Your drink
Are caffeine pills bad for you?Not at a normal dose. A pill is usually 200 mg, about two 8 oz coffees. But the health results in the studies come from coffee and tea, and pills are easy to stack.- Are caffeine pouches safe?For a healthy adult using one at a time, mostly. They hold 3 to 200 mg, so a strong one is two coffees. Nobody checks the label first, and they're not for teens.
- Does decaf have caffeine?Yes, a little. An 8 oz cup has 2 to 15 mg, a tenth of a regular coffee or less, so decaf after dinner is fine for almost everyone.
How much caffeine is in a CELSIUS?200 mg in a 12 oz can, about two cups of coffee. One at 4pm still leaves about 84 mg at an 11pm bedtime.
How much caffeine is in a Coke?34 mg in a 12 oz can of Coke and 46 mg in Diet Coke, a third to half of an 8 oz coffee. One can in the afternoon is a small dose.- How much caffeine is in a cup of coffee?About 95 mg in an 8 oz cup of brewed coffee. A 16 oz coffee-shop cup averaged 188 mg, about twice that, so the size of your cup sets the dose.
- How much caffeine is in a Monster?160 mg in a 16 oz can, more than a 16 oz Red Bull. One at 4pm still leaves about 67 mg at an 11pm bedtime.
How long it lasts
- How long does caffeine stay in your system?Half is gone in about 5 hours and a quarter is left after 10. A 200 mg drink at 2pm still leaves about 64 mg at 11pm.
How long does caffeine take to kick in?Almost all of it is absorbed within 45 minutes, and it peaks in your blood 15 minutes to 2 hours after you drink it.- What is caffeine's half-life?About 5 hours on average, anywhere from 1.5 to 9.5 in healthy adults. The pill, pregnancy and smoking move it the most.
Sleep and timing
Can I drink tea at night?Yes, if it's small or herbal. A black tea at 8pm leaves about 34 mg at 11pm, a green tea about 21 mg. Chamomile on its own has no caffeine at all.
Can I have an espresso after dinner?A single shot at 9pm leaves about 53 mg in you at 11pm, between our two lines. Have it by 7pm for a low night, or order a decaf espresso, which leaves about 13 mg.
Does caffeine affect deep sleep?Yes. Across 24 studies caffeine cut about 11 minutes of deep sleep, and 400 mg 4 hours before bed cut about 30.- Is caffeine 6 hours before bed bad?For a big dose, yes. 400 mg 6 hours before bed cut over an hour of measured sleep. A small coffee 4 hours out did nothing measurable.
Is coffee at 3pm too late?Not if it's one 8 oz cup. At an 11pm bedtime about 35 mg is left, like a can of Coke. A 16 oz cup leaves twice that.- When should I stop drinking coffee before bed?It depends on the cup more than the clock. Stop an 8 oz coffee about 7 hours before bed, a 16 oz about 12, and an espresso or tea about 4.
Does caffeine lower HRV?Answered on hrv.guide
How much
- Can you overdose on caffeine?From drinks it's very hard. Pure caffeine powder is the danger, since less than half a teaspoon is about 1,200 mg, enough to cause seizures.
- How much caffeine can a teenager have?At most 100 mg a day for ages 12 to 18, about one 8 oz coffee, and no energy drinks. Under 12, pediatricians advise against regular caffeine.
- How much caffeine can you have while breastfeeding?Up to about 300 mg a day counts as low to moderate, roughly two to three cups of coffee, by the CDC's guidance. Have it in the morning.
- How much caffeine can you have while pregnant?Under 200 mg a day, by ACOG's guidance. Late in pregnancy caffeine also clears about three times slower, so a morning cup lasts into the night.
- How much caffeine is too much?The FDA says 400 mg a day isn't generally linked to negative effects in healthy adults, about two to three 12 oz coffees.
- Is 200 mg of caffeine a lot?It's about two 8 oz coffees, half the FDA's 400 mg figure, and the whole day's line in pregnancy. At 2pm it leaves about 64 mg at 11pm.
Your body
Am I a slow caffeine metabolizer?Maybe, but your genes tell you less than tests suggest. The pill, pregnancy and smoking change it more, and a 2025 trial found no gene effect on sleep.- Does birth control make caffeine last longer?Yes. Women on low-dose estrogen pills took 7.9 hours to clear half a dose, against 5.4 hours in women who weren't.
- Does caffeine interact with antidepressants?Most medicines don't change how fast you clear caffeine. Fluvoxamine does. In 8 people it took caffeine's half-life from 5 hours to 31.
- Does coffee raise your blood pressure?For a few hours. 200 to 300 mg raised it about 8/6 mmHg in people with high blood pressure. As a daily habit, coffee raised it only about 1 point in trials.
- Is it bad to drink coffee on an empty stomach?Not for most people. In 8,013 adults and a review of 15 studies, coffee wasn't linked to ulcers or reflux. If it gives you heartburn, have it with food.
- Why does coffee hit harder after quitting smoking?Smoking speeds up the liver enzyme that clears caffeine. Within about a week of quitting, the same coffee lasts about 1.5 times as long.
Does caffeine help you burn more calories?Answered on tdee.guide
Cutting down
- How do I quit caffeine without a headache?Step down instead of stopping. Cut about a quarter every 3 days, latest drink first. From 400 mg that's under 100 in about two weeks.
- How long does caffeine withdrawal last?It usually starts 12 to 24 hours after your last dose, peaks at 20 to 51 hours and ends in 2 to 9 days. About half get a headache.
Myth or fact?
Quick calculators
The cutoff clock
Your drinks and bedtime in: what's still in you when you fall asleep, and the latest time for your last cup.
Caffeine in your drink
Guess first, then see the milligrams to scale against a cup of coffee, with the source for each.
How much is too much?
Today's drinks against the line for adults, pregnancy or teens, in cups.
Your half-life
The pill, pregnancy or smoking in: how much longer caffeine lasts in you, and how far your cutoff moves.
The step-down planner
Your milligrams a day in: a dated plan that cuts a quarter every 3 days, with the headache window.
The pre-workout window
Your weight, session and bedtime in: the dose for your weight and the latest start for a full scoop.
The guide
Everything you need to know
Is caffeine healthy?
Yes, for most adults. Coffee and tea drinkers live as long or longer in the big studies. The risks are the sugar, unfiltered brews and a big or late dose.
More energy without caffeineCaffeine studies, tips and resources
With Gyroscope One, you see the milligrams and the time of your last cup, found in your drinks, next to your sleep. Open Gyroscope
