Caffeine: What It Actually Does, How Much to Take, and When It Is Pointless

Caffeine is one of the very few supplements with a serious pile of research behind it, and it genuinely does what people expect it to do. The problem is that most people take it at random: too much, too late in the day, and every single day without a break. Here is what it actually does in your body, how much you need, and when you are better off skipping it.

What caffeine actually does

Caffeine does not give you energy. It has no calories and it does not create fuel for your muscles. What it does is block adenosine receptors in your brain — adenosine is the molecule that builds up across your waking day and tells you that you are tired. When caffeine occupies that spot, the tiredness signal arrives muffled.

The practical result is simple: the same workout feels easier. A set of 10 reps with 80 kg feels like 7/10 effort instead of 8.5/10. The bar is not lighter — you are just more willing to push into it. On top of that you get slightly better muscle fibre recruitment and a shorter reaction time.

The numbers from the research are moderate, not dramatic:

• maximal strength (1RM squat and bench): roughly 2-7% better
• reps to failure at the same load: usually 1-2 extra reps in sets of 8-12
• endurance (running or cycling, 20-60 minutes): 2-4% faster times
• vertical jump: 2-4 cm, with big individual variation

That is a difference you see on a six-month graph, not the session where you suddenly add 20 kg to your lifts.

Dose: count per kilogram, not per cup

The dose used in most of the research is 3-6 mg per kilogram of body weight, taken 45-60 minutes before training.

• 60 kg → 180-360 mg
• 80 kg → 240-480 mg
• 100 kg → 300-600 mg

If you have never measured what you take, start at the low end — 3 mg/kg — and do it on a normal training day, not on the day you test a max. Above 6 mg/kg there is essentially no extra benefit, while jitters, hand tremor and elevated heart rate keep climbing. The commonly accepted ceiling for healthy adults is around 400 mg per day total, from all sources combined.

How much is in what you already drink

• espresso (30 ml): 60-80 mg
• filter or stovetop coffee (200 ml): 90-150 mg
• instant coffee (200 ml): 60-80 mg
• energy drink: 80 mg in a 250 ml can, 160 mg in a 500 ml can
• black tea (200 ml): 40-60 mg; green tea: 25-40 mg
• tablet or powder: typically 100-200 mg per serving

Coffee can vary by a factor of two depending on the bean and the brew, so if precision matters to you, a measured tablet is the only version where you actually know your intake.

Timing

A tablet or a coffee peaks in your blood in 45-60 minutes. The half-life of caffeine is 4-6 hours — meaning 300 mg taken at 5 p.m. still leaves roughly 150 mg circulating at 11 p.m.

If you train in the morning, take it an hour before your first set and that is the whole story. If you train in the evening, do the math on what it costs your sleep.

The real price: your sleep

A 400 mg dose taken 6 hours before bed shortens sleep by about 1 hour and degrades its quality — including in people who insist coffee never bothers them. Less sleep means worse recovery, a weaker session tomorrow, and a bigger perceived need for caffeine. That is the loop.

The rule that works: last dose at least 8-9 hours before bed. If you go to sleep at 11 p.m., nothing after 2-3 p.m.

If you need caffeine just to get through the gym door three days in a row, the problem is not your dose — it is your sleep and your food.

Tolerance and breaks

Tolerance to the alertness effect develops in 5-20 days of daily use. The performance effect holds up better, but it still fades. Two options that work in practice:

1. Use it only on your 2-3 hardest sessions per week, and take nothing on the other days.
2. Take a 7-10 day break every 2-3 months.

Expect a headache 12-24 hours after stopping, plus fatigue and poor focus. It lasts 2-9 days. If you taper instead — cutting 50 mg every 2-3 days — you can get through it with almost no symptoms.

When it makes no sense

• You train after 6 p.m. and go to bed before midnight.
• You regularly sleep less than 6 hours — caffeine only masks that problem.
• A light technique or mobility session; there is nothing to gain.
• You get anxiety, tremor or a racing heart at as little as 100-150 mg.
• You are using it instead of a meal. It is not food and it will not fix a 500 calorie shortfall.

When to see a doctor

Caffeine is harmless for most healthy adults at the doses above, but talk to a doctor if:

• you feel skipped beats or pounding that continues an hour or two after the effect wears off;
• you have high blood pressure, a known arrhythmia, or any heart condition;
• you are pregnant or breastfeeding — the ceiling drops to around 200 mg per day, and that is a conversation for a doctor, not the internet;
• you take thyroid medication, antidepressants, certain antibiotics or heart medication — interactions are real;
• you have panic attacks, chronic insomnia, or reflux that gets worse;
• you are under 18 — the general guideline is a maximum of 2.5 mg/kg per day, and competition use is worth discussing with a doctor first.

The short version

• Caffeine does not create energy — it lowers perceived effort: about 1-2 extra reps per set and 2-7% on strength.
• The dose is 3-6 mg/kg taken 45-60 minutes before training; at 80 kg that is 240-480 mg. More than that buys only side effects.
• Cap total intake at 400 mg per day from all sources; a 200 ml filter coffee is 90-150 mg, a 500 ml energy drink is 160 mg.
• Last dose 8-9 hours before bed, or you lose an hour of sleep and everything you gained.
• Use it on your 2-3 hardest sessions per week rather than daily, and take a 7-10 day break every 2-3 months.