Supplements3 min read

Caffeine: the dose and the bill

The most effective legal performance drug there is, with a half-life long enough to still be in you at bedtime. Here is how to use it, and what it quietly costs.

By Max van Strydonck

Founder of VERTEXPublished 21 April 2026

Caffeine is the only supplement in most people's stack that they would notice missing within a day. It is also the one they think least carefully about, because it arrives as a beverage rather than a dose.

Used deliberately it improves strength, endurance and how hard a session feels. Used carelessly it borrows performance from tomorrow.

3–6 mg/kg

The performance dose — around 240–480 mg for an 80 kg lifter

~5 h

Half-life — half of it is still circulating five hours later

What it actually does

Caffeine blocks adenosine receptors. Adenosine accumulates through the day and is part of how your brain registers fatigue, so blocking it does not create energy — it suppresses your perception of not having any.

That distinction matters, because it explains the pattern of the benefits.

Effect on training

Where caffeine helps most.

relative size of the performance benefit

Perceived exertion

how hard it feels

Large

Muscular endurance

reps at a given load

Solid

Endurance performance

time trials

Solid

Maximal strength

1RM

Small

Power output

jumps, sprints

Small–moderate

Direction and relative magnitude from the meta-analytic caffeine literature and the ISSN position stand on caffeine and exercise performance. Endurance and perceived effort respond most reliably.

The largest and most reliable effect is on how hard training feels. That is not a trivial benefit — a session that feels 10% easier is a session where you do the last two sets properly instead of cutting them.

45 min

Plasma caffeine peaks roughly 30 to 60 minutes after ingestion. Taking it as you walk into the gym means it arrives for your third exercise. Take it before you leave the house.

The dose, in real units

The research dose of 3–6 mg per kilogram sounds abstract until you convert it into things people actually drink.

What 300 mg looks like

Caffeine, in ordinary objects.

~95 mg

A standard mug of filter coffee

Highly variable — anywhere from 70 to 140 mg depending on bean, grind and brew. Coffee is the least precise delivery method there is.

Variable

~65 mg

A double espresso

Less than most people assume. Espresso is concentrated, not large.

Variable

~50 mg

A mug of black tea

Around half a coffee. Green tea is lower again, roughly 30 mg.

Low

~200 mg

A typical pre-workout scoop

Often more. This is where accidental over-dosing happens, particularly when it lands on top of a normal coffee day.

Check the label

200 mg

A caffeine tablet

The only precise option. Unglamorous, cheap, and the sensible choice if you are actually dosing rather than drinking.

Precise

Approximate values; caffeine content in brewed drinks varies widely by preparation. Regulatory guidance in most countries places 400 mg per day as a reasonable upper limit for healthy adults.

Starting at the low end is genuinely worth doing. The dose-response for performance flattens out well before the dose-response for jitteriness, anxiety and a wrecked night does.

The bill arrives at bedtime

Here is the part that gets ignored. Caffeine's half-life is around five hours, with wide individual variation — some people clear it in three, some in seven or more.

300 mg at 2pm

Where it is at bedtime.

2pm
300 mg
Pre-workout dose. Peaks around 3pm, session feels great.
7pm
150 mg
One half-life in. Still roughly a strong coffee's worth circulating, and you no longer notice it because you are habituated.
midnight
75 mg
Bedtime. A cup of tea's worth of adenosine blockade, sitting between you and deep sleep.
5am
37 mg
And you wake up tired, and the fix is a coffee. This is the loop.

Based on a ~5 hour half-life. Controlled work has shown 400 mg taken six hours before bed measurably reduces total sleep time — even in people who report no subjective effect.

The finding worth internalising is that people are bad judges of this. In controlled conditions, a dose taken six hours before bed reduced sleep meaningfully in participants who did not report feeling affected. "It doesn't keep me awake" is not evidence.

"Caffeine doesn't affect my sleep, I can drink it at 8pm."

You just can't feel it

Measured sleep disruption from late caffeine occurs in people who report no subjective effect. Habituation dulls the sensation, not the pharmacology.

Given that sleep is one of the more powerful recovery variables available to a lifter, a habit that trades an hour of it for a slightly better evening session is a bad trade made invisibly.

Tolerance, and whether to cycle

Tolerance to caffeine's alertness effects develops quickly. Tolerance to the performance effects appears to develop less completely — habitual users still get an ergogenic benefit, though probably a smaller one.

Whether to periodically abstain is genuinely unsettled. A pragmatic approach: keep your baseline daily intake modest, and reserve the larger deliberate doses for sessions where they matter. That way there is somewhere to go.

Using it well

Take it 45–60 minutes before you train, not on arrival.
Start at 3 mg/kg. Move up only if the low dose does nothing.
Set a cut-off at least eight hours before bed. For most people that means nothing after early afternoon.
Count your total. Pre-workout plus two coffees plus a green tea adds up faster than anyone tracks.
Skip it on easy days. Keeps tolerance down and gives it somewhere to work.

The short version

Caffeine is the most effective legal performance aid available, it works best on how hard training feels, and 3–6 mg/kg an hour beforehand is the dose.

Then respect the half-life. A pre-workout at 6pm is still with you at midnight, and the sleep it costs is worth more to your training than the session it improved.