Caffeine

May improve performance in specific tasks; weigh benefits against anxiety and sleep loss.

• Tier A — Consistent support for specific uses
• Performance

What it is for

Strength and endurance performance, focus and a lower perception of effort.

How it works

An adenosine receptor antagonist: it reduces the sensation of fatigue and increases central nervous system activation.

Dosing

In healthy adults, start low. EFSA identifies up to 200 mg per dose and 400 mg/day from all sources as generally not raising safety concerns; these are not targets or individual guarantees. Sports doses of 3–6 mg/kg can exceed these reference amounts.

When to take it

30–60 min before exercise. Sleep: as a cautious starting point, allow ≥9 h before bed for about 100 mg (a coffee) and ≥13 h for about 200 mg (a pre-workout). These are population estimates, not guarantees; larger doses may require more time. Deep-sleep changes were observed with 400 mg even 12 h before bed.

Safety

Safe at moderate doses. High doses: anxiety, tachycardia, insomnia.

Side effects

Jitteriness, stomach discomfort, disrupted sleep, mild dependence.

Interactions

It adds to other stimulants; be careful with heavily loaded pre-workouts.

Contraindications

Arrhythmias, uncontrolled hypertension, anxiety, pregnancy (limit to <200 mg/day).

Who it has been studied in

Response depends on dose, sleep, habitual use and other factors. A single genotype cannot reliably predict individual benefit.

Frequently asked

What this rests on