What it is
Caffeine is a nervous system stimulant found in coffee, tea, cocoa and energy drinks, and is also sold as capsules, gels and "pre-workout" powders. It has authorised EU health claims: it helps maintain alertness and concentration (from 75 mg per serving) and improves endurance performance.
What matters most at the counter is the total: people add coffee, energy drinks and pre-workout without doing the sum. The European Food Safety Authority considers up to 200 mg at once and 400 mg a day safe in healthy adults, and 200 mg a day in pregnancy.
What it does
It blocks adenosine receptors, the molecule that signals sleepiness:
- It reduces the feeling of tiredness and improves attention for a few hours.
- It speeds the heart slightly and raises blood pressure a little, briefly.
- With daily use tolerance builds up, and stopping suddenly brings headache and fatigue.
At the counter
When to recommend it
- Healthy adult who wants more focus or a one-off performance boost
- About 3 mg per kilo an hour before endurance exercise, never above 200 mg at once
- Someone who already drinks coffee and wants to keep track of the total
When not to
- Pregnancy: 200 mg a day maximum in total, from all sources
- Minors: energy drinks are not recommended
- Arrhythmia, poorly controlled high blood pressure, anxiety or insomnia without checking with their doctor first
Warnings
- Important PREGNANCY AND BREASTFEEDING: cap of 200 mg a day adding up coffee, tea, cola, cocoa and supplements.
- Important A pre-workout may contain 200-400 mg per serving and several stimulants together: read the label and do not add it to coffee or energy drinks.
- Caution Fluvoxamine and some quinolones (ciprofloxacin) slow its elimination: the same dose acts more and lasts longer.
- Caution Palpitations, tremor, anxiety or insomnia are a reason to lower the dose or stop; with chest pain, see a doctor.
- Worth knowing Taken late in the afternoon, it worsens sleep even when you do not notice it at bedtime.
Pharmacokinetics
- Absorption
- Fast and almost complete; the peak comes at 30-60 minutes.
- Distribution
- Spreads through the whole body, crosses the placenta and passes into milk.
- Metabolism
- In the liver, mainly through the CYP1A2 enzyme.
- Elimination
- Half-life around 5 hours, much longer in pregnancy and with some drugs.
Where the caffeine comes from
| Aspect | Usual source | Pre-workout or capsules |
|---|---|---|
| Amount | Variable, 40 to 100 mg per serving | Labelled, often 150-400 mg |
| Other ingredients | Few | Usually more stimulants |
| Adds up with others | Yes, almost always unintentionally | Yes, and where people overshoot most |
| What to check | How many servings a day | The label and the daily total |
The risk is not caffeine itself, it is the total from every source added together.
Self-assessment
Three questions. When you check your answers you will see the explanation for each one.
-
EFSA gives 400 mg a day, and 200 mg in a single dose.
-
200 mg a day adding up all sources.
-
CYP1A2 inhibition prolongs and increases the effect of caffeine.
Training content. It does not replace the summary of product characteristics or clinical judgement.