Caffeine can sharpen focus and improve exercise performance — but too much causes jitters, anxiety and poor sleep.
Safe limits
- Most healthy adults: up to around 400mg a day.
- Pregnancy: no more than 200mg a day.
- Children and teenagers: should limit caffeine; high-caffeine energy drinks aren't recommended.
Caffeine in common drinks (approximate)
| Drink | Caffeine |
|---|---|
| Mug of filter coffee | ~140mg |
| Mug of instant coffee | ~100mg |
| Single espresso | ~60–80mg |
| Mug of tea | ~75mg |
| 250ml energy drink | ~80mg |
| Can of cola | ~40mg |
| 50g plain chocolate | up to ~50mg |
Coffee-shop drinks vary widely; a large coffee can exceed 300mg.
Sleep
Caffeine's effects can last many hours. Many people sleep better if they stop caffeine around 8 hours before bed.
Exercise
Around 3mg per kg of body weight about an hour before exercise can improve performance in many people.
Signs you're having too much
Restlessness, anxiety, a racing heart, upset stomach, headaches and difficulty sleeping. Cut back gradually to avoid withdrawal headaches.