How much caffeine is too much?

For many of us, the day doesn't start until we've had a coffee. Caffeine can improve alertness and even exercise performance, but too much, or at the wrong time, can backfire.

How much is safe?

For most healthy adults, up to about 400 mg of caffeine a day is generally considered safe by authorities like the US FDA. During pregnancy, the usual advice is to stay under 200 mg a day.

How much is in your drink?

Amounts vary a lot by brand and preparation, but roughly:

• Brewed coffee (240 ml cup): around 80–100 mg
• Espresso shot: around 60–75 mg
• Black tea: around 40–50 mg per cup
• Green tea: around 30–40 mg per cup
• Energy drinks: often 80 mg or more per can, sometimes much more
• Dark chocolate: a small amount, around 20 mg per 30 g

Timing matters

Caffeine's effects can last for hours: on average it takes around five hours for your body to clear half of it, longer for some people. A coffee at 4pm can still be affecting you at bedtime.

Signs you're having too much

• Jitteriness or anxiety
• A racing heart
• Trouble falling asleep
• Stomach upset
• Headaches when you skip it

Watch what comes with it

Large coffee-shop drinks with syrups, cream and sugar can contain several hundred calories. Black coffee, tea or a coffee with a splash of milk are easy swaps if you're watching your calories.

Cutting back

Reduce gradually to avoid withdrawal headaches. Swap one coffee a day for decaf or herbal tea, and make sure you're eating regular meals and sleeping enough, so you don't need caffeine to run on.