Caffeine is found in the leaves, seeds, and fruits of over 60 plants worldwide. Caffeine naturally occurs in tea, coffee, and chocolate. It is added to ‘cola’ type soft drinks and energy drinks.

What does caffeine do?

Caffeine has a stimulant effect on your central nervous system. This can help the brain to produce faster and clearer thoughts, take away feelings of tiredness and improve exercise performance.

Too much caffeine can cause irritability, anxiety, an increase in heart rate, and insomnia. It all depends on the rate that your body metabolises caffeine and how much caffeine you usually have (as our bodies can acquire a tolerance to the effects of caffeine). Quick metabolisers process caffeine fast, while slow metabolisers eliminate the caffeine more slowly and can feel the effects many hours afterwards.

Often you may hear that caffeine has a diuretic effect (increases the rate of urination): this is true, but in a cup of tea and coffee there is plenty of fluid to offset these losses.

How much caffeine can we have?

There are no firm recommendations on caffeine consumption- how much caffeine you can have will depend on your individual response to it. For the general population, 400mg or 3 cups of coffee each day has been determined to be safe, however, you should have less if you are more sensitive to caffeine (e.g. you get anxious or jittery) (EFSA, 2015; FSANZ, 2021).

  • Pregnant women are advised to limit the amount of caffeine they consume each day to around 2 cups of coffee (<200mg caffeine), as pregnancy slows down the rate that caffeine is metabolised (Ministry of Health, 2020). High caffeine levels have been linked to low birth weight and reduced fertility in women trying to conceive,
  • Breastfeeding women should be aware that caffeine may have a stimulating effect on their baby. It is recommended that breastfeeding women limit caffeine to no more than 6 cups of tea or 3 single-shot espressos per day.
  • Children do not need to include caffeine in their diet. Caffeine in children has been linked to irritability, sleep problems, aggressive behaviour, and attention and conduct problems.
  • Energy drinks: Caffeine is present in many more products these days, particularly energy drinks. These drinks contain more added sugar than is recommended so it is best if these drinks are avoided, particularly for children and pregnant women as we don’t know the effects of early exposure to caffeine.
  • Athletes: Studies suggest that consuming caffeine before exercise can improve physical performance. Different people need different doses, but typically doses in the range 1-3 mg caffeine per kg body weight are sufficient to improve performance in trained athletes (e.g. 70-210mg in a 70kg athlete) (Sports Dietitian Australia, n.d.). For your average gym-goer, a cup of coffee 45-60 min before exercise (perhaps along with some quick digesting carbs e.g. a slice of toast) is a great pre-workout option.

How much caffeine is in food and drinks?*


Average Caffeine Content (mg)

Coffee (cappuccino) (260ml)105
Energy drinks (250 ml can)80-120

Instant Coffee (1 cup)

Black tea (1 cup)47
Cola drinks (355ml can)35
Chocolate bar (50g)33
Green tea (1 cup)31
Decaffeinated long black coffee (130ml)19
Drinking chocolate (1 cup)5

Source: Ministry of Health, 2020 (Figure 4)

*Note these are rough estimates, the caffeine in food and drink can change with different brands, cafés and brewing times.


Caffeine has a long half-life, which means it lingers in your bloodstream for a long time. Even if you fall asleep fine,  caffeine still in your system past bedtime can disrupt the quality of your sleep. For this reason, it is recommended that you avoid consuming caffeine past the late afternoon (e.g. past 2-4 pm) (Sleep Foundation, 2022).

For more information about caffeine, click to read the attached article from Professor Elaine Rush

More info


Last reviewed 01/06/2022

Last modified: July 1, 2022