Caffeine
Key facts
- Caffeine is a stimulant that acts on your brain and nervous system.
- It is found naturally in coffee, tea leaves, cocoa beans, guarana and chocolate.
- Caffeine is addictive and you may develop withdrawal symptoms when reducing your intake.
What is caffeine?
Caffeine is a chemical that can stimulate your brain and nervous system.
It is found in foods and drinks like:
- coffee
- tea leaves
- cocoa beans
- guarana — a South American plant with high levels of natural caffeine
- chocolate
- cola drinks
- energy drinks
Caffeine can also be found in small amounts in some prescription and over-the-counter medicines, such as some:
- pain-relief medicines
- cough medicines
- weight loss products
How much caffeine is in food and drink?
The amount of caffeine in food and drinks varies. For example, an espresso has more caffeine than instant coffee.
| Source | Caffeine |
|---|---|
| Espresso (50 millilitre (mL) cup) | 145 milligrams (mg) |
| Energy drink (250mL can) | 80 mg |
| Instant coffee (1 teaspoon) | 80 mg |
| Black tea (220mL cup) | 50 mg |
| Cola (375mL can) | 36 mg |
| Milk chocolate (50 gram (g) bar) | 10 mg |
How will caffeine affect my body?
Caffeine affects everyone differently.
The effect of caffeine depends on:
- your age, height and weight
- your general health and if you have a medical condition
- the amount you eat or drink
- genetic factors
- whether you regularly eat or drink caffeine
- whether other food or drugs (including alcohol) are taken at the same time
- your mood
The short-term effects of caffeine typically happen after about 30 minutes. They can last for up to 6 hours, depending on the individual.
Short-term effects after a small amount of caffeine (100-200mg) can be:
- feeling more alert and active
- higher body temperature
- faster breathing and heart rate
It's not always clear how your body will respond to caffeine. Much of the research in this area has been in coffee, which contains caffeine and many other ingredients.
What are the side effects or risks of consuming caffeine?
The amount of caffeine that is safe to have depends on your health and your age.
Healthy adults can safely have around 400mg of caffeine a day. This is the same as:
- 2 espressos
- 4 instant coffees
- 8 cups of black tea
Many regular coffee drinkers become dependent on caffeine. You may be dependent on caffeine if you find it hard to reduce how much you drink.
Regular heavy use of caffeine, more than 600mg a day, can cause:
- increased production of stomach acid causing heartburn
- stomach ulcers
- osteoporosis (bone loss) in post-menopausal women
- insomnia (difficulty sleeping)
- anxiety and depression
If you have a medical condition, it's a good idea to eat or drink less caffeine. For example, if you have high blood pressure, caffeine can increase your blood pressure. You can speak to your doctor for advice.
Children and young people who drink energy drinks that contain caffeine may have side effects like bed wetting and sleep problems. Children under 18 years of age should have less than 2.5mg of caffeine a day, for each kilogram (kg) of body weight. For a 40kg child, this is about 120mg a day, or 3 cans of cola (375mL). Having too much caffeine can cause anxiety. Foods with caffeine in your diet can take up space for other nutritious foods.
Older people can be more sensitive to the effects of caffeine. This is because it stays active in their bodies for longer.
Caffeine also stays active for longer in the bodies of babies and pregnant people.
If you are pregnant, caffeine can pass to your baby through the placenta. There is evidence to show that having drinks that contain caffeine during pregnancy can increase the risk of:
- miscarriage and stillbirth
- low birth weight
- delays in your baby's development during pregnancy
If you are pregnant or breastfeeding, it's a good idea to limit your intake of caffeine to 200mg per day. This is the same as:
- 1 espresso
- 2 instant coffees
- 4 cups of tea
Much of the research into the effects of caffeine has only looked at coffee. We still don't know much about the effects of other foods and drinks that contain caffeine.
What are the health benefits of consuming caffeine?
The effect of caffeine on your health is complex. It can cause some health problems, but it can also reduce your chances of having others.
Because caffeine is a stimulant, it can make you feel more alert and energetic.
There is some evidence that caffeine might lower the chance of developing:
Most of these studies have looked at caffeine from coffee only.
Mixing caffeine with alcohol and other drugs
Drinking or eating caffeine when taking other drugs can cause unpredictable effects. This can increase your chance of harm.
Caffeine and medicines
Caffeine can interact with over-the-counter and prescription medicines, such as:
- antibiotics
- oral contraceptives
- some antidepressants
- some heart medicines
Ask your pharmacist or doctor if any medicines that you take could be affected by caffeine.
Caffeine, alcohol and illicit drugs
When you drink alcohol with caffeine, the caffeine can hide some of the effects of the alcohol. This can cause you to drink more and lead to more risk-taking behaviours.
Caffeine does not affect the way your body absorbs alcohol. It will not reduce your blood alcohol concentration or help you 'sober up' after a big night.
Caffeine can also interact with other stimulants such as cocaine and methamphetamine. It can increase your chance of problems such as an abnormal health rate or heart rhythm.
How can I reduce my caffeine intake?
If you want to reduce or stop having caffeine, it's a good idea to do this over time. For example, drink one less caffeinated drink each day.
If you drink coffee, you can reduce your intake by switching to decaffeinated coffee.
If you drink tea, you can leave your teabag to brew for less time. You can also switch to herbal teas.
If you drink soft drinks that contain caffeine (such as cola drinks), switch to options without caffeine. You can also drink water instead.
If you want to reduce your caffeine intake, check food and drink ingredient lists for caffeine.
Caffeine withdrawal syndrome
If you stop regularly having caffeine, you may develop withdrawal syndrome. Symptoms usually start within a day of stopping caffeine. These symptoms can last up to a week. They include:
- headaches
- tiredness
- irritability
- nausea
- depression and anxiety
- sweating
- difficulty concentrating
If you drink a very large amount of caffeine regularly, withdrawal symptoms may last for more than a week.
Resources and support
You can find out more about caffeine through the Alcohol and Drug Foundation — call their Drug Info and Advice Line on 1300 85 85 84.
You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available to speak with you 24 hours a day, 7 days a week.
Learn more here about the development and quality assurance of healthdirect content.
Last reviewed: August 2025
