In brief
A chemical that stimulates the brain and nervous system, found in coffee, tea, cocoa, guarana, chocolate, cola and energy drinks. Moderate amounts are safe for most healthy adults.
- healthdirect's sleep advice suggests avoiding caffeine for 3 to 7 hours before bed.
- Children under 18 should have less than 2.5 mg of caffeine a day for each kilogram of body weight.
- Caffeine is one cause of heart palpitations.
How it works
healthdirect says healthy adults can safely have around 400 mg of caffeine a day, and people who are pregnant or breastfeeding should limit it to 200 mg a day. Even 100 to 200 mg can cause faster breathing and heart rate, too much can cause anxiety, and regular heavy use of more than 600 mg a day can cause insomnia.
Caffeine counteracts sleepiness by blocking the actions of adenosine. If you stop suddenly, withdrawal symptoms such as headaches, tiredness, irritability and difficulty concentrating usually start within a day and can last up to a week.
Food sources
From the AskBioMap food guide:
Connections
6 connections on the map. Select a topic to read its page.
Caffeine can cause
Too much caffeine can cause anxiety, according to healthdirect.
Sources: healthdirect Australia, Caffeine; healthdirect Australia, Anxiety
Even 100 to 200 mg of caffeine can cause a faster heart rate, and caffeine is one cause of palpitations.
Sources: healthdirect Australia, Caffeine; healthdirect Australia, Heart palpitations
Large amounts of caffeine can trigger headaches, and headaches are also a symptom of caffeine withdrawal.
Sources: healthdirect Australia, Headaches; healthdirect Australia, Caffeine
Caffeine can worsen
Regular heavy caffeine use, more than 600 mg a day, can cause insomnia, and caffeine is among the substances that make insomnia worse.
Sources: healthdirect Australia, Caffeine; healthdirect Australia, Insomnia
- Heartburn and reflux (GORD) Supported
Coffee is one of the food and drink triggers for heartburn.
Caffeine can lower
Tea and coffee reduce iron absorption, so have them between meals.
Sources
Each connection above names its own source. See every source AskBioMap uses.
Summarised from healthdirect and the NIH. Sources read on 13 and 16 October 2026. General education only, not medical advice. Spotted a mistake? Please tell us through the HuBu-Intel contact page.