Last published: October 06, 2020

What is caffeine?

Caffeine is a stimulant drug, which means it speeds up the messages travelling between the brain and the body.

It’s found in the seeds, nuts and leaves of a number of different plants, including:

  • Coffea Arabica (used for coffee)
  • Thea sinensis (used for tea)
  • Cola acuminata (used as a nut, tea or in soft drinks including cola)
  • Theobroma cacao (used in cocoa and chocolate)
  • Paulinia cupana (used as guarana in snack bars and energy drinks).1

How is caffeine used?

Caffeine is used in a number of different products. The amount of caffeine in these products can vary dramatically, so it’s always best to check the label. The average amounts are listed below.

Average amounts

Product Average caffeine content (mg/100 ml)
Red Bull® 32.0
Mountain Dew® 15.0
Coca Cola® 9.7
Diet Coke® 9.7
Coke Zero® 9.6
Brewed black tea 22.5
Brewed green tea 12.1
Coffee, cappuccino 101.9
Coffee, flat white 86.9
Coffee, long black 74.7
Coffee, from ground coffee beans, espresso style 194.0
Chocolate, milk with added milk solids 20.0
Chocolate, dark, high cocoa solids 59.0

Adapted from Food Regulation Standing Committee, Caffeine Working Group. (2013). The regulation of caffeine in foods.

Effects of caffeine

There is no safe level of drug use. Use of any drug always carries some risk. It’s important to be careful when taking any type of drug.

Caffeine affects everyone differently, based on:

  • size, weight and health
  • whether the person is used to taking it
  • whether other drugs are taken around the same time
  • the amount taken

The following effects may be experienced between 5 to 30 minutes after consuming caffeine, and may continue for up to 12 hours:

  • feeling more alert and active
  • restlessness, excitability and dizziness
  • anxiety and irritability
  • dehydration and needing to urinate more often
  • higher body temperature
  • faster breathing and heart rate
  • headache and lack of concentration
  • stomach pains.3

Children and young people who consume energy drinks containing caffeine may also suffer from sleep problems and anxiety.4


If a large amount of caffeine is consumed it could also cause an overdose. Call an ambulance straight away by dialling triple zero (000) if you experience any of the following effects.

  • tremors
  • nausea and vomiting
  • very fast and irregular heart rate
  • confusion and panic attack
  • seizures.5

It’s possible to die from having too much caffeine, but this is extremely rare. This would usually only happen if 5–10g of caffeine (or 80 cups of strong coffee) were consumed one after the other.1

In small children, caffeine poisoning can happen if a lower amount, such as around 1g of caffeine (equal to around 12 energy drinks) is consumed one after the other.6

Coming down

Some people consume drinks with caffeine so that they can continue working or studying at night. However, the after-effect is that they will feel tired and lethargic the next day.

Long-term effects

Regular, heavy use of caffeine (such as more than 4 cups of coffee a day) may eventually cause:

  • nervousness
  • difficulty Sleeping
  • restlessness
  • irritability and headaches
  • dizziness and ringing in the ears
  • muscle tremor
  • weakness and fatigue
  • rapid heart rate and quickened breathing rate
  • poor appetite, nausea, vomiting and diarrhoea
  • increased thirst, frequent urination or increased urine volume
  • irregular heart rate or rhythm
  • low blood pressure with faintness or falls
  • seizures, confusion or delirium.3

Using caffeine with other drugs

The effects of taking caffeine with other drugs – including over-the-counter or prescribed medications – can be unpredictable and dangerous, and could cause:

Caffeine + alcohol: enormous strain on the body, and can mask some effects of alcohol such as falling asleep, leading to drinking more and risk taking behaviour.

Caffeine + other stimulant drugs: increase the risk of cardiovascular problems.7


Giving up caffeine after using it for a long time is challenging because the body has to get used to functioning without it. Withdrawal symptoms usually start within 24 hours after the last dose. The symptoms can last for around 36 hours, or even longer for people who consume a lot.

These symptoms can include:

  • headache
  • marked Fatigue or drowsiness
  • dysphoric, depressed mood or irritability
  • difficulty Concentrating
  • flu-like symptoms (nausea, vomiting or muscle pain/stiffness).7
  • In Australia between 2004 and 2010, there were 297 calls to the NSW Poisons Information Line concerning toxicity from caffeinated energy drinks. The most commonly reported symptoms included palpitations/tachycardia, tremors, shaking, agitation and restlessness.10


  • Australian coffee consumption has increased from 0.5kg per person in 1940 to 2.4kg per person in 1998.9
  • According to Roy Morgan Research in the last decade coffee consumption by Australian adults has declined slowly by steadily, from 10.5 cups to 9.2 cups per week. Though, cafe visits and owning a coffee machine is on the rise.11
  • Sales of energy drinks in Australia and New Zealand increased from 34.5 million litres in 2001 to 155.6 litres in 2010.12
  1. Brands, B., Sproule, B., & Marshman, J. (Eds.). (1998). Drugs & drug abuse (3rd ed.). Ontario: Addiction Research Foundation.
  2. Food Standards Australia New Zealand. (2014). Caffeine.
  3. Upfal, J. (2006). The Australian drug guide. (7th ed.). Melbourne: Black Inc.
  4. Seifer, S., Schaechter, J., Hershorin, E. & Lepshultz, S. (2011). Health effects of energy drinks on children, adolescents, and young adults. Pediatrics, 127(3). 511–528.
  5. NPS Medicinewise. (2013). What’s the buzz with energy drinks?
  6. Nawrot, P., Jordan, S., Eastwood, J., Rotstein, J., Hugenholtz, A. & Feeley, M. (2003). Effects of caffeine on human health. Food Additives and Contaminants, 20(1). 1–30.
  7. American Psychiatric Association. (2013). Diagnostic and Statistical Manual of Mental Disorders. (5th ed). Washington: American Psychiatric Publishing.
  8. Australian Coffee Traders Association website (2006) Australian coffee stats. Retrieved August 2011
  9. Gunja, N. & Brown, J. (2012). Energy drinks: health risks and toxicity. Medical Journal of Australia. 196(1), 46–49.
  10. Australian Food News. (2014), Average Australian coffee consumption drops,but cafe visits continue to grow, research 
  11. Canadean. (2011). Canadean Soft Drink Service – Australia and New Zealand energy drink consumption volumes 1999–2016. July 2011.

Explore stimulants on the Drug Wheel

Drug wheel segment - Stimulants segment@2x.png


dehydration, dizziness, excitability, fast breathing, fast heart rate, feeling active, feeling alert, headache, higher body temperature, restlessness, stomach pains