What are the side effects of caffeine on the body?

Caffeine is widely consumed but people often don’t know the full side effects that caffeine can have on your body. Caffeine is often linked to having negative effects on the body, yet there are also some positive effects of limited caffeine consumption. It is interesting to know about so you can understand how your tea or coffee may be affecting you!

Negative side effects of caffeine from tea

What is caffeine and what is it found in?

Caffeine is a stimulant which means it makes you feel more alert and awake. Caffeine is a natural compound found in many plant sources such as coffee, cacao seeds and tea leaves. It is also found in energy drinks and cola as well as chocolate.

What is the most common source of caffeine?

Most people consume coffee or know someone who does. In the US apparently 90% of adults consume caffeine regularly (1). Coffee is one of the main ways people consume caffeine. It is recommended that one person does not consume more than 4 cups of coffee a day or 400mg/day.

How does caffeine work?

Caffeine stimulates your central nervous system as well as your heart and muscles. In the brain, caffeine acts to block a neurotransmitter known as adenosine which causes other chemicals in your brain to increase and drive stimulation of the neurons in your brain. As a result it has both positive and negative effects associated with it ...

What are the positive effects of caffeine?

Caffeine can improve memory and mood

Some findings suggest that consumption of caffeine can boost your memory. In a study where a low level of caffeine 32mg was given to male participants, there was an increase in performance in tests and elevated concentration (2). Increased stimulation in your mind from caffeine consumption can therefore have positive implications for memory, reaction times, mood etc which are all controlled in the mind.

Your metabolism could increase!

Caffeine has been suggested to be one of the few natural substances linked to fat burning. Studies have shown that caffeine can increase your metabolic rate (3, 4). It does this by increasing a hormone known as adrenaline which when travelling through the blood stream causes fats to become broken down and released into the blood. If the fat is then burnt up through exercise then there is increased fat loss.

Drinking coffee may reduce mortality

Coffee drinkers have been suggested to have far fewer diseases and potentially a lower risk of death. One study specifically looking at coffee consumption and mortality from cardiovascular disease showed that there was no associated risk of mortality in men or women and infact a potentially beneficial effect of coffee consumption (5). Coffee in particular is also high in antioxidants which contributes positively towards health and wellbeing (6).

What are the negative side effects of caffeine on the body?

Increased anxiety and your tea habit

Although low to moderate caffeine consumptions triggers increased alertness, higher doses may lead to anxiety whereby you may feel nervous or jittery. One study found that in healthy men who had 300mg of caffeine (about 3 cups) had higher stress than those who had a control drink https://www.healthline.com/nutrition/caffeine-side-effects#TOC_TITLE_HDR_2 . Infact, there is a know ‘caffeine induced anxiety disorder’ that is an acknowledges syndrome now.

Caffeine increases diuresis (the "need to wee")!

This is a common effect of caffeine consumption as caffeine acts on the bladder to stimulate it. This causes an increased need to urinate and at an increased urgency also. One study looked at the effect of caffeine on over 65,000 women and found that those who consumed higher levels of caffeine actually had an increased risk of incontinence compared to those on a lower dose (7).

Caffeine and gut problems

Caffeine in coffee has been linked to laxative effects as it causes the release of gastrin which is a hormone that drives gut activity. Increasing caffeine therefore increases movement in your gut, causing diahorrea or loose stools (8). So you may want to consider cutting back if you see any of these issues.

Headaches or caffeine migraines

Caffeine is able to trigger headaches when consumed in excess but also when undergoing withdrawal from caffeine. Caffeine can cause headaches as it leads to narrowing of blood vessels around the brain during consumption which can increase blood pressure and drive headaches. Further, when consumption stops, these vessels get bigger again and this can trigger a withdrawal headache.

Poor sleep after an evening tea

People often consume caffeine to feel awake, so it is no surprise that pumping caffeine into your body will affect your sleep. Higher levels of caffeine intake are linked to increased time needed to fall asleep and lead to a lighter sleep (9). It is however very dependent on you as an individual, with some people finding that they are more sensitive to caffeine than others. However, if you want to ensure a good night’s sleep, probably best not to have a late night tea!

Caffeine can cause high blood pressure

Several studies have highlighted that caffeine can increase blood pressure as it stimulates the nervous system (10, 11). It also seems to have the biggest effect on people who do not regularly consume caffeine. Although this effects appears to be temporary, it is important to take note of and to be aware of caffeine intake.

In summary, there are some obvious side effects from caffeine consumption. A little caffeine may have some positive effects, but it is clear moderation is important as over consumption could lead to negative side effects and even a caffeine addiction.



1. Caffeine Use Disorder: A Comprehensive Review and Research Agenda. Journal of Caffeine Research. 2013;3(3):114-30.

2. Lieberman HR, Wurtman RJ, Emde GG, Roberts C, Coviella ILG. The effects of low doses of caffeine on human performance and mood. Psychopharmacology. 1987;92(3):308-12.

3. Koot P, Deurenberg P. Comparison of changes in energy expenditure and body temperatures after caffeine consumption. Ann Nutr Metab. 1995;39(3):135-42.

4. Dulloo AG, Geissler CA, Horton T, Collins A, Miller DS. Normal caffeine consumption: influence on thermogenesis and daily energy expenditure in lean and postobese human volunteers. Am J Clin Nutr. 1989;49(1):44-50.

5. Lopez-Garcia E, van Dam RM, Li TY, Rodriguez-Artalejo F, Hu FB. The relationship of coffee consumption with mortality. Ann Intern Med. 2008;148(12):904-14.

6. Svilaas A, Sakhi AK, Andersen LF, Svilaas T, Ström EC, Jacobs DR, Jr., et al. Intakes of antioxidants in coffee, wine, and vegetables are correlated with plasma carotenoids in humans. J Nutr. 2004;134(3):562-7.

7. Jura YH, Townsend MK, Curhan GC, Resnick NM, Grodstein F. Caffeine intake, and the risk of stress, urgency and mixed urinary incontinence. J Urol. 2011;185(5):1775-80.

8. Boekema PJ, Samsom M, van Berge Henegouwen GP, Smout AJ. Coffee and gastrointestinal function: facts and fiction. A review. Scand J Gastroenterol Suppl. 1999;230:35-9.

9. Youngberg MR, Karpov IO, Begley A, Pollock BG, Buysse DJ. Clinical and physiological correlates of caffeine and caffeine metabolites in primary insomnia. J Clin Sleep Med. 2011;7(2):196-203.

10. Shah SA, Dargush AE, Potts V, Lee M, Millard-Hasting BM, Williams B, et al. Effects of Single and Multiple Energy Shots on Blood Pressure and Electrocardiographic Parameters. Am J Cardiol. 2016;117(3):465-8.

11. Riksen NP, Rongen GA, Smits P. Acute and long-term cardiovascular effects of coffee: implications for coronary heart disease. Pharmacol Ther. 2009;121(2):185-91.


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