Updated June 12, 2014.
Written or reviewed by a board-certified physician. See About.com's Medical Review Board.
Question: What are the Side Effects of Caffeine?
I started a new job a few months ago, and my office is right next to a gourmet coffee house. I get invited to go there a few times a day by my co-workers, but so far I've passed, because I'm not sure whether there are side effects to drinking a lot of coffee. Are there any recognized side effects of caffeine?
Answer:
Caffeine is so common in American society, you can easily forget that it is an addictive drug.
Office workers are particularly prone to habitual coffee drinking, as it helps to keep you alert and ward off fatigue. Some people even think caffeine improves their memory, although the research evidence for this is mixed.
But there certainly are recognized side effects of caffeine. The following side effects of caffeine intoxication are even included in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), the gold standard for diagnosing mental health problems.
Short-Term Side Effects of Caffeine
- Restlessness -- this is basically difficulty relaxing and calming yourself down.
- Nervousness -- this is a sense of mental uneasiness, a kind of restlessness of the mind, that often goes hand in hand with anxiety.
- Excitement -- although excitement is often a positive experience, after too much caffeine, you can get overly excited about trivial events, which can be awkward in social situations.
- Insomnia -- this can manifest in many different ways, but overall, it adds up to having difficulty getting enough sleep.
- Flushed Face -- a red face at work might make you look embarrassed, and can be embarrassing!
- Diuresis -- another embarrassing side effect of too much caffeine, you can end up running to the bathroom and urinating more fluid than you consumed.
- Gastrointestinal Disturbance -- there are a range of gastrointestinal disturbances that can be side effects of too much caffeine, including stomachache, gas, heartburn, constipation, diarrhea, nausea and vomiting. However, while stomachaches are quite common after a lot of coffee, vomiting is quite rare, and if you have this reaction, you should avoid caffeine completely until you have discussed this with your doctor.
- Muscle Twitching -- involuntary muscle twitches are an annoying side effect of caffeine for some people, but there are other causes, so try abstaining from caffeine if this is an ongoing problem for you, and see if the twitching subsides. If it does not, talk to your doctor about treatment for this common problem.
- Rambling Flow of Thought and Speech -- this is a common side effect of stimulant drugs and is often more annoying to the listener than to the speaker. But be aware that getting over-stimulated on coffee and dominating conversations might undermine your popularity at work.
- Tachycardia or Cardiac Arrythmia -- these side effects are changes to the speed and regularity of your heartbeat, and are certainly a cause for concern. Stop using caffeine and see your doctor if you think your heartbeat is abnormal, particularly if you feel it is excessively rapid or irregular.
- Periods of Inexhaustability -- although this side effect may seem desirable, we all need rest. If you are unable to tire enough to get adequate rest, you can run yourself down, and not give your body adequate time to repair itself. You may not feel exhausted, but your body will become worn out without regular breaks from activity.
- Psychomotor Agitation -- this is a kind of physical fretfulness that makes it difficult to calm your body.
Research has shown that many people are unaware of these side effects, and a good deal of the research into caffeine has lauded the positive short-term effects, such as increased attention and energy, without taking these health effects into account.
Sources:
Derbyshire, E. & Abdula, S. "Habitual caffeine intake in women of childbearing age," J Hum Nutr Diet 21:159–164. 2008.
Diagnostic and Statistical Manual of Mental Disorders, Text Revision, Fourth Edition, American Psychiatric Association. 2000.
Farag, N., Whitsett, T., McKey, B., Wilson, M., Vincent, A., Everson-Rose, S., and Lovallo, W. "Caffeine and blood pressure response: sex, age, and hormonal status," Journal of Women's Health 19:1171-1176. 2010.