University Health Service

Coffee cup filled with coffee. Cream and sugar. Coffee beans in the background.

What is caffeine? 

Caffeine is a plant product that is most commonly found in coffee beans, tea, soft drinks, cocoa and chocolate. Caffeine is also found in some prescription and non-prescription drugs, including cold, allergy and pain relievers.

How caffeine affects the body:

Caffeine acts as a stimulant by exerting an effect on the central nervous system. The effects of caffeine on the body may begin as early as 15 minutes after ingesting and last up to six hours.

Caffeine is recognized as an addictive substance by the World Health Organization (WHO); for more, see Fact Sheet from Johns Hopkins

When consumed in moderate doses (up to 250 mg, or about two 6-oz cups of coffee or about four 12-oz colas), caffeine can help people feel more alert and less sleepy. Most individuals consuming moderate amounts will experience few, if any, negative side effects.

Caffeine may increase heart rate, body temperature, blood flow to the skin & extremities, blood pressure, blood sugar levels, stomach acid secretion and production of urine (diuretic). People may experience dizziness, hypoglycemia, fruit-like breath odor, troubled breathing, muscle tremors, nausea, diarrhea, increased urine, ketones in urine,drowsiness, thirst, anxiety, confusion, irritability, insomnia, changes in appetite, dry mouth, blurred vision, and cold seats.

Contrary to popular belief, drinking coffee will not help someone who is intoxicated become sober.

Side effects:

While consuming moderate amounts of caffeine does not seem to have long-term detrimental effects, consuming larger amounts of caffeine (1000 mg or about ten 6-oz cups of coffee a day) on a regular basis  may be linked to conception problems, increased episodes of heartburn, and changes in bowel habits.

Too much caffeine may lead to sleep deprivation and a tendency to disregard the normal warning signals that the body is tired and needs rest. Caffeine does not replenish energy or prevent emotional fatigue; food and sleep are the only remedies for these. When normal sleeping patterns are continually disrupted, mood depression may occur. Too much caffeine may also lead to anxiety-related feelings such as excessive nervousness, sweating and tremors.

People who take medications for depression, anxiety or insomnia, high blood pressure, other heart problems, chronic stomach upset or kidney disease should limit caffeine until discussing the matter with a clinician.

If you want to avoid some of the annoying side effects of caffeinated beverages (e.g., jitters or sleeplessness), switching to decaffeinated drinks may help.

Effects of quitting:

People who stop drinking caffeinated drinks may notice several side effects, especially if they are used to consuming large amounts of caffeine. Some symptoms of caffeine withdrawal include headaches, irritability, nervousness, nausea, constipation and muscular tension. These symptoms usually appear about 12-24 hours after someone has stopped consuming caffeine and usually last about one week. It is recommended that you gradually decrease your caffeine intake to avoid withdrawal symptoms. 

Caffeine during pregnancy:

Some studies show an association between high doses of caffeine and an increased rate of miscarriages, premature deliveries or low birth weights. However, complicating factors such as smoking and alcohol use were not accounted for in these studies. In high doses, caffeine can affect fetal breathing and heart rate.

If you are pregnant, or planning to become pregnant, consider your options (e.g. eliminating caffeine or limiting intake to 200-300 mg per day). Discuss these options with your clinician.

Caffeine contents:

The Center for Science in the Public Interest lists caffeine content of food, drink and non-prescription drugs.

Caffeine Informer provides a fun calculator and other tools.

For coffee, caffeine content varies depending on type of bean, quantity used, how finely beans are ground and brewing time.

For non-prescription drugs, it's a good idea to read labels.

More information:

UHS offers nutrition consultation. See Nutrition Clinic or call (734) 763-3760.

See also Medline Plus