Caffeine is one of the most comprehensively studied ingredients in the food supply. We know a lot about caffeine and it has been consumed safely for centuries. Caffeine exists in our diet from a variety of sources  primarily coffee, tea, chocolate, cola drinks, and both prescription and nonprescription drugs. While much is known about caffeine, many questions and misperceptions still exist; these facts and resources can help to set the story straight.

What are the effects of caffeine?

Caffeine is a mild stimulant to the central nervous system. It is not addictive, though it can be habit forming. When caffeine intake is stopped abruptly, some individuals may experience headache, fatigue or drowsiness. Age and body size can make a difference in effect. A child or a smaller person may feel caffeine's effects more strongly than an adult or a heavier, taller person. A cup of strongly brewed coffee or tea has more caffeine than a weakly brewed cup.

How much caffeine is safe?

Moderation is the key. Most experts agree that 300 mg. of caffeine (about the amount contained in 3 cups of coffee) is a moderate intake. People who have certain health problems need to check with their doctor as they consider their caffeine intake. At this time, there is NO evidence that caffeine intake is associated with heart disease, hypertension, osteoporosis or high cholesterol. Because research is ongoing, recommendations about caffeine in the presence of these conditions seems conflicting. Talk with your doctor for guidance about your consumption. Some people are more sensitive to caffeine's effects than others and may feel effects at smaller doses. Pregnancy and aging may affect one's sensitivity to caffeine. There is no evidence that caffeine in beverage form is dehydrating. Its diuretic effects are usually compensated for by the beverage's fluid content. If you ingest caffeine from sports supplements or from prescription drugs or over-the-counter sources be sure to drink adequate fluid to rehydrate yourself from caffeine's mild diuretic action.

Will caffeine help me study?

Caffeine may help you stay awake and be alert to study, but it will not improve your performance on an exam the next day if you have not gotten enough rest or are exhausted from an all-nighter.

How can I energize?

Instead of reaching for another soda or coffee, try these non-caffeinated strategies to maintain good energy levels:

Can I safely have caffeine if I am pregnant or if I am considering pregnancy?

At this time, moderate caffeine intake is not believed to affect either fertility or the health of a mother or fetus. Talk with your doctor; research is always in progress. Avoid high consumption. Try to limit coffee to three cups per day or less. Caffeine is passed into breast milk and little data exists about the effects on infants. Try to avoid this while breastfeeding.

I Get My Caffeine from Coffee and/or Herbal Supplements - and I Would Like to Lose Weight. Is it Safe to Take an Herbal Supplement to Help Me Lose Weight or to Stay Awake?

Herbal supplements for weight loss often contain high levels of caffeine and/or guarana or ephedra (ma huang) - other nervous system stimulants. Using weight loss supplements containing ephedra have been associated with illness and death. For additional ephedra information visit the U.S. Food and Drug Web site and search for "dietary supplements."

Taking diet supplements containing these ingredients, and maintaining your usual caffeine intake can push you past the recommended moderate level of caffeine intake. Remember the "moderate" caffeine limit is 300 mg/day - and realize that herbal stimulants can be very dangerous.

If your caffeine comes from pills vs. drinks, be sure to keep your fluid intake high to address the moderate dehydrating effects of caffeine.

How can I quit or reduce my caffeine consumption?

The amount of caffeine in some common foods and beverages is as follows:

Some common brands of medication that contain caffeine are:

For additional information on caffeine, visit the MedLine Plus Web site and search for "drugs & supplements, then caffeine."