It's 11 PM and Aaron has already had a full day of school, work, and after-school activities. He's tired and knows he could use some sleep. But he still hasn't finished his homework. So he reaches for his headphones — and some caffeine.

What Is Caffeine?

Caffeine is a drug that is naturally produced in the leaves and seeds of many plants. It's also produced artificially and added to certain foods. Caffeine is defined as a drug because it stimulates the central nervous system, causing increased alertness. Caffeine gives most people a temporary energy boost and elevates mood.

Caffeine is in tea, coffee, chocolate, many soft drinks, and pain relievers and other over-the-counter medications. In its natural form, caffeine tastes very bitter. But most caffeinated drinks have gone through enough processing to camouflage the bitter taste.

Teens usually get most of their caffeine from soft drinks and energy drinks. (In addition to caffeine, these also can have added sugar and artificial flavors.) Caffeine is not stored in the body, but you may feel its effects for up to 6 hours.

Got the Jitters?

Many people feel that caffeine increases their mental alertness. Higher doses of caffeine can cause anxiety, dizziness, headaches, and the jitters. Caffeine can also interfere with normal sleep.

Caffeine sensitivity (the amount of caffeine that will produce an effect in someone) varies from person to person. On average, the smaller the person, the less caffeine needed to produce side effects. Caffeine sensitivity is most affected by the amount of caffeine a person has daily. People who regularly take in a lot of caffeine soon develop less sensitivity to it. This means they may need more caffeine to achieve the same effects.

Caffeine is a diuretic, meaning it causes a person to urinate (pee) more. It's not clear whether this causes dehydration or not. To be safe, it's probably a good idea to stay away from too much caffeine in hot weather, during long workouts, or in other situations where you might sweat a lot.

Caffeine may also cause the body to lose calcium, and that can lead to bone loss over time. Drinking caffeine-containing soft drinks and coffee instead of milk can have an even greater impact on bone density and the risk of developing .

Caffeine can aggravate certain heart problems. It may also interact with some medications or supplements. If you are stressed or anxious, caffeine can make these feelings worse. Although caffeine is sometimes used to treat migraine headaches, it can make headaches worse for some people.

Moderation Is the Key

Caffeine is usually thought to be safe in moderate amounts. Experts consider 200-300 mg of caffeine a day to be a moderate amount for adults. But consuming as little as 100 mg of caffeine a day can lead a person to become "dependent" on caffeine. This means that someone may develop withdrawal symptoms (like tiredness, irritability, and headaches) if he or she quits caffeine suddenly.

Teens should try to limit caffeine consumption to no more than 100 mg of caffeine daily, and kids should get even less. The following chart includes common caffeinated products and the amounts of caffeine they contain:

Source: U.S. Food and Drug Administration, National Soft Drink Association, Center for Science in the Public Interest.

Cutting Back

If you're taking in too much caffeine, you may want to cut back. The best way is to cut back slowly. Otherwise you could get headaches and feel tired, irritable, or just plain lousy.

Try cutting your intake by replacing caffeinated sodas and coffee with noncaffeinated drinks. Options include water, decaffeinated coffee, caffeine-free sodas, and caffeine-free teas. Start by keeping track of how many caffeinated drinks you have each day, then substitute one of these daily drinks with a caffeine-free alternative. Continue this for a week. Then, if you are still drinking too much caffeine, substitute another of your daily drinks, again, keeping it up for a week. Do this for as many weeks as it takes to bring your daily caffeine intake below the 100-milligram mark. Taking a gradual approach like this can help you wean yourself from caffeine without unwanted side effects like headaches.

As you cut back on the amount of caffeine you consume, you may find yourself feeling tired. Your best bet is to hit the sack, not the sodas: It's just your body's way of telling you it needs more rest. Your energy levels will return to normal in a few days.

Reviewed by: Mary L. Gavin, MD
Date reviewed: October 2011