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 osteoporosis. 

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. 

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. Examples include water, caffeine-free sodas, and caffeine-free teas. Keep track of how many caffeinated drinks  you have each day, and substitute one drink per week with a caffeine-free alternative until you've gotten below the 100-milligram mark. 

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.