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. It is part of the same group of drugs sometimes used to treat asthma. Caffeine is defined as a drug because it stimulates the central nervous system, causing increased heart rate and alertness. Most people who are sensitive to caffeine experience a temporary increase in energy and elevation in mood.

Caffeine is present in tea leaves, coffee beans, chocolate, many soft drinks, pain relievers, and other over-the-counter pills. In its natural form, caffeine tastes very bitter. But most caffeinated drinks have gone through enough processing to camouflage the bitter taste. Most teens get the majority of their caffeine intake through soft drinks, which can also have added sugar and artificial flavours.

If taken in moderate amounts (like a single can of soft drink or cup of coffee), many people feel that caffeine increases their mental alertness. But higher doses of caffeine can cause anxiety dizziness, headaches, and the jitters and can interfere with normal sleep. Very high doses of caffeine - like drinking multiple energy drinks can be very harmful to the body, even causing death.

Caffeine is addictive and may cause withdrawal symptoms for those who abruptly stop consuming it. These include severe headaches, muscle aches, temporary depression, and irritability. Although scientists once worried that caffeine could stunt growth, this concern is not supported by research.

Caffeine sensitivity refers to the amount of caffeine that will produce an effect in someone. This amount varies from person to person. On average, the smaller the person, the less caffeine necessary to produce side effects. However, caffeine sensitivity is most affected by the amount of daily caffeine use. People who regularly drink beverages containing caffeine soon develop a reduced sensitivity to caffeine. This means they require higher doses of caffeine to achieve the same effects as someone who doesn't drink caffeinated drinks every day. In short, the more caffeine you take in, the more caffeine you'll need to feel the same effects.

Caffeine moves through the body within a few hours after it's consumed and is then passed through the urine. It's not stored in the body, but you may feel its effects for up to 6 hours if you're sensitive to it. Although you may think you're getting plenty of liquids when you drink caffeinated beverages, caffeine works against the body in two ways. It has a mild dehydrating effect because it increases the need to urinate. And, secondly, large amounts of caffeine may cause the body to lose calcium and potassium, causing sore muscles and delayed recovery times after exercise.

Medically, caffeine is useful as a cardiac stimulant and also as a mild diuretic (it increases urine production). Recreationally, it is used to provide a "boost of energy" or a feeling of heightened alertness. It is often used to stay awake longer by college students when revising for exams, and drivers use it to stay awake late when on a night trip. Many people feel as though they cannot function effectively in the morning without a cup of coffee to wake them up. Those who feel this way may be addicted to caffeine.

Caffeine operates using the same neuro-chemical mechanisms that amphetamines, cocaine and heroin use to stimulate the brain, although its effects are milder. One cup of coffee may stimulate the senses, but regular intake of caffeine can leave people suffering from a range of different health symptoms. Caffeine stimulates the central nervous system, increasing the stress hormones in the blood stream and making a person unnaturally alert. This induced alert state tends to subdue the body’s natural instincts and prevent it from relaxing, which leads to undue stress and various disorders.
Daily caffeine intake induces a 24 hour cyclic disturbance in your body.  Even if endless cups of coffee are used to prevent fatigue in the day, it can lead to an inevitable collapse in the evening. Irritability, gloom and fatigue along with an uncomfortable sensation are the usual symptoms and insomnia at night. By the next morning, users can be so tired that they want more caffeine to settle their mood.