Caffeine is a central nervous stimulant. Considered the most widely used psychoactive drug in the world, caffeine is also considered by some to be the most widely abused drug in the world. Here are some of the effects of caffeine on the central nervous system.

Your Body and Caffeine Absorption

Caffeine is water soluble and passes easily through cell membranes, which means that your body absorbs this drug very quickly. Caffeine passes directly into the bloodstream through your stomach and travels first to the brain, then to the reproductive organs and liver.

Because caffeine is so easily absorbed and distributed throughout all the cells of your body, it's very difficult for your liver and kidneys to remove it from your system. If you drink one cup of coffee, the caffeine from that coffee will remain in your body for several days. If you're a habitual caffeine user, it's likely that every cell of your body contains caffeine.

Caffeine and Adenosine

Caffeine is chemically similar to adenosine, a type of sugar that plays a central role in providing energy to your body's cells. Adenosine also plays a role in the transmission of nerve signals. When adenosine attaches itself to neural receptors in your brain, you begin to feel lethargic and sleepy. Adenosine also has the following effects on your body:

• It helps ease the effects of stress
• It lowers heart rate and blood pressure
• It lowers body temperature
• It causes blood vessels to dilate
• It slows digestion

Caffeine, because it's similar to adenosine on a chemical level, attaches itself to the same neural receptors that adenosine does. When caffeine binds itself to these neural receptors, it blocks adenosine so that it cannot affect your central nervous system.

How Caffeine Affects Your Central Nervous System

Caffeine affects your central nervous system differently from the way adenosine does, even though it attaches itself to the same neural receptors. Caffeine causes your neurons to fire more rapidly, hence its well known stimulating effects.

Caffeine continues to affect your brain as long as it remains in your blood. While the average half life of caffeine in the adult bloodstream is about four hours, the length of time can vary considerably depending on the metabolism of the caffeine user. Those with low metabolisms will feel the effects of caffeine for much longer than those with high metabolisms. Nicotine also has an effect on caffeine metabolism. Smokers metabolize caffeine twice as fast as non smokers.

Caffeine has been shown to act on the part of the brain that's sensitive to levels of carbon dioxide in your blood. That's why caffeine is often included as an ingredient in over the counter cold remedies. Caffeine makes your brain even more sensitive to levels of carbon dioxide in the blood, which causes increased depth of breathing and therefore higher levels of blood oxygen. While this makes caffeine an effective treatment for those who suffer from breathing problems and breathlessness, it can also lead to hyperventilation if too much caffeine is consumed.