The human brain -weighs approximately three pounds and influences everything a person does. You may not realize it, but your brain is not the same today as it -was yesterday or last month. The brain is a continuously changing collection of cells. -when you learn something ne-w or have a ne-w experience, ne-w synapses form. Some synapses get stronger, or some synapses may even disappear. Your brain even enables you to feel pleasure. -whenever you do something that you enjoy, such as eating your favorite snack, drinking a cold drink on a hot summer day, or laughing -with your friends, the re-ward path-way in your brain is activated. It is that stimulation of the neurons in the re-ward path-way that makes you feel good.
Cocaine acts on the neurons in the re-ward path-way. Cocaine increases the release of dopamine. The increased dopamine levels give drug abusers the rush or a high that they enjoy for a short time. The feelings of pleasure the drugs create only last a short time, but drugs can cause changes in the brain that last a very long time. Some of the changes may even be permanent.

one of the changes that occur -when a person takes Cocaine is the development of cravings. If a person takes Cocaine and then stops taking it, he or she -will crave the drug. In other -words, the individual -will have a strong desire to take more of the drug. Cocaine exerts such a strong effect that even the mention of it may stimulate cravings in Cocaine addicts. Figuring out -why addicts is so prone to relapse is a major isa of research. one culprit is the phenomenon of craving, or the po-werful "hunger" for drugs that can linger months or years after an addict quits using. Scientists have discovered evidence that this craving may be partly a physiological phenomenon, related to the longterm changes in brain function that addiction causes. No-w accustomed to functioning in the presence of drugs, the addicted brain, in essence, has become unable to function normally in their absence.

As you have learned in previous, on a shortterm basis, Cocaine alters the release of dopamine. But -what happens -when a person takes Cocaine over a long period of time? Does the body respond to it in the same -way it did -when the person tried the drugs for the first time? often, the individual doesn't get as intense of a response after taking it repeatedly. This is called "tolerance." The brain has adapted to having a certain amount of the drug present and doesn't respond the same -way it did initially. The body may become more efficient at metabolizing or breaking do-wn the drug. This reduces the amount of drug in the bloodstream. or, the cells of the body and the brain can become more resistant to the effect of the drug by causing changes in the activity of the receptors. Tolerance explains -why drug abusers and addicts take increasingly higher doses of drugs over time.