How Addiction Affects the Brain
What happens physically—in the brain and body—when one is addicted? Drugs have three basic effects on the body:

stimulation or a feeling of being “high” or energized
depression or a feeling of being calm or even sleepy
distortion of the senses
When any chemical enters the brain, it is absorbed into the brain through receptor sites. When the body is getting a drug from an outside source, the brain stops making some of its own chemicals, such as dopamine and endorphins, that is makes naturally. The brain then becomes dependent on the outside source of drugs. At the same time, as the brain adapts to the drug’s presence, the individual using the drugs must take more and more of most addicting drugs to try to reach the same feelings that they got when they first started using the drugs. (However, they almost never can get that initial feeling again.)