All addictive drugs have two things in common.
They produce an initial pleasurable effect, followed by a rebound unpleasant effect. Alcohol and other drugs produce a positive feeling at first, but when this effect wears off, it leaves a person with opposite feelings of depression and irritability. This happens because of the suppression of the normal production of chemicals in the brain, which ordinarily produce feelings of pleasure. With suppression, the brain then goes into a state of depression. Figure 1 is a simplified way of looking at the brain's Normal Reward System .