The Addicted Brain; March 2004; Scientific American Magazine; by Eric J. Nestler and Robert C. Malenka; 8 Page(s)

White lines on a mirror. A needle and spoon. For many users, the sight of a drug or its associated paraphernalia can elicit shudders of anticipatory pleasure. Then, with the fix, comes the real rush: the warmth, the clarity, the vision, the relief, the sensation of being at the center of the universe. For a brief period, everything feels right. But something happens after repeated exposure to drugs of abuse - whether heroin or cocaine, whiskey or speed.

The amount that once produced euphoria doesn't work as well, and users come to need a shot or a snort just to feel normal; without it, they become depressed and, often, physically ill. Then they begin to use the drug compulsively. At this point, they are addicted, losing control over their use and suffering powerful cravings even after the thrill is gone and their habit begins to harm their health, finances and personal relationships.