Drugs of abuse have very different acute mechanisms of action but converge on the brain's reward pathways by producing a series of common functional effects after both acute and chronic administration. Some similar actions occur for natural rewards as well. Researchers are making progress in understanding the molecular and cellular basis of these common effects. A major goal for future research is to determine whether such common underpinnings of addiction can be exploited for the development of more effective treatments for a wide range of addictive disorders.