These days it seems as if everyone is addicted— not just to heavy drugs such as cocaine but also to newly claimed obsessions such as eating, gambling, and the Internet. In his lab at the University of Texas Southwestern Medical Center, molecular psychiatrist Eric Nestler is making progress in understanding the nature of addiction and the strong similarities between different kinds of cravings. His studies show how a protein called delta-FosB modulates the brain's sensitivity to drugs, raising hopes of medical treatments that could set addicts free. Nestler discussed the science of need with Discover reporter Jocelyn Selim.