Obesity is frequently framed as an addictive disorder, but scientists understand little about what first prompts the compulsion to eat. Now a study at Tufts University suggests that the impulse could be hardwired. In addicts of any type, the brain’s signaling of dopamine—a chemical involved in motivation and reward—becomes abnormal over time. The Tufts study shows, however, that rats prone to obesity are born with low dopamine levels. Eating, then, is akin to self-medication because it helps to restore the chemical to healthy levels; obesity may simply be a side effect that develops from this self-remedy over time. The findings also raise the question of whether animals born prone to obesity could be at a heightened risk for developing addictions to drugs that stimulate dopamine function, such as cocaine and amphetamines.