Opiate abuse is a chronic disorder and maintaining abstinence represents a major challenge for addicts. Individuals recovering from opiate dependence have long reported that while the acute withdrawal symptoms from opiates may pass relatively quickly, they do not feel quite right for several weeks or even months thereafter. Called the “protracted abstinence syndrome,” this cluster of vague depressive-like symptoms can include reduced concentration, low energy level, poor sleep quality, and anhedonia. New data in animals now implicates the serotonin system in this phenomenon.