Endogenous Opiates and Behavior: 2016

•This is the 39th annual review of research concerning the endogenous opioid system.•It reviews 2016 papers about opioid peptides and receptors and their analgesic roles.•It reviews 2016 papers about opioid roles in stress, tolerance, dependence and abuse.•It reviews 2016 papers about opioid roles in learning, ingestion, hormones and mood.•It reviews 2016 papers about opioid roles in activity, immune and other bodily function. This paper is the thirty-ninth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2016 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.