The multiple facets of opioid receptor function: implications for addiction.

Addiction is characterized by altered reward processing, disrupted emotional responses and poor decision-making. Beyond a central role in drug reward, increasing evidence indicate that opioid receptors are broadly involved in all these processes. Recent studies establish the mu opioid receptor as a main player in social reward, which attracts increasing attention in psychiatric research. There is growing interest in blocking the kappa opioid receptor to prevent relapse, and alleviate the negative affect of withdrawal. The delta opioid receptor emerges as a potent mood enhancer, whose involvement in addiction is less clear. All three opioid receptors are likely implicated in addiction-depression comorbidity, and understanding of their roles in cognitive deficits associated to drug abuse is only beginning.