Interacts specifically with a number of opioid ligands. Receptor for neuropeptides B and W, which may be involved in neuroendocrine system regulation, food intake and the organization of other signals. Detected at high levels in caudate nucleus, hippocampus and amygdala; at moderate levels in the adult brain, thalamus, parietal cortex, pituitary gland, adrenal gland and lymph nodes. Belongs to the G-protein coupled receptor 1 family.