POMC and cancer: But, unfortunately, opioid analgesics often produce poor pain relief against neuropathic cancer pain and also induce adverse side effects such as hormone (e.g., ACTH, cortisol, LH and testosterone) secretion, neurotransmitter (e.g., nicotine, adenosine, GABA and cholecystokinine) release, feeding, gastrointestinal motility, and respiratory activity [5].