Pain control by melatonin: Physiological and pharmacological effects.

Pain and anxiety are the most common neurological responses to many harmful or noxious stimuli and their management clinically is often challenging. Many of the frequently used morphine-based drugs, non-steroid anti-inflammatory drugs and acetaminophen, while efficient for treating pain, lead to patients suffering from several unwanted side effects. Melatonin, produced from the pineal body is a hormone of darkness, is involved in the control of circadian rhythms, and exerts a number of pharmacological effects. Melatonin mediates its actions through MT1/MT2 melatonin receptors on the cell membrane and also through RZR/ROR nuclear orphan receptors. Chronic pain syndromes are often associated with the desynchronization of circadian and biological rhythms, which also cause disturbances in the sleep-wake cycle. Melatonin-mediated analgesic effects seem to involve β-endorphins, GABA receptor, opioid receptors and the nitric oxide-arginine pathway. The effectiveness of melatonin as an analgesic and anxiolytic agent has been demonstrated in various animal models of pain and this led to the use of melatonin clinically in different pathological conditions and also in patients undergoing surgery. Melatonin was found to be effective in many of these cases as an anxiolytic and analgesic agent, indicating its clinical application.