**7.12 Melatonin**

Some studies show that melatonin, an hormone for regulating mammalian circadian biology exerts anti-nociception effects in animal models and humans, and a recent metanalysis strongly supports the utilization of melatonin on antinociception against many types of pain [95]; thus, suggesting that melatonin directed to comorbid condition should be effective without any major adverse effects.
