Melatonin influences the central nervous system to regulate wakefulness and sleepiness, associating it with the dark phase of the 24-hour cycle.

“For people that are not pregnant, in fact, all people, melatonin has a powerful effect on the central nervous system as a whole. Your brain and spinal cord are the major components of your central nervous system , and melatonin, because it's associated with darkness, which is just another way of saying that light suppresses melatonin, melatonin is thereby associated with the dark phase of each 24-hour cycle, it can have a number of different effects in terms of waking up or making our body feel more sleepy. And it does that by way of impacting cells within our nervous system, literally turning on certain brain areas, turning off other brain areas.”