Among the many hormones pumped through the body, the suprachiasmatic nuclei (SCN) controls the production of the one that makes people want to curl up in a ball on the nearest couch and catch a few zzzs. Melatonin is a naturally occurring chemical that helps regulate the circadian rhythm. The more of it that the body produces, the more likely you are to get sleepy [source: EarthSky].
Your melatonin production schedule varies based on light. Remember that the SCN is located just above the optic nerve, which sends information from the eyes to the brain. The less light that comes in – after the sun goes down and the sky becomes dark, for example – the more melatonin the SCN tells the brain to make [source: University of Maryland].
Some folks who suffer from sleep disorders will pop melatonin pills to help them get some rest. The effect of these supplements, which are available without a prescription and not regulated in the same way as pharmaceutical drugs, is still not clear. Experts warn that users should be careful to monitor the size and timing of doses so as not to throw off their natural body clocks [source: National Sleep Foundation].