Melatonin supplements are meant to kick-start your body's 'sleepiness' stage: the point in the day when you begin to feel the need for rest. The brain's pineal gland naturally produces melatonin at night and maintains those levels in the bloodstream for about 12 hours; once they lower, we wake up and go about our business. In the daytime, we have very little melatonin in our bodies at all. This is why it's important to take melatonin 90 minutes to two hours before your conventional bedtime, to allow it to get into the bloodstream and perform its signaling magic.

Magnesium, meanwhile, operates in a different way. It's responsible for increasing your sleep, Healthline says, by "activating the parasympathetic nervous system, the system responsible for getting you calm and relaxed." It does this through both neurotransmitters, which dampen nerve activity, and our friend melatonin. Magnesium and melatonin levels in the brain tend to correlate; low levels of both and you're awake, high levels and you're asleep. Magnesium appears to regulate melatonin's production while also operating as a dampener on the nervous system signals that might keep you awake. It's basically like your brain putting on earmuffs.

While magnesium and melatonin are interrelated, they work in quite different ways to regulate the body's sleep-wake cycle. Every cell in your body has a 24-hour clock in it, and uses that clock to regulate things like appetite, metabolism and yes, sleep. A study in 2016 found that magnesium has a key role in that 'body clock' in our cells, helping them all stay on track and act in concert to help us maintain a 24-hour cycle. Having magnesium in your body doesn't just affect your brain; it influences all your cells.

Melatonin is a part of that cycle too, but it's role is much more specific. Whenever our retina senses light, the National Sleep Foundation explains, it "stimulates a nerve pathway from the retina in the eye to an area in the brain called the hypothalamus. There, a special center called the suprachiasmatic nucleus (SCN) initiates signals to other parts of the brain that control hormones, body temperature and other functions that play a role in making us feel sleepy or wide awake." It's the SCN that activates the pineal gland at night to produce melatonin and herald sleepiness.

Both magnesium and melatonin supplements aim to create the urge for sleepiness — that nodding-off feeling that signals you're falling asleep. But how do they effect sleep quality itself? Studies show that both are linked to an increase in more restful sleep, but in different ways.

The Sleep Doctor, Dr. Michael Breus, writes that melatonin has been shown in studies to make people sleep more refreshing. Melatonin, he says, may "improve the quality of sleep and reduce daytime sleepiness and fatigue. Studies also show melatonin may increase REM sleep." REM sleep is the period in our sleep cycle where we dream, occurring roughly once every 90 minutes or so throughout the night, and is key to neural functions like preservation of memories.

Magnesium, meanwhile, doesn't seem to reduce daytime fatigue, but studies in 2011 and 2012 do show that magnesium leaves people feeling more rested after a night's sleep. There are no studies to show that magnesium does anything to REM sleep, but anecdotal evidence reported by Men's Health suggests that people who take it do have vivid dreams, suggesting it may affect or lengthen REM cycles.

Both magnesium and melatonin are marketed in the United States as supplements, which are not heavily regulated by the FDA. "While melatonin appears to be effective for some people, experts warn against expecting too much," the sleep organization Tuck wrote. "No long-term safety data exist, and the optimum dose and formulation for any application remains to be clarified." Studies on melatonin are ongoing, but the lack of regulation on its dosage means that it can be available in extremely high quantities that aren't actually necessary for sleep. Long-term excessive usage has been tied to fertility and reproductive issues in both men and women, though there needs to be more evidence to support this.

Overdoses of magnesium are serious, but in different ways. The Office of Dietary Supplements at the National Institutes of Health notes that "high doses of magnesium from dietary supplements or medications often result in diarrhea that can be accompanied by nausea and abdominal cramping." Magnesium toxicity is also possible, though often the liver manages to rid the body of the bulk of excess magnesium (which, again, we get naturally in our diets without supplementation) before it can cause serious damage.

The "correct" dosage of melatonin and magnesium can be tricky. "90 percent of the melatonin that's sold currently is sold in an overdosage format," Dr. Breus recently told Bustle. "The appropriate dose is somewhere between a half and one and a half milligrams. [....] almost nobody sells it at that. They sell it at three, five, even 10." This means that if you're taking melatonin, you may be taking too much without knowing it.

Taking the right magnesium supplement, meanwhile, depends on multiple factors, including how much melatonin you already get in your diet and whether you have illnesses like diabetes, which can affect magnesium levels. Healthline also says that magnesium supplements come in many different forms, including magnesium oxide and magnesium gluconate, which have different absorption rates. Identifying the right dosage for sleep issues probably means talking to a doctor.

Both magnesium and melatonin have a lot of potential to increase your sleep quality and help you drop off. However, while they're both naturally-occurring, they're not the same — so don't get them confused.