Melatonin vs magnesium — which is better for sleep?

For sleep specifically, melatonin has the more direct evidence: multiple meta-analyses of placebo-controlled trials find it shortens time to fall asleep by roughly 5-12 minutes and modestly increases total sleep time, with effects peaking around 4mg taken close to bedtime. Magnesium's evidence base is just as large, but its strongest, most consistent findings are for blood pressure and type 2 diabetes risk — for its most commonly marketed use, sleep, the evidence is explicitly weaker (a Cochrane review found limited support). If sleep onset is the actual goal, melatonin is the better-targeted choice; magnesium may still be worth taking, just less for the reason it's usually sold.