The human body produces approximately 10–80 mcg of melatonin per night. Oral melatonin is poorly absorbed (bioavailability is commonly estimated at around 15%), so 0.8 mg delivers roughly 120 mcg to the bloodstream: a few times the body’s own output, and well below what a typical 3,000–5,000 mcg (3–5 mg) capsule delivers. Sleep uses Melotime®, a sustained-release form. In a head-to-head pharmacokinetic study the sustained-release capsule produced half the peak level of an immediate-release capsule, and its half-life was about 5 hours against 1 hour for immediate-release (Thanawala et al., Pharmaceutics, 2024). A lower level is kept going later into the night instead of arriving in one spike. An umbrella review of melatonin efficacy found evidence that melatonin supports sleep onset (Low et al., J Psychiatr Res, 2020). That review covers melatonin and melatonin agonists in insomnia generally; most of the trials in it used higher doses than 0.8 mg, so it speaks to melatonin’s effect rather than to this specific dose.

Glycine is an inhibitory neuromodulator that has been studied for its ability to lower core body temperature at bedtime — a physiological cue that facilitates sleep onset. Human trials of glycine supplementation (3 g before bed) have reported improvements in subjective sleep quality, reduced time to sleep onset, and decreased next-day fatigue (Inagawa et al., 2006; Yamadera et al., 2007; reviewed in Bannai et al., 2012). The 2,400 mg dose in Sleep (which counts the glycine carried by the magnesium chelate) is close to the 3 g dose used in those trials.

Magnesium bisglycinate provides elemental magnesium in a fully chelated form (each magnesium bound to two glycine molecules) that does not cause the laxative effect associated with magnesium citrate or oxide. A systematic review found magnesium status was associated with sleep quality in observational studies, while randomised trials of supplementation reported contradictory findings (Arab et al., Biol Trace Elem Res, 2023). A 2025 RCT of 155 participants found magnesium bisglycinate significantly improved sleep quality scores versus placebo (Schuster et al., Nat Sci Sleep, 2025). The chelate also carries glycine, which is counted within the 2,400 mg of glycine on the label.

Each ingredient in Sleep targets a distinct physiological pathway: Melatonin provides the circadian timing signal that tells the brain it is night. Glycine reduces core body temperature via peripheral vasodilation — a known facilitator of sleep onset — and improves sleep architecture quality. Magnesium bisglycinate supports muscular and neurological relaxation and reduces sleep-onset latency. A single high-dose melatonin product addresses only the first pathway; these three ingredients address all three in one formula.