The human body produces approximately 10–80 mcg of melatonin per night. In a study of 2 mg and 4 mg tablets, only about 15% of an oral dose reached the bloodstream (DeMuro et al., J Clin Pharmacol, 2000); applied to 0.8 mg, that is an estimated 120 mcg: 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 study of 5 mg capsules (funded by the ingredient’s manufacturer, with two authors employed by it), 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). That study did not test Sleep’s 0.8 mg dose. 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 pooled studies of melatonin and similar drugs in people with poor sleep; most 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. In rats, it lowered core body temperature, which the researchers suggest may be one way it helps sleep begin (Bannai & Kawai, J Pharmacol Sci, 2012). 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; 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). 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). In a 2025 randomised trial of 155 adults reporting poor sleep, 250 mg of magnesium a day as bisglycinate (not the 126 mg in Sleep) for 4 weeks improved scores on a sleep-difficulty questionnaire slightly more than placebo (a small effect); a single-question sleep quality rating did not differ significantly (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 lowered core body temperature in rats, a possible way it helps sleep begin, and in small human trials improved how people rated their sleep. Magnesium bisglycinate supports muscular and neurological relaxation; in two small magnesium oxide trials, people fell asleep about 17 minutes sooner than with placebo, with low to very low quality evidence, and neither trial used the form or dose in Sleep (Mah & Pitre, 2021). A single high-dose melatonin product addresses only the first pathway; these three ingredients address all three in one formula.