Nutricost Glycine Powder Review

Yes on both. Nutricost includes a measuring scoop in the tub and portions the serving at 3 g of free-form glycine — the exact dose used in the human sleep studies (Yamadera 2007; Bannai 2012, PMID 22529837). So you get the studied dose without measuring by eye: one scoop into water or warm tea, 30 to 60 minutes before bed. That included scoop is the main practical reason to pick this over a bare bulk bag.

It is 100% plain glycine — non-GMO and gluten-free, no fillers, no blend. The sleep evidence is for glycine by itself, so anything labeled 'glycine complex,' NAC+glycine, or magnesium glycinate is a different product and was disqualified from this ranking. Nutricost's powder is plain free-form glycine, which is exactly what you want for the 3 g pre-bed dose.

The pack prints Third Party Tested and GMP Compliant Facility seals, and the nutricost.com glycine powder page repeats Third-Party Tested and says the powder is manufactured in a GMP Compliant, FDA Registered Facility. No lab is named and no certificate of analysis is published. Nutricost's pages for some other products describe independent ISO-accredited laboratories, but neither this powder's pack nor its own page says so, so we do not credit it here. That is reasonable verification for a commodity amino acid, but it sits below NOW Foods' in-house analytical labs, below the per-batch, multi-stage program of the #3 bulk pick and below Thorne's third-party certification.

Because the two are level on score and Nutricost is ahead on the criteria that shape day-to-day use: dose accuracy (the measuring scoop is included in the tub) and purity and form. The gaps the other way: cost per gram is higher than the largest bulk bags, since Nutricost sells mainly in a 1 lb tub (about 150 servings) rather than a 1 kg bag, and the pack says only Third Party Tested without naming a lab. If the absolute lowest price or the strictest testing matters more to you than a measuring scoop in a tidy tub, buy the #3 pick instead.

1. [1] Bannai 2012 PMID 22529837 — The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. In healthy volunteers whose sleep was restricted for three nights, 3 g of glycine before bed significantly reduced subjective daytime fatigue and sleepiness and improved reaction-time performance versus placebo. The best-replicated glycine sleep finding — but a small study, and the authors are affiliated with a glycine manufacturer (noted for transparency).
2. [2] Kawai 2015 PMID 25533534 — The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Mechanistic study in rats: oral glycine promoted sleep and lowered core body temperature by acting on NMDA receptors in the suprachiasmatic nucleus (the master circadian clock), increasing skin blood flow and heat loss. Provides the leading biological explanation for glycine's sleep effect — but it is an animal study, so extrapolation to humans is indirect.
3. [3] Yamadera 2007 — Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. In volunteers with unsatisfactory sleep, 3 g of glycine before bed improved subjective sleep quality and, on polysomnography, shortened latency to sleep onset and to slow-wave sleep. The canonical human glycine-sleep study and the source of the 3 g dose — but small (~11 subjects) and published in a journal PubMed does not index, so no PMID exists. Cited honestly without a fabricated identifier.