Life Extension makes a perfectly good 1,000 mg glycine capsule, and the brand's QC reputation and published Certificate of Analysis give it real credibility. It is plain, vegetarian and non-GMO, the brand explicitly positions it for healthy sleep with straightforward labeling, and the 1 g cap keeps the studied 3 g dose to three capsules rather than six. The reason it sits at #7 rather than higher is pure economics, not quality. The bottle is only 100 capsules — about 33 nights at the 3 g sleep dose — so you reorder often, and the cost per gram lands above the near-identical Double Wood. If you are already a Life Extension loyalist who values the brand's COA and want a single-cap glycine with a strong QC story, it is a fine choice. For the same capsule format at a better price, Double Wood (#6) wins, and any powder beats it on value outright. Here is the full breakdown.
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Read the complete Glycine guide →Plain free-form glycine, vegetarian, non-GMO and gluten-free, no blend — the glycine the sleep studies used. Nothing disqualifying, and the brand's straightforward labeling is a plus. It scores level with the better capsules on purity; the ingredient itself is not the issue anywhere in this pick's ranking.
Life Extension's QC pedigree is among the most respected in the industry, and the brand makes a Certificate of Analysis available — real, credible verification for a commodity ingredient. It sits below Thorne's third-party certification and Pure Encapsulations' clinician-grade tier, but comfortably in the trustworthy range and ahead of budget capsules.
The 1 g cap is good — three caps make the 3 g dose, the same as Thorne and Double Wood. It scores lower than those two on this axis because the small 100-count bottle means you are constantly managing supply to keep hitting the dose; dose accuracy in practice is partly about having enough capsules on hand, and a 33-night bottle strains that.
Scored neutral, as capsules are throughout this ranking. A capsule avoids taste entirely — good for people who do not want to mix — but forfeits glycine's naturally sweet, pleasant-in-water quality, a genuine upside of the powders. A different trade, not a better or worse one.
The weak point. A 100-count bottle is only about 33 nights at the 3 g dose, and the cost per gram lands above the near-identical Double Wood, which ships 300 caps. You are paying a brand-and-COA premium for the same 1 g-cap format. Fair if you value the pedigree; not competitive on pure value.
“1,000 mg of plain glycine per capsule.”
The listing states 1,000 mg of glycine per capsule. This is the plain free-form glycine this ranking requires, and the 1 g cap is why the 3 g dose is three capsules rather than six — the claim holds as stated.
“Certificate of Analysis available from a QC-respected brand.”
Life Extension's QC reputation and availability of a Certificate of Analysis are well documented and central to the brand's positioning. Appropriate, credible verification for a commodity amino acid — the claim is accurate.
“Vegetarian, non-GMO, gluten-free.”
The product overview states a vegetarian, non-GMO, gluten-free formula, consistent with the plain-glycine capsule positioning. Accurate.
“Promotes healthy sleep at the glycine dose.”
Directionally supported by the human evidence on glycine — Yamadera 2007 and Bannai 2012 — but that evidence is moderate, drawn from a few small studies mostly from one lab, and describes glycine generally rather than this product. Life Extension's sleep positioning is a reasonable category claim, not a proven product-specific outcome.
There is nothing wrong with the glycine or the format here: plain 1,000 mg caps, so the studied 3 g dose is three capsules, from a brand with a genuinely strong QC reputation and a published COA. What drags it to #7 is arithmetic — the 100-count bottle covers only about 33 nights at the full dose, so you reorder roughly every month. For a supplement you take nightly and long-term, that reorder cadence and the higher resulting cost per gram matter, even though each individual capsule is excellent.
Life Extension and Double Wood are the same format — plain glycine, 1,000 mg per cap, three caps to the 3 g dose — so the tiebreaker is what you value. Double Wood ships 300 caps at a lower cost per gram; Life Extension ships 100 caps at a higher one, but brings a stronger QC pedigree and a published Certificate of Analysis. If that verification and brand trust are worth the premium to you, this is the pick; if price is what matters, Double Wood (#6) is the better buy in the identical format.
As with every capsule here, it is worth being plain: the glycine is chemically identical to the bulk powders, and a powder (#1 to #3) beats this on value outright — cheaper per gram and one 3 g scoop instead of three caps plus frequent reorders. Life Extension's appeal is the combination of capsule convenience and a trusted QC brand with a COA; it is not, and does not try to be, the cost-efficiency pick.
The QC-brand capsule still delivers just glycine: a gentle aid backed by moderate evidence from a few small studies. About 3 g before bed improved subjective sleep quality and shortened polysomnographic sleep latency (Yamadera 2007), and most reliably reduced next-day fatigue after a short night (Bannai 2012). Take three caps nightly for one to two weeks before judging, and stack it with a cool room and consistent sleep timing. It is a trustworthy way to take glycine for sleep — it is still a small, well-tolerated edge, not a cure.
Life Extension Glycine is a solid, trustworthy 1,000 mg single-cap glycine, and the brand's QC reputation and published Certificate of Analysis give it real credibility. It is plain, vegetarian and non-GMO, positioned for healthy sleep with straightforward labeling, and the 1 g cap keeps the studied 3 g dose to three capsules. It sits at #7 purely on economics. The bottle is only 100 capsules — about 33 nights at the 3 g dose — so you reorder often, and the cost per gram lands above the near-identical Double Wood. If you are a Life Extension loyalist who values the brand's COA, it is a fine choice. But for the same capsule format at a better price, Double Wood (#6) wins, and any powder (#1 to #3) beats it on value outright. As with every pick, take 3 g (three caps), 30 to 60 minutes before bed, give it one to two weeks, and stack it with good sleep timing and a cool room.
Check Life Extension · plain glycine capsules · 1,000 mg each · 100 caps on AmazonThe same 1 g-cap format at a better price — 300 caps (about 100 nights), third-party tested, lowest capsule cost per gram. The value pick over Life Extension unless you specifically want its COA.
See it on the list →The best-tested capsule, third-party certified, also 1 g per cap. Choose it if maximum verification pedigree matters more than price.
See it on the list →The overall winner — plain glycine at the lowest cost per gram with a 3 g scoop. Buy it if value and one pre-portioned dose matter more than capsule convenience.
See it on the list →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).
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.
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.
