HGH 191aa is the single most-ordered research compound through this site — 12 of the 46 vendor orders we have tracked, more than any other peptide we cover, and every one of them went to ZestyRat Research. Here is what the 191-amino-acid recombinant protein actually is, why its purity spec reads differently from a synthetic peptide, and the verified bulk price ladder that makes ten vials cost less per unit than one.
HGH 191aa is recombinant human growth hormone — a 191-amino-acid single-chain polypeptide registered under CAS 12629-01-5, with the molecular formula C990H1528N262O300S7 and a molecular weight of 22,124 g/mol. The "191aa" in the name is doing real work: it signals the full-length sequence, identical in length to the growth hormone the human pituitary produces, as distinct from truncated or fragment forms such as AOD-9604 (a 176–191 fragment).
It is produced by recombinant expression rather than extracted from tissue, and supplied as a lyophilized powder for laboratory reconstitution. In research settings it functions as a reference standard for growth hormone receptor work — the known quantity you calibrate an assay against.
This is the single most common point of confusion in the growth-hormone category, and it changes how everything else is read. HGH 191aa is growth hormone. The compounds it sits next to on most vendor menus are not — they are secretagogues, molecules that signal the pituitary to release the body's own growth hormone.
Put simply: the secretagogues work one step upstream, amplifying a natural pulsatile rhythm. HGH 191aa skips the pituitary entirely. That is why the two groups are studied with different endpoints and why their purity specifications are not comparable. Compare the whole class on the growth-hormone peptide category page.
ZestyRat publishes ≥96% HPLC purity on its HGH 191aa, and at a glance that looks weaker than the 99%+ figures posted on short synthetic peptides. It is not, and the reason is analytical rather than promotional.
A 191-residue recombinant protein is a fundamentally harder target than a 5 mg synthetic like BPC-157. Longer chains carry more opportunities for deamidation, oxidation and conformational variants; recombinant expression introduces host-cell considerations that solid-phase synthesis does not. A 96% figure on a 22 kDa protein and a 99% figure on a 15-residue peptide are not the same measurement, and treating them as directly comparable is one of the easier ways to misread a vendor menu. Judge a protein against protein norms.
Storage carries the same asymmetry. As lyophilized powder the material is specified for -20°C, protected from light and moisture. Recombinant proteins are more sensitive to freeze-thaw cycling and to heat in transit than small synthetics — which makes shipping practice a genuine quality variable here, not a footnote.
ZestyRat runs a quantity discount that stacks with our code, and almost nobody works the arithmetic out before checkout. The bulk tiers are 10% off at 5–9 units and 20% off at 10+ units, and SHAUN10 applies on top of the discounted price. Prices verified directly on the ZestyRat product page.
| Quantity | 24iu list | 24iu + bulk | + SHAUN10 | 10iu final |
|---|---|---|---|---|
| 1–4 units | $49.99 | $49.99 | $44.99 | $35.99 |
| 5–9 units 10% bulk | $49.99 | $44.99 | $40.49 | $32.39 |
| 10+ units ★ 20% bulk | $49.99 | $39.99 | $35.99 | $28.79 |
At ten units of the 24iu the effective unit price falls from $49.99 to $35.99 — a 28% total reduction, and the 10iu size lands at $28.79. That stacked ladder is the reason bulk orders are the norm rather than the exception in this category: the tenth vial costs less than three-quarters of the first.
Buy directly from vetted research-peptide vendors below. Each product ships from the vendor and is sold strictly for laboratory and research use — not for human consumption. Links are affiliate links, disclosed per FTC guidelines; you pay the same price (and often less with our codes).
We rank vendors, we do not run one, so the useful thing we can offer here is not an opinion — it is what our readers actually did. Across every order we have been able to track through this site, the pattern on this compound is not close.
Read the full ZestyRat Research review › · Compare every vendor side by side
HGH 191aa is recombinant human growth hormone — a 191-amino-acid single-chain polypeptide (CAS 12629-01-5, MW 22,124 g/mol) produced by recombinant expression rather than extraction. The 191aa designation signals the full-length sequence, matching pituitary-derived growth hormone. It is sold as a laboratory reference standard for growth hormone receptor research, not for human use.
HGH 191aa is growth hormone itself. Sermorelin, CJC-1295, tesamorelin and ipamorelin are secretagogues — they signal the pituitary to release the body's own growth hormone. That is the fundamental distinction: HGH 191aa supplies the hormone directly, while the secretagogues act one step upstream on the GH axis.
ZestyRat publishes ≥96% HPLC. Recombinant proteins of this size are typically specified lower than short synthetic peptides — a 191-residue protein is a far harder analytical target than a 5mg synthetic like BPC-157, so a 96% figure on a protein is not comparable to 99% on a short peptide. Judge it against protein norms.
ZestyRat applies a quantity ladder: 5–9 units take 10% off and 10+ units take 20% off, and the SHAUN10 code stacks on top of the bulk price. On the 24iu that moves the unit price from $49.99 to $35.99 at ten units — a 28% total reduction. See the full ladder above.
As lyophilized powder, at -20°C, protected from light and moisture. Recombinant proteins are more sensitive to freeze-thaw cycling and to heat during transit than small synthetic peptides, which makes shipping practice a genuine quality variable rather than a footnote.
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Specifications and pricing verified September 2026. By the Peptides Uncaged Research Team.
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