HGH-191AA
Recombinant human growth hormone, full 191-amino-acid sequence.
Growth hormone axis · 8 min read · updated 13 Aug 2026
Research use only. The ranges below are what published studies and community protocols report. They are reference material for laboratory research, not medical advice or a recommendation for human or veterinary use.
The compound
HGH-191AA
View- Type
- Somatropin (Recombinant)
- CAS
- 12629-01-5
- Formula
- C₉₉₀H₁₅₂₉N₂₆₃O₂₉₉S₇
- Mass
- ~22,125 Da
At a glance
- Class
- Recombinant somatropin
- Length
- 191 amino acids — identical to pituitary hGH
- Molecular weight
- ~22,125 Da
- CAS
- 12629-01-5
- Unit conversion
- 1 mg ≈ 3 IU
- Plasma half-life
- ~3–4 h subcutaneous; biological effect far longer via IGF-1
- Vial sizes stocked
- 12 IU (4 mg), 24 IU (8 mg)
The "191AA" in the name is the whole point. Human growth hormone is a 191-residue protein with two disulfide bridges. Early recombinant production in E. coli left an extra N-terminal methionine, giving a 192-amino-acid variant that was more immunogenic. Modern material is the true 191-residue sequence, correctly folded and identical to what the pituitary secretes.
GH does comparatively little on its own. It binds a dimeric GH receptor, activating JAK2 and STAT5, and the dominant downstream event is hepatic IGF-1 synthesis. Most of the anabolic and growth-promoting effects attributed to GH are IGF-1-mediated. A handful of effects are direct — lipolysis in adipose tissue and the antagonism of insulin action in muscle and liver among them — and those direct effects are why GH is not simply an IGF-1 delivery mechanism.
Endogenous secretion is pulsatile, with the largest pulses during early slow-wave sleep. Exogenous administration flattens that pattern into a single broad peak. Whether pulsatility matters for a given endpoint is one of the open questions the research literature keeps returning to.
Mechanism in detail
- Liver: GH receptor activation drives IGF-1 and IGFBP-3 transcription. Serum IGF-1 is the standard biomarker of GH exposure precisely because it integrates the pulses into a stable signal.
- Adipose: direct lipolytic action via hormone-sensitive lipase, with a preference for visceral depots. This is the fastest-appearing effect and the one least dependent on IGF-1.
- Muscle and connective tissue: IGF-1-driven protein synthesis, and increased collagen turnover in tendon and skin.
- Glucose handling: GH is frankly diabetogenic at higher exposures. It induces hepatic glucose output and peripheral insulin resistance, and this is dose-dependent and reversible.
- Fluid balance: sodium and water retention via the renin–angiotensin system produces the puffiness, joint stiffness and carpal-tunnel symptoms that dominate the reported adverse-event profile.
Units, milligrams and the arithmetic that goes wrong
GH is sold in international units but reconstituted by volume, and the conversion trips people constantly. The standard factor is 3 IU per milligram. A 12 IU vial therefore contains 4 mg of protein; a 24 IU vial contains 8 mg.
Because vials are labelled in IU, dosing is nearly always expressed in IU too. Keep one unit system for the entire protocol — mixing "2 IU" and "0.67 mg" in the same notes is how doubling errors happen.
Timing
Two timing conventions dominate reported protocols. The first administers in the evening, on the theory of reinforcing the natural nocturnal pulse. The second administers in the morning, on the theory that an evening dose suppresses the endogenous pulse and disturbs sleep architecture. Neither has decisively won on evidence.
What is better established is the interaction with carbohydrate: an insulin spike blunts the GH response and, conversely, GH opposes insulin action. Reported protocols therefore administer away from large carbohydrate loads, typically with a 1–2 hour gap.
Splitting a daily amount into two administrations produces a less flattened profile and is common at higher totals.
Storage
- Lyophilised: 2–8 °C. Genuine GH tolerates brief room-temperature transit but should not be stored warm.
- Reconstituted: 2–8 °C, and used within about 14–21 days — a shorter window than the small peptides.
- Never freeze reconstituted GH. Freezing is the single most reliable way to destroy it.
- Protect from light throughout.
Cautions
- Insulin resistance rises with dose and duration. This is the most consequential effect of sustained GH exposure and it is frequently underestimated.
- Carpal tunnel syndrome, arthralgia and oedema are the classic dose-limiting effects.
- GH promotes growth of tissue generally. Its interaction with existing neoplastic processes is the reason active malignancy is an absolute exclusion in the clinical literature.
- Effects on thyroid conversion and cortisol metabolism mean thyroid panels shift during GH exposure and should be interpreted in that light.
References & credit
- 1Møller N, Jørgensen JOL — Endocrine Reviews 2009 — Effects of growth hormone on glucose, lipid and protein metabolism in humans.
- 2Molitch ME et al., J Clin Endocrinol Metab 2011 — Endocrine Society guidance on adult GH deficiency — the clinical dose reference above.
- 3Liu H et al., Annals of Internal Medicine 2007 — Systematic review of GH in healthy elderly subjects — body composition versus functional endpoints.
This article was written in-house. Where a dose range reflects community practice rather than a published trial, the community references we consulted are credited above and the article says which is which.