HGH 191AA is recombinant human growth hormone: the same 191-amino-acid chain the pituitary makes, only produced by bacteria in a manufacturing plant. Unlike peptides that ask the pituitary for a burst of hormone, HGH acts directly and bypasses the whole regulatory loop. It is the only compound in this group that has been a licensed medicine for decades, so there is plenty of evidence — and in several places it says something different from the marketing: in healthy people growth hormone shifts body composition by about two kilograms in each direction, does not improve strength, and clearly raises the number of adverse events. Below we set out what was actually measured and where the knowledge ends.
What HGH 191AA is
Growth hormone (GH; as a medicine it is called somatropin) is a protein secreted by the pituitary, a bean-sized gland at the base of the brain. The human molecule has 191 amino acids, hence the commercial label "191AA": it is meant to signal that the vial holds the full-length human sequence rather than a truncated fragment. The pituitary does not release GH evenly but in pulses, strongest during sleep.
How it works — pituitary, liver and IGF-1
Growth hormone docks onto its receptor (a "switch" on the cell surface) and triggers a chain of signals inside the cell. Some effects are direct: in fat tissue GH steps up the breakdown of fat and raises free fatty acids in the blood. Others are indirect: GH prompts the liver to make IGF-1 (insulin-like growth factor 1), and it is IGF-1 that carries out most of the "building" action. Hence the phrase GH-IGF-1 axis. The review by Moller and Jorgensen describes the main cost of this cascade: GH is a counterregulatory hormone to insulin and blunts insulin's action in the liver and in peripheral tissue, and the mechanism is the increased flux of free fatty acids competing with glucose. That is why acromegaly (a disease of GH excess) brings insulin resistance, and why insulin sensitivity temporarily worsens in GH-deficient adults when treatment starts.
Structure and origin — where "191AA" comes from
Until 1985 growth hormone was extracted from pituitary glands taken from cadavers. The review by Ranke and Wit divides the history of GH into three eras: basic research in the first half of the twentieth century, the pituitary-derived era (1958-1985), and the recombinant-technology era from 1985 onwards, which continues today. Recombinant preparations are grown in bacteria or cells from the human gene, so they contain no material harvested from people. The same review notes that the indications have steadily widened beyond classic growth-hormone deficiency, and that safety concerns still accompany this therapy.
Human data — what the systematic reviews say
The strongest body of evidence in healthy people comes from two systematic reviews in the Annals of Internal Medicine by Liu's group at Stanford University. The first pooled 31 papers on 18 study populations — 220 people who received GH (107 person-years), averaging 69 years of age and treated for 27 weeks on average. The result: fat mass fell by 2.1 kg, lean body mass rose by 2.1 kg, and body weight did not change (+0.1 kg). Bone density was unchanged. People given GH were significantly more likely to have soft-tissue oedema, joint pain, carpal tunnel syndrome and gynaecomastia (breast-tissue growth in men), and "somewhat more likely" to develop diabetes or impaired fasting glucose. The authors' conclusion: growth hormone cannot be recommended as an antiaging therapy.
The second review covered young, trained people: 44 papers, 303 participants on GH, 13.3 person-years. Lean body mass rose by 2.1 kg — the same figure as in older adults — but strength and exercise capacity did not improve, and lactate during exercise was higher in two of the three studies that measured it. Treated participants more often reported oedema and fatigue. The verdict: claims that growth hormone enhances physical performance are not supported by the literature.
Collagen instead of myofibrils — the 2010 trial
The explanation of that gap — mass rises, strength does not — came from Doessing's group in Copenhagen. Healthy young volunteers received recombinant GH at a daily dose of 33-50 micrograms per kilogram of body weight for two weeks, while the researchers measured the rate at which two kinds of protein were being made: collagen (the scaffolding of connective tissue) and myofibrils (the fibres that generate contractile force). Collagen synthesis in tendon rose 1.3-fold and collagen I gene expression in tendon 3.9-fold; in muscle, gene expression rose 2.3-fold and collagen protein synthesis 5.8-fold — but this last result did not cross the threshold of significance (p = 0.06), so it is a signal, not a certainty. Myofibrillar protein synthesis did not change at all. The authors concluded that in adults GH matters more for strengthening connective tissue than for the growth of muscle cells.
Athletes — a large randomised trial
The best-designed trial in athletes was run by Meinhardt's group in Sydney and funded by the World Anti-Doping Agency. It enrolled 96 recreationally trained people (63 men, 33 women) with a mean age of 27.9 years; for eight weeks they received placebo or GH at a daily dose of 2 mg, with men additionally given testosterone or both agents together. GH cut fat mass and raised lean body mass — but through an increase in extracellular water; body cell mass rose only in men combining GH with testosterone. Of the four performance measures assessed (endurance, strength, power, sprint), one improved: sprint capacity, by 3.9 % across the whole group and by 8.3 % in men on both agents. Six weeks after stopping, the advantage had gone.
Safety and the limits of the evidence
The largest data on long-term outcomes come from the European SAGhE programme, which followed children treated with GH from 1984 onwards. The mortality analysis covered 24,232 patients and more than 400,000 person-years: in people with isolated GH deficiency or idiopathic short stature, all-cause mortality was not raised (ratio 1.1), whereas it rose in groups with a serious underlying disease — and it was not related to dose. The parallel cancer analysis in 23,984 patients found no general carcinogenic effect but left questions open: among people treated after a previous cancer, cancer mortality rose with daily dose, and among those with no previous cancer, bone and bladder cancers were more common.
Diabetes comes with concrete numbers. In an analysis of 23,333 children treated with GH, the incidence of type 1 diabetes matched expectation, but the incidence of type 2 diabetes was 34.4 cases per 100,000 years of treatment — six times the rate in untreated children — and it did not resolve after treatment stopped. The authors read this as an acceleration of the disease in predisposed individuals. In healthy adults the signal is weaker ("somewhat more likely" in the Liu review). The third issue is the body's own output: GH suppresses itself through a feedback loop. In healthy men, giving the 20 kDa isoform markedly suppressed secretion of the body's own, dominant 22 kDa isoform. A different isoform from the 191AA product was studied, so this is evidence that the mechanism exists, not a measurement of its size. We deliberately give no methods of use and no doses.
What could not be established
Two claims from the internet have no backing in the literature we checked. The first: a "six-fold rise in collagen synthesis in tendon and skin within 14 days" — in Doessing's trial the 5.8-fold figure applied to collagen in muscle (and was not significant), tendon synthesis rose 1.3-fold, and skin was not studied. The second: a threshold of "about 2 IU, above which adverse events climb steeply with no added benefit" — we found no such relationship in any paper; SAGhE points to mortality being unrelated to dose, and the Liu reviews did not analyse thresholds. Dose matters, but this particular number has no source.
The wider context — the whole GH axis
HGH is the reference point for the entire family of "growth hormone" peptides. Some act higher up and merely coax the pituitary into working — GHRH analogues such as tesamorelin and sermorelin, and ghrelin mimetics such as ipamorelin. Others sit lower down: IGF-1 LR3 is the end effector of the same pathway, while fragment 176-191 is a piece cut out of the GH molecule. Secretagogues preserve the natural feedback loops and pulsatility; injected growth hormone overrides them.
Summary
HGH 191AA is full-length recombinant growth hormone — the only substance in this group with a genuine drug record. In healthy people the effect is predictable and modest: about 2 kg less fat and 2 kg more lean mass (partly water), no gain in strength or endurance, but more oedema, joint pain, carpal tunnel syndrome and gynaecomastia. The regenerative mechanism looks real, but it concerns connective tissue rather than muscle fibres. The best-documented metabolic risk is type 2 diabetes — six times more common in treated children — because GH is by nature an insulin antagonist. State of the evidence: strong and well measured — and pointing to conclusions opposite to the advertising.
Sources
- Liu H, Bravata DM, Olkin I, et al. Systematic review: the safety and efficacy of growth hormone in the healthy elderly. Annals of Internal Medicine. 2007;146(2):104-115. PMID: 17227934. DOI: 10.7326/0003-4819-146-2-200701160-00005. pubmed.ncbi.nlm.nih.gov/17227934
- Liu H, Bravata DM, Olkin I, et al. Systematic review: the effects of growth hormone on athletic performance. Annals of Internal Medicine. 2008;148(10):747-758. PMID: 18347346. DOI: 10.7326/0003-4819-148-10-200805200-00215. pubmed.ncbi.nlm.nih.gov/18347346
- Meinhardt U, Nelson AE, Hansen JL, et al. The effects of growth hormone on body composition and physical performance in recreational athletes: a randomized trial. Annals of Internal Medicine. 2010;152(9):568-577. PMID: 20439575. DOI: 10.7326/0003-4819-152-9-201005040-00007. pubmed.ncbi.nlm.nih.gov/20439575
- Doessing S, Heinemeier KM, Holm L, et al. Growth hormone stimulates the collagen synthesis in human tendon and skeletal muscle without affecting myofibrillar protein synthesis. The Journal of Physiology. 2010;588(2):341-351. PMID: 19933753. DOI: 10.1113/jphysiol.2009.179325. pubmed.ncbi.nlm.nih.gov/19933753
- Swerdlow AJ, Cooke R, Beckers D, et al. Cancer Risks in Patients Treated With Growth Hormone in Childhood: The SAGhE European Cohort Study. The Journal of Clinical Endocrinology and Metabolism. 2017;102(5):1661-1672. PMID: 28187225. DOI: 10.1210/jc.2016-2046. pubmed.ncbi.nlm.nih.gov/28187225
- Sävendahl L, Cooke R, Tidblad A, et al. Long-term mortality after childhood growth hormone treatment: the SAGhE cohort study. The Lancet Diabetes & Endocrinology. 2020;8(8):683-692. PMID: 32707116. DOI: 10.1016/S2213-8587(20)30163-7. pubmed.ncbi.nlm.nih.gov/32707116
- Cutfield WS, Wilton P, Bennmarker H, et al. Incidence of diabetes mellitus and impaired glucose tolerance in children and adolescents receiving growth-hormone treatment. The Lancet. 2000;355(9204):610-613. PMID: 10696981. DOI: 10.1016/S0140-6736(99)04055-6. pubmed.ncbi.nlm.nih.gov/10696981
- Hashimoto Y, Kamioka T, Hosaka M, et al. Exogenous 20K growth hormone (GH) suppresses endogenous 22K GH secretion in normal men. The Journal of Clinical Endocrinology and Metabolism. 2000;85(2):601-606. PMID: 10690862. DOI: 10.1210/jcem.85.2.6377. pubmed.ncbi.nlm.nih.gov/10690862
- Møller N, Jørgensen JO. Effects of growth hormone on glucose, lipid, and protein metabolism in human subjects. Endocrine Reviews. 2009;30(2):152-177. PMID: 19240267. DOI: 10.1210/er.2008-0027. pubmed.ncbi.nlm.nih.gov/19240267
- Ranke MB, Wit JM. Growth hormone - past, present and future. Nature Reviews Endocrinology. 2018;14(5):285-300. PMID: 29546874. DOI: 10.1038/nrendo.2018.22. pubmed.ncbi.nlm.nih.gov/29546874
For in-vitro laboratory research only. It is not a human medicine and is not for treatment.