A research overview of the HGH Fragment 176-191 peptide: the tyrosine-modified hGH C-terminal sequence, the Monash rodent lipolysis studies, the AOD-9604 human trials, and how mature the evidence is.
HGH Fragment 176-191 is a sixteen-residue synthetic peptide modelled on the C-terminal tail of human growth hormone. It exists because of one hypothesis: that growth hormone's fat-mobilising activity sits in a short stretch at the end of the molecule and can be separated from the receptor-driven effects — IGF-1 elevation, impaired glucose tolerance, tissue growth — that make the full hormone unsuitable as a metabolic agent. This overview covers the sequence and its confusing numbering, the rodent work that built the hypothesis, what happened when the same molecule reached human trials under the name AOD-9604, and how mature the evidence actually is.
It sits beside the HGH Fragment 176-191 compound profile, the research dosing notes and the side-effect review.
Native human growth hormone is a 191-amino-acid protein that ends in the sequence Phe-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe (residues 176–191), with a disulfide bond between Cys182 and Cys189. The research peptide sold as "HGH Fragment 176-191" is Tyr-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe: residues 177–191 of the hormone with a tyrosine at the N-terminus, in the position where native hGH holds a phenylalanine. Molecular weight is approximately 1,815 Da, and the internal disulfide is retained.
That single tyrosine explains the two naming conventions. Describe it as "hGH 177–191 plus an added tyrosine" and you have the developer's description of AOD-9604; describe it by the span of positions it occupies and you have "176-191". They are the same molecule, a point covered in detail in AOD-9604 vs HGH Fragment 176-191. Differences between vials on the market are questions of synthesis quality, purity and counter-ion content — the subjects of reading a peptide COA — not of molecular identity.
The fragment programme came out of Frank Ng's laboratory at Monash University in Melbourne. Wu and Ng, in Biochemistry and Molecular Biology International (1993), reported that a synthetic peptide corresponding to hGH 177–191 reduced lipogenesis in rodent adipose tissue. Ng and colleagues then characterised the tyrosine-modified version in Hormone Research (2000), reporting lipolytic and anti-lipogenic effects in obese rodents without the blood-glucose disturbance produced by intact growth hormone.
Two papers from the same group in 2001 carried most of the mechanistic weight. Heffernan and colleagues in the International Journal of Obesity reported that chronic treatment of obese mice with either hGH or the modified fragment increased fat oxidation and reduced body weight. The companion paper in Endocrinology examined the β3-adrenergic receptor, the dominant lipolytic receptor in rodent fat. In β3-receptor knockout mice, chronic treatment with hGH or the fragment no longer produced the weight change and lipolytic increase seen in wild-type animals — yet in an acute experiment the fragment still raised energy expenditure and fat oxidation in the knockouts. The authors' conclusion was nuanced: the lipolytic action is not mediated directly through the β3 receptor, but both compounds increased β3-receptor expression, which may contribute to enhanced lipolytic sensitivity over time.
What that literature does not provide is a defined molecular target. The fragment does not bind the growth hormone receptor with meaningful affinity, and no specific receptor for it has been identified. It also rests on a caveat that recurs throughout metabolic pharmacology: β3-adrenergic biology differs substantially between rodents and humans, and rodent lipolysis findings have a long record of translating poorly.
The Australian company Metabolic Pharmaceuticals licensed the programme and developed the molecule as AOD-9604 — administered orally throughout its clinical development. A 12-week Phase 2a trial of roughly 300 subjects with obesity, announced by the company in 2004, reported about 2.6 kg of weight loss on 1 mg daily against about 0.8 kg on placebo. The confirmatory Phase 2b study enrolled 536 subjects for 24 weeks and did not separate from placebo on its primary weight-loss endpoint. Development for obesity was terminated in 2007, and neither trial's primary results were published as a full peer-reviewed report; the figures come from company disclosures and later reviews.
The safety data are better documented. Stier, Vos and Kenley, in the Journal of Endocrinology and Metabolism (2013), pooled six randomised, placebo-controlled trials and reported tolerability comparable to placebo, no change in serum IGF-1, no adverse effect on glucose tolerance, and no anti-drug antibodies. The separation-from-hGH hypothesis, in other words, held on the safety side; efficacy was what failed. The full clinical history is in the AOD-9604 research overview.
| Evidence layer | What exists | Limitation |
|---|---|---|
| In vitro / ex vivo | Anti-lipogenic and lipolytic activity in rodent adipose tissue | No identified receptor |
| Rodent in vivo | Reduced body weight and increased fat oxidation in obese mice (2000–2001) | Intraperitoneal or oral dosing; largely one research group |
| Human efficacy | Positive oral Phase 2a; negative oral Phase 2b (536 subjects) | No full peer-reviewed primary report |
| Human safety | Pooled six-trial analysis (2013) | Oral route only |
| Injectable fragment in humans | None published | — |
Every controlled human dataset used oral tablets. Research material such as the HGH FRAG 176-191 5MG vial is supplied lyophilised for reconstitution, a different route with a different exposure profile, and no human pharmacokinetic or efficacy study of the injectable fragment has been published. Claims about its potency in people are not derived from trial data.
Set beside the incretin class — semaglutide, tirzepatide, retatrutide — the gap in evidence weight is large: those compounds have published late-stage trial programmes that met their endpoints (see GLP-1 receptor agonists compared). HGH Fragment 176-191's research interest is narrower and mechanistic: a GH-derived peptide that appears to engage lipid metabolism without raising IGF-1, with a reasonably characterised oral safety profile and a negative efficacy trial behind it.
Regulatory status is also narrow. The compound has no drug approval from Health Canada, the FDA or any other regulator, and is sold in Canada for research use only. Its status for U.S. compounding has shifted more than once and should be checked against current FDA listings rather than assumed. WADA names both hGH fragment 176-191 and AOD-9604 under S2, so it is prohibited in sport at all times.
Is HGH Fragment 176-191 the same as AOD-9604? Yes. Both names describe the same sixteen-residue peptide — hGH 177–191 with an N-terminal tyrosine. "AOD-9604" is the developer's code; "176-191" describes the positions the sequence spans.
Does HGH Fragment 176-191 raise IGF-1? Rodent studies and a pooled analysis of six human oral trials reported no rise in IGF-1 and no adverse effect on glucose tolerance. That separation from intact growth hormone was the central design goal.
Did it work for weight loss in human trials? A 12-week oral Phase 2a trial reported a modest advantage over placebo; the larger 24-week Phase 2b trial in 536 subjects did not meet its primary endpoint, and development stopped in 2007.
How does it act on fat tissue? Rodent work points to increased lipolysis and reduced lipogenesis in adipose tissue, with increased β3-adrenergic receptor expression as one possible contributor. No specific receptor has been identified, and the mechanism has not been confirmed in humans.
Is this medical advice? No. HGH Fragment 176-191 is research-grade material for laboratory research only, not for human or veterinary consumption. This page summarises published literature and is not a treatment or dosing recommendation.
