What is HGH fragment 176-191?

What the 176-191 numbering means

Human growth hormone is a protein, and proteins are conventionally described by the position of each amino acid in the chain, counted from the N-terminus. A fragment name such as 176-191 states which positions of that parent chain the fragment reproduces: residue 176 at one end, residue 191 at the other, sixteen residues in total.

That convention is why the fragment is a fragment rather than a compound in its own right. The sequence is not invented; it is a defined slice of a larger molecule, and the numbering is the coordinate system that says which slice. A hexadecapeptide is the general term for a peptide of sixteen amino acids, which is the length this region produces.

The research record for AOD-9604 describes the compound as a synthetic hexadecapeptide corresponding to the C-terminal lipolytic domain of human growth hormone, written there as Tyr-hGH 177-191 and commonly referred to as hGH fragment 176-191. Both forms of the name appear in the same sentence of that record, which is the clearest statement that the numbering variants are labels for one sequence.

Is hgh frag 176 191 the same thing?

Yes. hgh frag 176 191 is a search shorthand and catalogue shorthand for the same sequence, with the word fragment abbreviated and the residue numbers retained. The abbreviation carries no additional chemical meaning: it does not denote a different salt form, a different length, or a different modification.

The same shorthand appears in the peer-reviewed literature. A 2026 critical review of peptide and peptide-analogue use in sport and bodybuilding lists synthetic fragments including Frag 176-191 among the agents it covers, alongside growth hormone secretagogues and growth hormone-releasing hormone analogues. That review treats Frag 176-191 as a named entry in a list of peptide classes, which is how the shorthand functions in the field.

A second 2026 narrative review, on approved and unapproved peptide therapies for musculoskeletal injuries and athletic performance, names AOD-9604 (anti-obesity drug 9604) in its list of compounds. The two reviews therefore use the two naming conventions for the same molecule, one descriptive and one catalogue-based, which is the practical reason a reader encounters both.

What the fragment is studied for

The research interest in this region comes from what it isolates. The catalogue entry states that the fragment isolates the lipolytic activity of full-length hGH whilst leaving IGF-1 and glucose regulation unaffected in preclinical models, making it a useful tool for studying fat metabolism independently of GH signalling.

The research record frames the same point as a recurring theme in the literature: separation of fat-metabolism effects from hGH-receptor-mediated and IGF-1-mediated effects. The record notes that preclinical work published between 1993 and 2001 characterised the fragment's effects on lipolysis, lipogenesis and fat oxidation in rodent models and reported that these effects occurred without measurable interaction with the hGH receptor or IGF-1 elevation.

The record also states the limits plainly. No randomised controlled efficacy trial of AOD-9604 has been published as a standalone peer-reviewed report; the human data available in the literature are a pooled safety and tolerability analysis, and body-composition outcomes have not been independently replicated in an indexed journal. Cartilage and osteoarthritis findings rest on a single small rabbit study with no human confirmation. Those findings, and the studies behind them, belong on the research record rather than being restated here.