AOD-9604 is a 16-residue synthetic peptide corresponding to the C-terminal region of human growth hormone: hGH residues 177–191 with a tyrosine appended at the N-terminus. That makes it equivalent to hGH(176–191) with the native phenylalanine at position 176 replaced by tyrosine. The two cysteines — hGH Cys182 and Cys189, occupying positions 7 and 14 of the fragment — form a disulfide bridge closing the peptide into a ring, as they do in the parent hormone.

The design rests on work at Monash University in the 1990s which localised the lipolytic activity of full-length hGH to this C-terminal region, separately from the growth-promoting and insulin-antagonising activities that map elsewhere in the protein. AOD-9604 is not a growth hormone secretagogue: it does not act at the GHRH or ghrelin receptors and does not stimulate release of endogenous growth hormone. It has been studied in adipocyte preparations, in rodent models of obesity, and more recently in models of cartilage and joint tissue. WADA lists growth hormone fragments, naming AOD-9604 and hGH 176-191 explicitly, under section S2 of the Prohibited List.

Development as a human obesity therapeutic was discontinued after the largest company-sponsored clinical study did not meet its primary endpoint, and the compound has never been approved as a medicine in any jurisdiction. It is also frequently sold interchangeably with 'HGH Fragment 176-191', which is a genuinely different peptide — the same disulfide-bridged core, but phenylalanine rather than tyrosine at the N-terminus — carrying a different registry number and mass. The two are not substitutes for one another.