What Is AOD-9604? The hGH Fragment 176-191 Peptide, Explained

The short version

So, what is AOD-9604? It is a lab-made peptide — a 16-amino-acid chain — copied from the tail end of human growth hormone (hGH). The name is short for "Anti-Obesity Drug 9604." Scientists found that one stretch of growth hormone, around residues 176–191, handled the hormone's fat-related effects. They rebuilt just that piece, added a tyrosine at the front, and kept an internal bridge that copies the parent hormone's loop. The goal: get the fat effect without the growth effect. Unlike full growth hormone, AOD-9604 does not plug into the growth-hormone receptor and does not raise IGF-1 (the growth signal). It is not growth hormone, not a compound that makes your body release its own growth hormone, not a steroid, and not a supplement. It is investigational — tested as an obesity drug, never approved. Below: where it came from and exactly what it is.

A piece of growth hormone, rebuilt on purpose

AOD-9604 is a synthetic hexadecapeptide — sixteen amino acids — modeled on the C-terminal end of human growth hormone (residues 177–191) with an N-terminal tyrosine added in place of the native phenylalanine ^[3]. Two cysteines form an internal disulfide bridge that mirrors the cystine loop of the parent hormone. Its reported sequence is Tyr-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe (YLRIVQCRSVEGSCGF), its molecular formula is C78H123N23O23S2, its molecular weight is 1815.1 Da, and its registry number is CAS 221231-10-3.

The origin story is straightforward: researchers at Monash University identified this tail region as the domain responsible for growth hormone's effect on fat metabolism ^[14]. Rebuilding just that region was an attempt to capture the fat effect while discarding the growth-promoting, IGF-1-raising arm of the full hormone. Metabolic studies confirmed the fat-metabolism activity sat in this synthetic C-terminal domain ^[3].

What AOD-9604 is not

Clearing up the common mix-ups matters as much as the definition.

• Not growth hormone. It is a fragment — one short piece — not the intact hormone. It cannot do what the whole hormone does.
• Not a secretagogue. It does not stimulate your body to release its own growth hormone. That is what CJC-1295, ipamorelin, and sermorelin do; AOD-9604 works differently and does not raise IGF-1 ^[3].
• Not a steroid. It is a peptide, structurally and mechanistically unrelated to anabolic steroids.
• Not a dietary supplement. Despite appearing near supplement searches, it has no approved supplement or drug status.
• Not an approved drug. It is investigational; the obesity program that developed it was discontinued after the pivotal trial failed ^[14].

Keeping these straight is the difference between an accurate read of the AOD-9604 research and the inflated "fat-loss peptide" version that circulates online.

Why it was interesting — and why it stalled

The appeal was real. A receptor-sparing fragment that mobilized fat in animals without raising IGF-1 or causing growth hormone's downsides would have been an elegant obesity drug. In obese mice, chronic treatment did reduce body weight and fat and raise beta-3 adrenergic receptor expression ^[1]. The human safety profile, across about 900 obese adults, was indistinguishable from placebo ^[5].

It stalled on efficacy. The pivotal Phase IIb obesity trial did not show statistically significant weight loss versus placebo, and development was discontinued around 2007 ^[14]. So the most accurate one-line answer to "what is AOD-9604" is this: a well-designed, receptor-sparing growth-hormone fragment with a strong animal mechanism, a clean human safety record, and an unproven human fat-loss effect.