At a glance

What is Fragment 176-191?

Fragment 176-191 is the C-terminal (tail) fragment of human growth hormone, sold on the "research peptide" market for fat loss. It is closely related to AOD-9604, which is this fragment with an added stabilizing amino acid; the two are often conflated and sold interchangeably, but AOD-9604 is the engineered, better-studied version. Much of what vendors label "176-191" is pharmacologically the same fat-metabolism concept.

How does it work?

The proposed theory is that the fat-related activity of growth hormone is concentrated in this tail fragment, so the fragment alone might reduce fat storage without the hormone's growth or glucose effects. In rat studies¹, the fragment was shown to carry the anti-fat-storage activity of the parent hormone, localizing that function to the C-terminal region. The tested peptide was hGH 177-191, a close relative of this fragment, and it showed no significant lipolytic effect in rat fat pads. These are animal and cell findings. This describes the proposed mechanism, separate from proven outcomes.

The more detailed mechanism data belong to AOD-9604, the modified version, and not to the bare fragment. In obese Zucker rats, AOD-9604 cut weight gain over 50% in 19 days² and raised lipolytic activity in adipose tissue, without the insulin-sensitivity harm seen with intact growth hormone. In obese mice, AOD-9604 increased fat oxidation and plasma glycerol³, a marker of fat breakdown, and it did not compete for the growth hormone receptor or drive cell proliferation.

Is it FDA-approved?

No. Fragment 176-191 is not approved by the FDA; it is a "research chemical" with no approved drug or recognized compounding status, sold through gray-market channels. AOD-9604, the modified version, was developed by Metabolic Pharmaceuticals as an obesity drug, but its development was terminated in 2007⁴ after it failed to show efficacy. In sport, growth hormone fragments including "hGH 176-191" are prohibited at all times under the WADA list.

What does the research show?

The evidence is preclinical. Animal work localized the anti-lipogenic activity of growth hormone to this C-terminal fragment, and the closest human data belong to its modified version, AOD-9604, whose obesity trials failed to beat placebo. There are no controlled human trials of the bare fragment for fat loss, so its marketed benefit is unproven.

The human data belong to AOD-9604, as reported in a review of obesity drug development.

Those results do not describe the bare fragment, which has not been tested in controlled human trials.

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