A 16-amino-acid piece of the tail of human growth hormone, tested as a fat-loss drug. Its human trials found no significant weight loss.
Also called hGH 176-191, Frag 176-191, Growth hormone fragment 176-191, Tyr-hGH 177-191, AOD-9604 (same sequence in most products)
Growth hormone is a 191-amino-acid protein. In the early 1990s researchers at Monash University found that a short piece from its far end, residues 177 to 191, kept growth hormone's fat-burning effect in rodent fat tissue without its effects on growth or blood sugar. Adding a tyrosine to the front of that piece produced AOD-9604. Products sold as HGH Fragment 176-191 usually carry the same 16-residue sequence as AOD-9604, so for practical purposes the two names describe one compound.
In obese mice and rats the fragment cut weight gain, raised fat burning and did not cause the high blood sugar that full growth hormone does. It does not bind the growth hormone receptor and does not raise IGF-1. Those animal results led to six placebo-controlled human trials in about 900 people, run by the developer, Metabolic Pharmaceuticals.
The human trials showed the drug was well tolerated, with side effects similar to placebo, no rise in IGF-1 and no harm to glucose tolerance. They did not show it works. The largest, a 24-week trial in 502 obese adults, did not produce significant weight loss compared with placebo at 12 or 24 weeks, and the developer ended the obesity program in February 2007. Those trials used oral tablets and IV infusions. The daily under-the-skin injections people use today have never been tested in a published trial.
What it binds to, and what happens inside the body after that, step by step.
Animal and cell work suggests the C-terminal piece of growth hormone acts on fat cells to raise fat breakdown and lower fat storage. It does not bind or activate the growth hormone receptor, does not raise IGF-1, and in mice did not raise blood sugar. Its actual receptor is unknown; it raised beta-3 adrenergic receptor expression in obese mice. In mice lacking that receptor, two weeks of dosing no longer cut weight, but a single dose still raised fat burning.
Human results and animal results are kept apart below. A result in rats tells you a mechanism is plausible. It does not tell you what happens in a person.
Grade B reflects that randomized human trials exist, not that they were positive. Six company-run placebo-controlled trials of the AOD-9604 sequence in about 900 people showed good tolerability and no effect on IGF-1 or blood sugar, but the decisive 24-week trial found no significant weight loss and was never published in a journal. Those trials used oral and IV dosing; the injected product sold today has no human data. The fat-burning effects are shown in rodents and in fat tissue samples only.
No human studies are among the key studies for HGH Fragment 176-191. Everything known comes from animals or cells.
Obese (ob/ob) and lean mice, 14 days
AOD-9604 reduced weight gain and raised fat burning like growth hormone, but unlike growth hormone it did not raise blood sugar or bind the growth hormone receptor.
Read the studyObese Zucker rats, 19 days of oral dosing
Weight gain was cut by more than half (15.8 g vs 35.6 g) with no loss of insulin sensitivity.
Read the studyObese mice for 30 days, plus fat tissue from obese rodents and humans
Treated mice gained less weight from day 16 on with no change in food intake; the peptide raised fat breakdown in human fat tissue samples in the lab.
Read the studyObese mice and beta-3 adrenergic receptor knockout mice
The fragment raised beta-3 receptor expression, but its fat-burning effect was not fully explained by that receptor.
Read the studyRat fat tissue
hGH 177-191 blocked fat synthesis as well as whole growth hormone did, but did not raise glycerol release in that model.
Read the studyThese are questions the published research has not answered.
No product containing HGH Fragment 176-191 is approved as a medicine by the FDA.
Never approved as a drug anywhere. The developer, Metabolic Pharmaceuticals, ended the obesity program on February 21, 2007, after its phase 2b trial failed. WADA's 2026 list names both AOD-9604 and hGH 176-191 as growth hormone fragments under S2.2.3, banned in and out of competition.
No human half-life has been published for HGH Fragment 176-191, so we do not draw a clearance curve. Half-lives quoted online for it are usually estimates from animal data.
This table records the doses that trials and approved labels used, with the source for each row. It is a record of research, not a recommendation, and it is open to free members.
Which symptoms are expected and which mean stop and get help: side effects and red flags.
Tap a claim to see what the studies found.
The side-effect half is supported: trials found no rise in IGF-1 and no harm to blood sugar. The fat-burning half is not: the largest human trial found no significant weight loss over 24 weeks.
That was the hypothesis from rodent fat tissue. When it was tested in obese adults, the fragment did not produce significant weight loss.
The native 176-191 sequence starts with phenylalanine, but most products sold under this name carry the tyrosine-modified AOD-9604 sequence. Unless a supplier shows otherwise, treat them as the same molecule.
No human study measured fat distribution. The claim is borrowed from growth hormone research.
One rabbit osteoarthritis study used joint injections. No human data exist.
These pairings come up often. Almost none have been tested together in a trial, and the evidence note on each says so plainly.
Marketed as pairing a fat-targeting fragment with peptides that raise the body's own growth hormone.
EvidenceNo study has tested this combination. The fragment alone failed its human weight-loss trial.
No manufacturer or published stability data for injectable forms. Freeze-dried peptides are generally kept cold, dry and out of light.
No published stability data for any reconstituted solution.
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