What is HGH fragment 176-191, and what is AOD-9604
HGH fragment 176-191 and AOD-9604 both refer to the same 16-residue stretch at the tail end of human growth hormone, the part responsible for the hormone's effect on fat metabolism. On its own, this domain drives lipolysis in fat tissue without triggering the growth-promoting or blood-sugar effects that come from the rest of the 191-residue hormone.
The two names are not fully interchangeable. Fragment 176-191, sometimes written hGH 177-191 depending on the numbering convention used, typically means the native, unmodified sequence isolated from human growth hormone. AOD-9604 is a specific, chemically modified version of that same domain, developed by Professor Frank Ng's group at Monash University and later taken into human trials by Metabolic Pharmaceuticals. For each compound's own history in detail, see our fragment 176-191 overview and AOD-9604 research overview.
The one-residue difference and why it exists
The distinction comes down to a single substitution. The native fragment retains phenylalanine at the first position of the domain. AOD-9604 replaces that residue with tyrosine, a change made originally to allow the peptide to be radiolabeled for tracking studies in animals, not to improve its biological activity.
That one substitution also shifts the numbering some papers use. Because the added tyrosine sits ahead of the original sequence, AOD-9604 is occasionally labeled Tyr-hGH 177-191 rather than 176-191. Researchers cross-referencing older and newer papers need to check which numbering convention, and which residue at position one, a given source is actually using.
Research evidence: the trial record belongs to AOD-9604
The earliest published work on this domain used the unmodified sequence. A 1994 study by Natera, Jiang, and Ng in Biochemistry and Molecular Biology International treated obese (ob/ob) mice with synthetic hGH 177-191 and found reduced cumulative body weight gain, decreased adipose tissue mass, and significantly inhibited lipogenesis in fat tissue.
Nearly every quantitative result published after that point used AOD-9604 specifically, not the native fragment. A 2000 study by Ng et al. in Hormone Research gave obese Zucker rats an oral dose of 500 mcg/kg AOD-9604 daily for 19 days and recorded body weight gain of 15.8 plus or minus 0.6 grams, versus 35.6 plus or minus 0.8 grams in untreated controls, with no adverse change in insulin sensitivity on euglycemic clamp testing. A related 2000 paper in the Journal of Molecular Endocrinology (Ng et al.) reported that 20 days of treatment with the closely related AOD9401 construct shrank average adipocyte diameter in Zucker rats from 110 to 80 micrometers.
A direct head-to-head test appears in a 2001 paper in the International Journal of Obesity (Heffernan et al.). Obese mice given either intact hGH or AOD9604 for 14 days both lost weight and showed increased fat oxidation and plasma glycerol, a lipolysis marker. Unlike hGH, AOD9604 did not raise blood glucose or reduce insulin secretion, and receptor-binding assays confirmed it does not compete for the hGH receptor or trigger the cell proliferation that intact hGH does.
All six human clinical trials on this compound, including the 502-subject Phase 2b obesity study that ended the original development program in 2007, were run on AOD-9604. The native fragment has never been tested in a registered human trial under its own name.
Same lipolytic pathway, an incompletely mapped mechanism
Both hGH and AOD9604 raise expression of the beta-3-adrenergic receptor (beta3-AR), the main lipolytic receptor in rodent fat tissue, back toward normal levels in obese mice. A 2001 study in Endocrinology (Heffernan et al.) found that chronic treatment with either compound in beta3-AR knockout mice failed to reduce body weight or increase lipolysis, unlike the response seen in normal mice.
The same study complicates a simple beta3-AR explanation. In a shorter acute test, AOD9604 still raised energy expenditure and fat oxidation in the same knockout mice. The authors concluded that the lipolytic action is not directly mediated through beta3-AR alone, even though the peptide raises the receptor's expression. The full signaling chain between peptide binding and fat breakdown has not been worked out for either sequence.
Where the two names diverge in current research
Since the obesity program closed, new research tied to this compound's history has used the AOD-9604 name, not the native fragment's. A 2013 study in Drug Testing and Analysis (Orlovius et al.) tested whether AOD-9604 interferes with the World Anti-Doping Agency's hGH isoform immunoassay, the test used to detect banned growth hormone doping in athletes, and found no interference.
A 2015 study in Annals of Clinical and Laboratory Science (Kwon and Park) injected AOD9604 directly into the knee joints of 32 rabbits with collagenase-induced osteoarthritis, split across four groups: saline, hyaluronic acid, AOD9604 alone, and AOD9604 combined with hyaluronic acid. Cartilage degeneration scores were lowest and lameness resolved fastest in the combined group. This is joint-injection data in an animal model, unrelated to the compound's original metabolic research, and no published human trial has followed it.
Most recently, AOD-9604 was relicensed under the name LAT8881 for a completed Lateral Pharma trial registered as NCT05298306, with results posted in November 2024. Part A gave ascending intravenous doses, 0.8 to 1.8 mg/kg, to 8 healthy volunteers to assess safety. Part B tested a single intravenous dose against placebo in up to 20 patients with lumbar radicular pain, a sciatica-type nerve pain condition unrelated to fat metabolism. None of this newer work has been conducted under the fragment 176-191 name.
Regulatory status and practical handling for research use
Neither compound has FDA approval for any indication. AOD-9604 holds self-affirmed GRAS (Generally Recognized as Safe) status for use in foods and dietary supplements, based on a safety database covering more than 800 subjects across its oral trials, and as of mid-2026 sits under FDA Pharmacy Compounding Advisory Committee Category 2 review for compounding use. No comparable regulatory filing exists for the native, unmodified fragment.
In practice, most vials sold as fragment 176-191 and most sold as AOD-9604 are handled the same way: lyophilized powder, cold-chain sensitive, reconstituted with bacteriostatic water before use. Because the name on a label does not guarantee which residue sits at position one of the sequence, researchers who need to confirm which variant they have should check the certificate of analysis rather than relying on the name alone; see our guide to reading a peptide COA if one is unclear.
Storage and shipping considerations are otherwise identical for both. Researchers receiving shipments in Indonesia, particularly outside Jakarta and Bali where cold-chain logistics are less consistent, should keep vials lyophilized until use and aliquot before freezing to limit freeze-thaw exposure; the lyophilized peptide storage guide covers the relevant temperature and shelf-life data. For reconstitution volumes and concentration math once a protocol specifies a dose, the dosing calculator handles the standard conversions.