What is HGH fragment 176-191
HGH fragment 176-191 is the last 16 amino acids of human growth hormone, the stretch that carries the hormone's fat-burning activity on its own. Cut away from the rest of the 191-residue protein, it still drives lipolysis in adipose tissue but does not raise IGF-1 or trigger the insulin resistance associated with full-length growth hormone. It sits alongside other growth-hormone-pathway compounds in our research peptide catalog.
The same molecule has carried several names as it moved through three decades of research: hGH 177-191 in the earliest papers, then AOD9401, then AOD9604, and most recently LAT8881 after a 2021 licensing deal. The numbering shifts (177-191 versus 176-191) and the small chemical modifications between versions reflect different rounds of optimizing the peptide for oral dosing and stability, not different biology. For the compound's branded clinical trial history and current regulatory status, see our AOD-9604 research overview. This article covers the fragment itself: how researchers found it, what it does in tissue, and where the research has gone since.
How researchers mapped the fragment
Growth hormone's activities do not sit in one place on the molecule. Its growth-promoting and IGF-1-raising effects come mostly from the N-terminal region, where the protein binds the GH receptor and drives cell proliferation. Its lipolytic activity turned out to be separable, sitting in the C-terminal tail.
Frank Ng's group at Monash University's Department of Biochemistry and Molecular Biology described the first version of the isolated tail in 1994: a synthetic peptide spanning residues 177-191, tested in obese (ob/ob) mice (Natera et al., Biochem Mol Biol Int, 1994). Treated mice gained less cumulative body weight and carried less adipose tissue mass than controls, and lipogenesis in their fat tissue was suppressed. The paper's conclusion was blunt: this 15-residue piece looked like the antilipogenic domain of the intact hormone.
The same lab refined the construct over the following years. A 2000 paper on AOD9401 (residues 177-191) in obese Zucker rats reported that 20 days of treatment shrank average adipocyte diameter from 110 to 80 micrometers and stimulated hormone-sensitive lipase while inhibiting acetyl-CoA carboxylase, the enzyme that drives fat storage (Ng et al., J Mol Endocrinol, 2000). A companion study that same year moved to oral dosing: AOD9401 given by mouth to ob/ob mice for 30 days (n=8 saline, n=10 treated) produced significantly lower weight gain from day 16 onward, with no difference in food intake between groups, which pointed to a metabolic rather than an appetite effect (Heffernan et al., Am J Physiol Endocrinol Metab, 2000).
AOD9604, the version that carried into human trials, differs slightly in its terminal residues and was designed for better oral stability. In obese Zucker rats given 500 mcg/kg per day orally for 19 days, AOD9604 cut body weight gain by more than half compared with controls (15.8 plus or minus 0.6 grams versus 35.6 plus or minus 0.8 grams), and euglycemic clamp testing found no adverse change in insulin sensitivity, unlike chronic dosing with intact growth hormone (Ng et al., Horm Res, 2000).
Mechanism: lipolysis without the growth hormone receptor
The core finding across this body of work is that the fragment does not act like a small piece of growth hormone signaling through the same channel. Receptor-binding assays using BaF-B03 cells transfected with the hGH receptor found that AOD9604 does not compete for that receptor and does not trigger the cell proliferation that full-length hGH does, even though both molecules reduce body weight gain and raise plasma glycerol, a lipolysis marker, in obese mice (Heffernan et al., Int J Obes Relat Metab Disord, 2001).
A follow-up study looked at the beta-3-adrenergic receptor (beta3-AR) pathway, the main lipolytic receptor on fat cells, using beta3-AR knockout mice. Both hGH and AOD9604 raised beta3-AR expression back toward normal levels in obese mice after 14 days of treatment, and the weight-loss and lipolysis effects disappeared in knockout animals given long-term treatment. But in a shorter acute test, AOD9604 still increased energy expenditure and fat oxidation in the same knockout mice, so the authors concluded the lipolytic action is not directly mediated by beta3-AR itself, even though the peptide raises its expression (Heffernan et al., Endocrinology, 2001). In plain terms: the receptor is involved in the broader metabolic adaptation, but it is not the whole story, and the exact signaling path from fragment binding to fat breakdown is still not fully mapped.
What the human trial record shows
By February 2002, AOD9604 had reached Phase IIa testing under its original developer, Metabolic Pharmaceuticals (Wilding, Curr Opin Investig Drugs, 2004). The program continued into a larger Phase IIb obesity trial before development for that indication was eventually discontinued; our AOD-9604 overview covers that trial and its outcome in detail.
What is worth noting here is where the compound went next. Rebranded as LAT8881, it entered a completed Phase 1 study on lumbar radicular pain (sciatica-type nerve pain), sponsored by Lateral Pharma and registered as NCT05298306 on ClinicalTrials.gov, with 26 participants enrolled. That is a different indication entirely from the original fat-loss framing, and it reflects a broader pattern in this compound's history: research keeps circling back to it for reasons unrelated to the metabolic story that first put it on the map.
Newer research directions
Two more recent lines of research are worth flagging separately, since neither shows up in most summaries of this compound.
A 2015 study injected AOD9604 directly into the knee joints of rabbits with collagenase-induced osteoarthritis. Thirty-two rabbits were split into four groups (saline, hyaluronic acid, AOD9604 alone, and AOD9604 combined with hyaluronic acid), given weekly injections for four to seven weeks and evaluated at eight weeks. Cartilage degeneration scores were lowest, and lameness resolved fastest, in the combined AOD9604-plus-hyaluronic-acid group compared with any single treatment (Kwon and Park, Ann Clin Lab Sci, 2015). This is animal data in a joint-injection model, not evidence for the metabolic uses the compound is usually discussed for, and it has not been followed by a published human trial.
Separately, an anti-doping laboratory tested whether AOD-9604 interferes with the World Anti-Doping Agency's hGH isoform immunoassay, the test used to detect banned growth hormone doping, and found no interference (Orlovius et al., Drug Test Anal, 2013). The question mattered because the fragment shares sequence with hGH, and regulators wanted to know whether it could mask or mimic a positive result.
Practical considerations for research handling
hGH fragment 176-191 ships and stores as a lyophilized powder, the same practical category as most other research peptides sold here. The reconstitution, cold-chain, and freeze-thaw considerations that apply to any lyophilized peptide apply here too. Our lyophilized peptide storage guide covers temperature and shelf-life data relevant to Indonesia's climate, and the dosing calculator handles the concentration math once a study protocol specifies a dose in mcg/kg.
One handling mistake specific to this compound is confusing the numbering conventions. Older literature refers to hGH 177-191 or AOD9401; newer material refers to AOD9604 or LAT8881 using the 176-191 numbering. These are related but not identical constructs, and a research protocol written against one should not be assumed to transfer exactly to another without checking which sequence and modification the source paper actually used.