HGH Fragment 176-191: Research, Results & Side Effects (2026)

HGH Fragment 176-191 is a short synthetic peptide copied from the C-terminal end of human growth hormone (hGH), the region researchers linked to growth hormone's effects on fat metabolism. In animal studies, this region and its tyrosine-modified analog AOD-9604 reduced weight gain and increased fat breakdown in obese rodents without raising blood glucose or binding the growth hormone receptor. Human evidence is thin: the analog reached early obesity trials in the 2000s but was never approved, and HGH Fragment 176-191 is not an FDA-approved drug.

This guide covers what the fragment is, the proposed mechanism, what the studies actually measured, what is known about side effects, and where it stands with the FDA in October 2026.

Educational content for licensed healthcare professionals. Not medical advice; dosing and treatment decisions belong to the prescribing clinician.

HGH Fragment 176-191 at a Glance

What Is HGH Fragment 176-191?

Human growth hormone is a 191-amino-acid protein. In the 1990s, a group at Monash University in Australia studied whether its metabolic effects on fat could be separated from its growth-promoting effects. They synthesized short peptides from the hormone's C-terminal end and tested them in fat tissue and obese rodents.

The first work used the 177-191 sequence. Wu and Ng reported in 1993 that synthetic hGH 177-191 reproduced the antilipogenic (fat-storage-blocking) activity of the intact hormone in rat fat tissue [1]. A 1994 follow-up found that chronic treatment of obese (ob/ob) mice with hGH 177-191 reduced cumulative weight gain and adipose tissue mass [2].

The group then developed a modified version with an added N-terminal tyrosine, named AOD-9604 (sometimes AOD9604). Because that tyrosine extends the 177-191 sequence by one residue, the analog is frequently labeled "176-191," and the research market's "HGH Fragment 176-191" and AOD-9604 are often the same or near-identical molecule. The AOD-9604 library page covers that analog in detail. Practically, most of the published literature on "the fragment" is literature on AOD-9604.

For the library overview of the compound, see our HGH Fragment 176-191 page.

How It Is Thought to Work

Growth hormone does several things at once: it promotes growth through IGF-1, it raises blood glucose and reduces insulin sensitivity, and it mobilizes fat. The fragment hypothesis is that the fat-mobilizing action lives in the C-terminal region and can be isolated.

What the Monash studies observed:

• Lipolysis and fat oxidation. In obese mice treated for 14 days, both intact hGH and AOD-9604 reduced body-weight gain, increased fat oxidation, and raised plasma glycerol, a marker of lipolysis [3].
• No growth hormone receptor binding. In cells engineered to express the hGH receptor, AOD-9604 did not compete for receptor binding and did not drive cell proliferation, unlike hGH [3].
• No hyperglycemia. Unlike intact hGH, AOD-9604 did not induce hyperglycemia or reduce insulin secretion in those mice [3]. In obese Zucker rats, chronic treatment did not impair insulin sensitivity on euglycemic clamp testing [4].
• Beta-3 adrenergic involvement. Both hGH and AOD-9604 increased beta-3 adrenergic receptor expression in fat of obese mice, and long-term effects were lost in beta-3 receptor knockout mice, although an acute increase in fat oxidation persisted [5].

These findings are the basis for the common description "lipolysis without the anabolic or diabetogenic effects of growth hormone." That description is accurate for what was measured in rodents. It has not been demonstrated in controlled human studies of the 176-191 fragment.

What the Research Actually Shows

It helps to sort the evidence by type:

In vitro and animal studies (most of the evidence). The papers above, all from one research lineage, consistently show reduced weight gain and increased lipolysis in obese rodent models. They are small, short, and largely from the developer's group. Independent replication is limited.

Human development (AOD-9604). AOD-9604 was taken into clinical development for obesity by the Australian company Metabolic Pharmaceuticals; a 2004 drug profile reported that phase IIa trials were under way by early 2002 [6]. It did not become an approved obesity drug, and full efficacy results from that program are not available in peer-reviewed journals indexed in PubMed. Claims online about specific human weight-loss percentages should be treated with caution unless a published source is provided.

Musculoskeletal research. AOD-9604 has also been studied in a rabbit osteoarthritis model, where it was given intra-articularly with or without hyaluronic acid and was associated with better cartilage scores [7]. That is an animal study of a different application, and it should not be read as evidence for fat loss.

Recent reviews. A 2026 narrative review of GH-axis peptides used outside regulatory oversight places AOD9604 (labeled hGH 176-191) among compounds where clinicians face real uncertainty about product composition and effect, and stratifies these agents by evidence tier, from regulatory-grade trials down to no human studies [8]. A 2026 sports-medicine review similarly concluded that many unapproved peptides, AOD-9604 included, look favorable in animal models while rigorous human safety data are scarce [9].

The honest summary: the mechanism is plausible and the animal data are consistent, but there is no published randomized human efficacy trial of HGH Fragment 176-191 itself.

Side Effects and Safety

Because there are no published, adequately sized human trials of the fragment, its side-effect profile in people is not well characterized. What can be said:

• Theoretical advantage over hGH. In rodents it did not cause hyperglycemia or cell proliferation through the GH receptor [3, 4]. That is a mechanistic point in animals, not a demonstrated human safety profile.
• Reported effects in clinical practice and reviews. Reviews of unregulated GH-axis peptides describe injection-site reactions, appetite changes, and other nonspecific effects across the class [8]; these are not attributed specifically to the fragment in controlled studies.
• Product quality is a real risk. Regulators have seized unlabeled preparations later identified as AOD-9604 [10]. When a compound is sold outside the drug-approval system, identity, purity, sterility, and potency are uncertain. Sourcing through a state-licensed 503A pharmacy with a valid prescription, where the substance is eligible for compounding, addresses part of that risk.
• Anti-doping. Anti-doping laboratories have developed detection methods for AOD-9604 [11]. Competitive athletes should check current anti-doping rules before any use.

Patients with active malignancy, pregnancy, uncontrolled metabolic disease, or other complex conditions were not studied, and the absence of data is itself a reason for caution.

Regulatory Status in 2026

HGH Fragment 176-191 is not FDA-approved for any indication. It does not appear as its own row on our FDA peptide status tracker, and we have not confirmed a current 503A interim category for it, so prescribers should check the tracker and their partner pharmacy before assuming it can be compounded. The July 2026 PCAC meeting did not consider it, and it is not on the agenda for the second PCAC meeting expected before the end of February 2027.

For background on how 503A eligibility works, see Which Peptides Are Legal to Compound in 2026?.

How It Fits With Other Fat-Loss Options

Clinicians weighing the fragment usually compare it against agents with stronger evidence. Growth hormone-releasing approaches such as tesamorelin (FDA-approved as Egrifta for HIV-associated abdominal fat) and the GLP-1 class have randomized human data that the fragment lacks. Our overview of growth hormone peptides for fat loss sets the options side by side.

Frequently Asked Questions

What is HGH Fragment 176-191 used for?

It is marketed for fat loss because animal studies of the growth hormone C-terminal fragment and its analog AOD-9604 showed increased lipolysis and reduced weight gain in obese rodents. It is not FDA-approved for any use, and there is no published randomized human efficacy trial of the 176-191 fragment itself.

Does HGH Fragment 176-191 raise IGF-1?

In the published animal and cell work, the related analog AOD-9604 did not bind the growth hormone receptor and did not cause hyperglycemia, which is why it is described as lacking growth hormone's anabolic effects. That has not been confirmed in controlled human studies.

Is HGH Fragment 176-191 the same as AOD-9604?

Often, in practice. AOD-9604 is the hGH 177-191 sequence with an added tyrosine, which is why it is frequently labeled 176-191. Confirm the stated sequence on the pharmacy's certificate of analysis.

What are the side effects of HGH Fragment 176-191?

Human side effects are not well characterized because adequate trials have not been published. Reviews of unregulated GH-axis peptides describe injection-site reactions and nonspecific effects, and product purity is a major concern outside licensed pharmacies.

What dose of HGH Fragment 176-191 is used?

This guide does not give one. No human dose has been established through published trials, and dosing is a decision for the prescribing clinician.

Is HGH Fragment 176-191 legal to compound?

It is not FDA-approved, and its 503A status should be checked on our FDA peptide status tracker and with the compounding pharmacy before prescribing.

References

1. Wu Z, Ng FM. Antilipogenic action of synthetic C-terminal sequence 177-191 of human growth hormone. Biochem Mol Biol Int. 1993;30(1):187-96. PubMed
2. Natera SH, et al. Reduction of cumulative body weight gain and adipose tissue mass in obese mice: response to chronic treatment with synthetic hGH 177-191 peptide. Biochem Mol Biol Int. 1994;33(5):1011-21. PubMed
3. Heffernan MA, et al. Increase of fat oxidation and weight loss in obese mice caused by chronic treatment with human growth hormone or a modified C-terminal fragment. Int J Obes Relat Metab Disord. 2001;25(10):1442-9. PubMed
4. Ng FM, et al. Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Horm Res. 2000;53(6):274-8. PubMed
5. Heffernan M, et al. The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and beta(3)-AR knock-out mice. Endocrinology. 2001;142(12):5182-9. PubMed
6. Wilding J. AOD-9604 Metabolic. Curr Opin Investig Drugs. 2004;5(4):436-40. PubMed
7. Kwon DR, Park GY. Effect of intra-articular injection of AOD9604 with or without hyaluronic acid in rabbit osteoarthritis model. Ann Clin Lab Sci. 2015;45(4):426-32. PubMed
8. Dominikowski A, et al. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Front Endocrinol (Lausanne). 2026;17:1822475. PubMed
9. Mendias CL, Awan TM. Safety and efficacy of approved and unapproved peptide therapies for musculoskeletal injuries and athletic performance. Sports Med. 2026;56(8):1921-1935. PubMed
10. Vanhee C, et al. Identification and characterization of peptide drugs in unknown pharmaceutical preparations seized by the Belgian authorities: case report on AOD9604. Drug Test Anal. 2014;6(9):964-8. PubMed
11. Cox HD, et al. Detection and in vitro metabolism of AOD9604. Drug Test Anal. 2015;7(1):31-8. PubMed

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