The key difference in one line: AOD-9604 is a stabilized, structurally modified peptide closely related to the human growth hormone C-terminal fragment 176-191 — PubChem characterizes AOD-9604 with an N-terminal tyrosine residue and a disulfide bridge, structural features used to improve metabolic stability in preclinical models. In research terms, AOD-9604 is the better-characterized of the two: it carries a documented preclinical research record and is the form most laboratory literature actually studied — many older papers labelled “HGH Fragment 176-191” used what would today be classified as AOD-9604.
For research purposes only. Not for human consumption. This article describes mechanism and characterization, not clinical or human-use outcomes.
This article gives a structured, side-by-side comparison of AOD-9604 and HGH Fragment 176-191 across structure, mechanism, stability, research context, and analytical purity. Rather than quote a fixed purity number, we point to the Certificate of Analysis (COA): we publish independent third-party Janoshik reports for tested batches, so you can check the COA / Verify badge on the product itself. All content is for educational and laboratory-research use only.
AOD-9604 vs HGH Fragment 176-191: Side-by-Side Comparison
| Attribute | AOD-9604 | HGH Fragment 176-191 |
|---|---|---|
| Sequence / structure | Closely related to the hGH 176-191 C-terminal region; PubChem (CID 71300630) lists an N-terminal tyrosine residue and a disulfide bridge | The hGH C-terminal segment, amino acids 176-191 (PubChem CID 172966176); exact sequence and any disulfide vary by preparation |
| Molecular weight (PubChem) | ~1,815 Da (C78H123N23O23S2, CID 71300630) | ~1,859 Da (C80H127N23O24S2, CID 172966176); confirm against the exact preparation in hand |
| Mechanism (as described in research) | In the cited preclinical models, lipolytic effects were attenuated in beta-3 adrenergic receptor knockout mice, indicating beta-3 dependence; did not signal through the growth hormone receptor like full-length hGH (PMID: 11673763) | Literature attributes lipolytic activity of the hGH C-terminal region to beta-adrenergic (beta-3) signaling; data for the unmodified fragment as a distinct entity are limited |
| Stability | Described as more stable in preclinical work; the structural modifications are reported to improve resistance to enzymatic degradation | Reported as less stable in the unmodified form; consult primary sources for the specific preparation |
| Research context | Developed through Metabolic Pharmaceuticals Ltd. across multiple investigational phases; preclinical lipid-metabolism studies (PMID: 11713213, 11673763), an investigational-status review (PMID: 15134286), and a later rabbit cartilage-model study (PMID: 26275694) | Thin dedicated literature as a distinct entity; many papers citing “HGH Fragment 176-191” used the AOD-9604 formulation |
| Regulatory history (neutral) | Never approved as a drug for any indication; investigated preclinically and in early-phase work | Never approved as a drug; described in the literature as a research compound |
| Purity (third-party COA) | We publish independent third-party Janoshik reports for tested batches — check the COA / Verify badge on the product. Verify a COA · how to read it | Always confirm purity and molecular weight on a per-batch COA before use — structural similarity makes HPLC and mass-spec confirmation essential to tell the two apart. Verify a COA |
| Product page | AOD-9604 (CertaPeptides) | Not stocked as a separate catalog item; discussed here as a research-literature reference entity |
Purity note: we are a reseller, not a manufacturer. We do not publish a single fixed purity number because purity is a per-batch measurement. For tested batches we publish independent third-party Janoshik reports — check the COA / Verify badge on the product, and use the verification page to view the report for the specific batch you are evaluating.
What Is AOD-9604?
AOD-9604 is a synthetic, stabilized peptide closely related to the C-terminal region (amino acids 176-191) of the human growth hormone sequence. PubChem (CID 71300630) describes its structure with an N-terminal tyrosine residue and a disulfide bridge — features reported to improve metabolic stability in preclinical models. For the exact sequence and mass, consult PubChem or the primary literature.
Research by Heffernan et al. (2001) in Endocrinology examined the metabolic activity of AOD9604 in animal models relative to full-length growth hormone, reporting differences in its influence on insulin sensitivity and glucose metabolism (PMID: 11713213). A later review by Wilding (2004) in Current Opinion in Investigational Drugs outlined the compound’s metabolic profile and investigational history (PMID: 15134286). As a point of regulatory history only, AOD-9604 was never approved as a pharmaceutical drug for any indication.
What Is HGH Fragment 176-191?
HGH Fragment 176-191 refers to the C-terminal peptide segment of human growth hormone, spanning amino acids 176 through 191 (PubChem CID 172966176). It is described as a closely related but distinct entity from AOD-9604; the exact sequence, terminal modifications, and any disulfide bridge can vary by preparation, so the molecular weight and structure on a batch COA are the reliable identifiers.
The fragment was identified early in growth hormone research as carrying much of the molecule’s lipolytic activity through the C-terminal region’s interaction with beta-adrenergic receptors — particularly the beta-3 subtype — without requiring the full receptor-binding domain responsible for hGH’s growth-promoting effects. In the scientific literature, however, the distinction between the two is often blurred: many studies discussing “HGH Fragment 176-191” effectively describe work that used the stabilized, tyrosine-modified form now classified as AOD-9604.
Mechanism of Action: How Each Compound Works
In the cited preclinical literature, the lipolytic activity of this compound class is attributed primarily to interaction with beta-3 adrenergic receptors in adipose tissue. This receptor subtype is associated with thermogenesis and lipolysis; its activation is described as triggering a cyclic AMP (cAMP) cascade that activates hormone-sensitive lipase (HSL) and releases free fatty acids from stored triglycerides.
In the Heffernan et al. (2001) study comparing full-length hGH and AOD9604 in beta-3 adrenergic receptor knockout mice, AOD9604’s lipolytic effects were significantly attenuated in knockout animals, providing evidence for beta-3 receptor dependence in that model; the same study noted AOD9604 did not produce statistically significant changes in insulin-like growth factor 1 (IGF-1) levels, unlike full-length growth hormone (PMID: 11673763). Direct head-to-head receptor-binding comparisons between AOD-9604 and the unmodified fragment in published literature are limited, so structure-activity differences should be treated as an open research question rather than a settled fact.
Research History Compared
AOD-9604 has a more developed preclinical and investigational research record than HGH Fragment 176-191 as a distinct compound. Much of this work was conducted through Metabolic Pharmaceuticals Ltd., which advanced AOD-9604 through multiple investigational phases; the Wilding (2004) review summarizes that development history (PMID: 15134286). The Heffernan et al. 2001 papers remain among the most-cited in this compound class: their Endocrinology paper compared full-length hGH, AOD9604, and saline controls in an animal model (PMID: 11713213), and a companion paper in the International Journal of Obesity examined fat oxidation in animal models (PMID: 11673763). Separately, Kwon and Park (2015) in Annals of Clinical and Laboratory Science explored AOD9604’s effects in a rabbit osteoarthritis model, examining cartilage tissue — a research area distinct from the compound’s original metabolic focus (PMID: 26275694).
HGH Fragment 176-191, as a distinct entity without the AOD-9604 modifications, has a thinner dedicated research record. Researchers sourcing or referencing this compound for in vitro or in vivo studies should verify which specific form — modified or unmodified — was used in any study they intend to replicate or build upon.
When Researchers Choose Each
When AOD-9604 is the typical reference compound
- When a study design needs to map to existing published preclinical literature — the cited body of work (PMID: 11713213, 11673763, 15134286, 26275694) used the stabilized AOD-9604 form.
- When greater stability under standard laboratory conditions is important to the assay window — the modified form is reported in preclinical work to resist enzymatic degradation better than the unmodified fragment.
- When beta-3 adrenergic receptor dependence is the variable under study, since the knockout-mouse evidence base is specific to AOD9604.
When the unmodified HGH Fragment 176-191 is the intended entity
- When the research question specifically concerns the native C-terminal sequence without the engineered modifications — for example, structure-activity comparisons against the modified analog.
- When replicating an older protocol that explicitly characterized a specific preparation in its Methods section — match the molecular weight and structure reported there against the COA in hand.
In both cases, the practical first step is the same: confirm identity and purity on a Certificate of Analysis. Because the two are closely related, HPLC purity data and mass-spectrometry molecular-weight confirmation are what actually distinguish them in hand. See the guide to reading a peptide COA for how to interpret the report.
Key Takeaways
- AOD-9604 is a stabilized peptide closely related to HGH Fragment 176-191; PubChem lists an N-terminal tyrosine and a disulfide bridge, features reported to improve metabolic stability in preclinical models.
- In the cited models, lipolytic activity is attributed to beta-3 adrenergic receptors rather than the full hGH receptor pathway that drives IGF-1 release.
- AOD-9604 has the more extensive investigational research record; the unmodified fragment has limited dedicated literature.
- Many older papers citing “HGH Fragment 176-191” used the AOD-9604 formulation — verify structural details before treating the two as equivalent.
- Identity and purity are settled by a per-batch COA (HPLC + mass spec), not by the product name — verify the COA for the exact batch.
Frequently Asked Questions
Are AOD-9604 and HGH Fragment 176-191 the same compound?
No. They are closely related but distinct entities with separate PubChem records (CID 71300630 for AOD-9604, CID 172966176 for HGH Fragment 176-191). PubChem describes AOD-9604 with an N-terminal tyrosine residue and a disulfide bridge. For the exact sequence and mass of either, consult PubChem or the primary literature.
Which compound has more published research?
AOD-9604 has significantly more published preclinical and investigational research. HGH Fragment 176-191 in its unmodified form has limited dedicated research, though some older papers use the two terms interchangeably.
Does either compound raise IGF-1 levels in research models?
Based on available preclinical data, AOD-9604 did not significantly raise IGF-1 levels in the conditions studied, in contrast to full-length growth hormone; this selectivity was noted in the Heffernan et al. (2001) studies. Data on unmodified HGH Fragment 176-191’s IGF-1 effects specifically is more limited.
What receptor do these compounds primarily act on?
Research indicates both primarily interact with beta-3 adrenergic receptors in adipose tissue. Evidence comes from studies in beta-3 receptor knockout mice, where the lipolytic effects of AOD-9604 were substantially reduced compared with wild-type animals.
How do I tell the two apart when sourcing?
By the Certificate of Analysis. Because the two are closely related, mass-spectrometry molecular weight and HPLC purity on the batch COA are what confirm which compound is in hand — match them against the PubChem record (CID 71300630 for AOD-9604, CID 172966176 for the fragment). You can verify the batch COA here.
Are these compounds approved for human use?
Neither compound is approved as a pharmaceutical drug for any indication. Both are available for in vitro and preclinical research purposes only and are not for human consumption.
References
- Heffernan M, Summers RJ, Thorburn A, et al. (2001). 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. PMID: 11713213
- Heffernan MA, Thorburn AW, Fam B, et al. (2001). 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. PMID: 11673763
- Wilding J. (2004). AOD-9604 Metabolic. Curr Opin Investig Drugs. PMID: 15134286
- Kwon DR, Park GY. (2015). Effect of Intra-articular Injection of AOD9604 with or without Hyaluronic Acid in Rabbit Osteoarthritis Model. Ann Clin Lab Sci. PMID: 26275694
Last reviewed: June 2026. Disclaimer: This article is for educational and research purposes only. The information provided does not constitute medical advice, and no claims are made regarding the therapeutic efficacy of any compound discussed. CertaPeptides is a reseller of research compounds, not a manufacturer; products are sold for laboratory research use only and are not intended for human consumption. Certificate of Analysis available for verification. Consult applicable regulations in your jurisdiction.
Overte pred výskumom
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