▶ FRAG 176-191 · SUBTOPIC · MECHANISM

FRAG 176-191 Mechanism

For Laboratory Research Use Only. The mechanistic information below is descriptive of published research. No human dose is recommended. No clinical claim is made.

MECHANISM OF ACTION

16-amino-acid C-terminal fragment of human growth hormone (residues 176-191), also known as AOD-9604 in its modified form. Retains the lipolytic activity of the parent HGH without IGF-1 elevation or anabolic effects. Drives beta-3-adrenergic fat oxidation in adipose tissue.

PHARMACOKINETIC HALF-LIFE

Reported half-life for FRAG 176-191: ~30 minutes (rapid plasma clearance). Half-life determines the kinetic window across which receptor occupancy is maintained and frames the dosing rhythm used in published literature.

PRIMARY SEQUENCE

FRAG 176-191 is a defined sequence: Tyr-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe (residues 176-191 of human GH). Synthesis proceeds via solid-phase peptide synthesis with HPLC-verified identity confirmation.

MECHANISM CATEGORIES

FRAG 176-191 is tagged in 2 mechanism categories on PEPPUDEX. Each category aggregates the broader pharmacology of related compounds.

▶ LIPOLYSIS

Lipolysis is the breakdown of triglycerides in adipose tissue, driven by hormone-sensitive lipase activation downstream of cAMP elevation. GH-axis peptides (GH-axis reference) preferentially target visceral adipose. Glucagon-receptor agonism (the third arm of GLP-1) also drives hepatic lipid mobilization.

▶ METABOLIC REGULATION

Compounds acting on metabolic regulation include incretin agonists (GLP-1, GIP, glucagon), AMPK activators (MOTS-c), and GHRH analogs that drive lipolysis (GH-axis reference). The shared therapeutic target is metabolic dysfunction underlying obesity, type 2 diabetes, NAFLD, and the broader cardiometabolic syndrome.

MECHANISTIC OUTCOMES IN LITERATURE

The following outcomes are the mechanistic endpoints reported in the peer-reviewed literature, with PEPPUDEX evidence grades. Grades reflect study quality and replication, not clinical recommendation.

▶ Lipolytic activity (in vitro / animal)GRADE B

Ng et al. 2000 (PMID 10681682) demonstrated retention of HGH lipolytic activity in the 176-191 fragment without IGF-1 elevation.

▶ Safety profile (human Phase 2 of AOD9604 modified form)GRADE B

Stier et al. 2013 reported Phase 2 safety/tolerability of the AOD9604 modified form in obesity.

▶ Body composition (long-term human)GRADE D

No completed long-term Phase 3 trials for either the raw fragment or the AOD9604 modified form.

MECHANISM Q+A

▶ Frag 176-191 vs AOD-9604 · what's the difference?

Frag 176-191 is the raw native sequence of HGH residues 176-191. AOD-9604 is the same fragment with an N-terminal tyrosine modification developed by Metabolic Pharmaceuticals to stabilize the molecule for clinical development. Same lipolytic core mechanism; AOD9604 is the formulation that entered Phase 2 obesity trials.

▶ Frag 176-191 vs HGH · which is safer?

Different molecules with different outcomes. HGH (full sequence) elevates IGF-1 and produces both lipolysis and systemic anabolism. Frag 176-191 retains only the lipolytic arm with no IGF-1 elevation, eliminating the major class-level side-effect concerns (gigantism, insulin resistance, certain tumor risk signals). Frag 176-191 has a much narrower mechanism but a safer profile in published data.

▶ How does Frag 176-191 work?

The C-terminal fragment retains the beta-3-adrenergic-receptor-mediated lipolytic signaling of the parent HGH while losing the IGF-1-axis activation (which requires the N-terminal portion of HGH for receptor binding). The result is fat oxidation without anabolic effects.

▶ What is the half-life of Frag 176-191?

Approximately 30 minutes plasma half-life. Daily subcutaneous administration is the standard research protocol.

▶ Can Frag 176-191 be stacked with GLP-3?

Different mechanisms. GLP-3 drives central appetite suppression via GLP-1R; Frag 176-191 drives peripheral lipolysis via beta-3-adrenergic signaling. The pathways are non-overlapping and theoretically complementary. No published combination data exists in human research.

CITED LITERATURE

Ng FM, Sun J, Sharma L, et al.. Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Horm Res 2000. PMID 10681682. link
Stier H, Vos E, Kenley D. Safety and tolerability of the hexadecapeptide AOD9604 in humans. J Endocrinol Invest 2013. link

◀ FRAG 176-191 OVERVIEW DOSING LITERATURE ▶SAFETY PROFILE ▶

▶ LAST UPDATED · 2026-05-25