Quick Comparison
| HGH Fragment 176-191 | VK2735 | |
|---|---|---|
| Half-Life | 0.5-1 hours | Approximately 144-168 hours (6-7 days), supporting once-weekly dosing |
| Typical Dosage | Research: 250-500 mcg subcutaneous once or twice daily, on an empty stomach. Often cycled 8-12 weeks on, 4 weeks off. The short half-life typically requires twice-daily dosing for sustained effect. | Phase 2 (subcutaneous): doses of 2.5, 5, 10, and 15 mg once weekly with stepwise escalation. The 15 mg arm produced the maximum weight loss of 14.7% at 13 weeks. Oral formulation in Phase 1: 30-100 mg daily, dose escalation ongoing. |
| Administration | Subcutaneous injection | Subcutaneous injection (once weekly); oral tablet formulation in earlier development |
| Research Papers | 1 papers | 1 papers |
| Categories |
Mechanism of Action
HGH Fragment 176-191
HGH Fragment 176-191 is the unmodified C-terminal segment of human growth hormone, representing exactly the last 16 amino acids of the 191-amino-acid GH molecule. Research identified this region as containing the molecular determinants responsible for GH's lipolytic activity, independent of the N-terminal domain that binds the growth hormone receptor and drives IGF-1 production and tissue growth.
The fragment activates lipolysis in white adipose tissue through interaction with beta-adrenergic signaling pathways. This triggers the cAMP/protein kinase A cascade that phosphorylates and activates hormone-sensitive lipase and perilipin proteins on the surface of lipid droplets within fat cells. The result is the breakdown of stored triglycerides into free fatty acids and glycerol, which are released into circulation for oxidation by energy-demanding tissues such as skeletal muscle and the liver.
Because the fragment lacks the binding regions for the GH receptor (located in amino acids 1-175), it does not activate the JAK2-STAT5 signaling pathway responsible for hepatic IGF-1 synthesis, somatic growth, or the insulin-antagonistic effects of full-length growth hormone. However, the shorter half-life compared to AOD-9604 (which has an additional stabilizing tyrosine residue) means more frequent dosing is required, and clinical evidence supporting its efficacy in humans remains very limited.
VK2735
VK2735 is a once-weekly subcutaneous dual GLP-1/GIP receptor agonist with a structure optimised for high potency and a clean tolerability profile. Dual incretin receptor activation produces complementary effects on appetite, glucose handling, and energy expenditure: GLP-1 receptor agonism delivers central appetite suppression through hypothalamic arcuate-nucleus signalling, slows gastric emptying, and triggers glucose-dependent insulin secretion, while GIP receptor activation amplifies the insulin response, supports beta-cell function, and modulates adipose tissue lipid handling.
The molecule's pharmacokinetic profile delivers sustained receptor exposure across a one-week dosing interval, achieved through structural modifications that enable albumin binding and resistance to proteolytic degradation. In the Phase 2 VENTURE trial, the 15 mg dose produced 14.7% mean body weight loss at 13 weeks — the fastest early weight loss observed for any obesity drug, with the loss curve still descending steeply at trial end. This rapid trajectory suggests substantially greater total weight loss would be achievable with longer dosing, and Phase 3 VANQUISH trials launched in 2026 are testing 68-week treatment durations to characterise the full magnitude of effect.
Viking is also developing an oral tablet formulation of VK2735 in parallel, which entered Phase 1 in 2024-2025. If both formulations succeed, Viking would have one of the most flexible GLP-1/GIP product profiles on the market — though as a small biotech company it faces significant manufacturing and commercial scaling challenges relative to Lilly and Novo Nordisk.
Risks & Safety
HGH Fragment 176-191
Common
injection site irritation, headache, brief dizziness.
Serious
extremely limited clinical data, no long-term safety information.
Rare
allergic reactions.
VK2735
Common
nausea, vomiting, diarrhea, constipation, decreased appetite, injection site reactions. Discontinuation rates in Phase 2 were broadly similar to other GLP-1/GIP dual agonists.
Serious
pancreatitis, gallstones, possible muscle mass loss.
Rare
thyroid C-cell tumour class warning, severe allergic reactions. Long-term safety being established in Phase 3.
Full Profiles
HGH Fragment 176-191 →
The original, unmodified version of the growth hormone fat-burning fragment — essentially the same concept as AOD-9604 but less stable and shorter-lasting. Contains the part of growth hormone responsible for fat metabolism without the parts that cause growth or blood sugar issues. Requires more frequent dosing than AOD-9604, and has even less clinical evidence supporting its effectiveness.
VK2735 →
Viking Therapeutics' once-weekly weight loss injection that, like tirzepatide, hits both the GLP-1 and GIP receptors. In a 13-week Phase 2 trial it produced 14.7% mean body weight loss — the steepest early loss curve recorded for any obesity drug — and Phase 3 VANQUISH trials began in 2026. An oral tablet version is also in earlier development. Viking is one of the only small biotech companies competing directly with Lilly and Novo Nordisk in the GLP-1 space.