HGH Fragment 176-191

HGH Fragment 176-191 is a synthetic 16-amino-acid peptide copied from the tail end of human growth hormone: residues 177-191 plus an added tyrosine at the front ¹. It is the same molecule developed under the name AOD9604 ¹.

It was engineered to capture growth hormone's fat-mobilizing (lipolytic) activity while leaving behind intact hormone's effects on blood sugar ¹. In rodents it cut weight gain, raised fat oxidation, and increased lipolysis markers, without the insulin-sensitivity problems intact growth hormone causes ².

A phase IIa obesity trial program was underway by February 2002 ¹², and the compound stayed catalogued in clinical-development reviews through 2012 ¹³. No human efficacy results were ever published. Today the peptide is not approved in any jurisdiction, is sold as an unregulated research compound ¹⁷, and is prohibited in sport by WADA ¹.

Evidence at a glance

• Human trials: initiated only; no published outcomes ¹²
• Animal metabolic data: strong and consistent ²
• Cartilage: one rabbit osteoarthritis study ¹⁰
• Cancer: in-vitro work only ¹¹

AOD9604 does not act through the growth hormone receptor. In cells engineered to carry the hGH receptor, it failed to compete for growth hormone binding and did not trigger receptor-driven cell growth ³. Its fat effects run through other pathways.

Blocking new fat (antilipogenesis). The 177-191 sequence carries growth hormone's fat-synthesis-inhibiting domain. Chronic treatment reduced weight gain, fat-tissue mass, and fat synthesis in ob/ob mice ⁵. A key contributor is glucose: the fragment lowers both basal and insulin-stimulated glucose uptake in isolated fat cells, more potently than intact growth hormone at equal concentration ⁶. Less glucose entering fat cells means less raw material for triglycerides.

Priming fat release (lipolytic sensitization). Chronic AOD9604 treatment restores beta3-adrenergic receptor RNA in obese mice toward lean-animal levels, which increases sensitivity to fat-mobilizing signals ⁴. The effect is not purely beta3-dependent: acute increases in energy expenditure and fat oxidation persisted in mice lacking beta3 receptors entirely ⁴. The emerging model is dual action: block new fat formation, and make stored fat more responsive to release signals.

Insulin and muscle effects. In isolated rat islets, the fragment potentiates glucose-stimulated insulin release only at high glucose concentrations, without changing cAMP ⁹. In muscle it shifts glycogen synthase toward its inactive form, reducing glycogen synthesis capacity ⁸. Unlike intact growth hormone, chronic treatment in rats preserved insulin sensitivity on euglycemic clamp ².

No published human pharmacokinetics exist. Oral activity is documented in rodents at 500 mcg/kg/day ². In-vitro work shows the parent peptide degrades quickly in serum, while one metabolite, CRSVEGSCG, is substantially more stable ¹.

Every efficacy claim below is preclinical. Human trial entry is documented, but no human outcomes were published ¹².

Body weight and fat

• Zucker rats, oral 500 mcg/kg/day for 19 days: body-weight gain cut by more than half, lipolytic activity raised, and insulin sensitivity preserved on euglycemic clamp ²
• ob/ob mice, 14-day chronic infusion: reduced weight gain, increased fat oxidation, raised plasma glycerol (a lipolysis marker), with no hyperglycemia and no insulin-secretion suppression ³
• Beta3-adrenergic receptor knockout mice: chronic weight effects disappeared without the receptor, while acute energy-expenditure and fat-oxidation increases persisted ⁴
• Early fragment work: hGH 177-191 reduced cumulative weight gain and fat-tissue mass ⁵, inhibited fat synthesis in fat pads ⁷, and reduced glucose uptake in isolated fat cells ⁶

Cartilage

One rabbit osteoarthritis study found that weekly ultrasound-guided intra-articular 0.25 mg AOD9604 for 4-7 weeks improved cartilage degeneration and lameness scores versus saline. The combination of 0.25 mg AOD9604 plus 6 mg hyaluronic acid beat either treatment alone ¹⁰.

Cancer cells (in-vitro)

Nanoparticles loaded with both doxorubicin and the fragment curbed MCF-7 breast cancer cell growth more than doxorubicin-loaded nanoparticles alone ¹¹.

Human evidence

Detection methods are validated in human matrices: urine limits of detection around 50 pg/mL with solid-phase extraction ¹ and 50-500 pg/mL with direct-injection screening ²⁰. Efficacy in humans remains unproven ¹².

Community fat-loss protocols most commonly use 250-500 mcg per day total, injected subcutaneously in one or two injections, for 8-12 weeks, often in the fasted state or before cardio. A split-dosing variant uses 150-250 mcg two to three times daily for 4-8 weeks. An oral variant circulates at 300-500 mcg per day for 8-12 weeks, justified by rat oral data ². A 5-days-on, 2-days-off pattern is also reported. None of these schedules is validated in humans.

The only published weight-adjusted dose is preclinical: 500 mcg/kg/day orally for 19 days in obese Zucker rats ², alongside 14-day continuous delivery in ob/ob mice ³.

Timing logic

The mechanism is peripheral rather than appetite-driven: the fragment raises beta3-adrenergic receptor expression in fat tissue and increases fat oxidation without changing caloric intake in the model where this was measured ³. Community practice times doses in the fasted morning, 30-60 minutes before fasted cardio, or before the day's largest meal to blunt post-meal fat synthesis.

Duration

Animal effects appeared within 14-19 days ². Community consensus places the peak fat-loss rate at weeks 4-8, with cycles capped at 8-12 weeks. No human dose-finding data exist, so no schedule above derives from human trials ¹².

HGH Fragment 176-191 is supplied as a lyophilized (freeze-dried) powder, commonly in 2 mg, 5 mg, or 10 mg vials. The standard diluent is bacteriostatic water (0.9% benzyl alcohol) for multi-dose handling; sterile water is an option only when the batch will be used within a day or two. Add the diluent slowly down the vial wall and swirl gently. Shaking or foaming can damage the peptide.

For storage, keep lyophilized powder at -20°C long-term; refrigerator temperatures are acceptable for weeks. Once reconstituted, keep the solution refrigerated and use it promptly. The parent peptide degrades extensively within one week in liquid at 4°C or 22°C, remains stable for at least two months at -20°C, and stays detectable in dried matrices ¹⁹. Doping-control laboratories freeze urine specimens for the same stability reason ²⁰.

To work out volumes and doses for a given vial size, use the interactive calculator in this section. Discard any solution that turns cloudy, discolored, or shows particles.

No formal human drug-interaction studies exist for this peptide. What follows is animal, in-vitro, and class-level evidence.

• Hyaluronic acid: additive and studied in the rabbit osteoarthritis model. 0.25 mg AOD9604 plus 6 mg hyaluronic acid outperformed either agent alone ¹⁰.
• Doxorubicin: in-vitro, the fragment enhanced doxorubicin's anti-proliferative effect against MCF-7 breast cancer cells in co-loaded nanoparticles ¹¹. No human data; concurrent chemotherapy should be treated as a monitoring trigger.
• Insulins and insulin secretagogues: mixed in-vitro signals, with potentiated glucose-stimulated insulin release from islets at high glucose ⁹ against reduced glucose uptake in fat cells ⁶. In living animals the net effect was neutral: no hyperglycemia and no insulin-sensitivity impairment ².
• Beta-adrenergic agents: the chronic weight-loss effect depends on beta3-adrenergic receptors ⁴, so non-selective beta-blockers could theoretically blunt the lipolytic response, while beta-agonists could be additive.
• Exogenous growth hormone: no receptor-level interaction, since the fragment does not bind the hGH receptor ³. Lipolytic effects run through separate pathways.
• Corticosteroids: cortisol elevation is a class-level signal for GH-axis peptides ¹⁶, so glucocorticoid co-use may compound insulin resistance.

Common peptide stacks: GLP-1 agonists such as semaglutide or tirzepatide (complementary mechanisms), GH secretagogues such as ipamorelin or CJC-1295 (no receptor overlap but cumulative endocrine risk), and healing peptides such as BPC-157 or GHK-Cu (no mechanistic conflict) ¹⁶. None of these combinations has been studied in trials.

Cycling this peptide is not receptor-reset logic. The fragment does not bind or activate the growth hormone receptor, so the desensitization argument applied to GH secretagogues does not apply here ³. The practical drivers are metabolic and precautionary.

Community patterns: 8-12 weeks on followed by 4 weeks off is the standard; a split-dosing variant runs 4-8 weeks; some run 5 days on and 2 days off for 12 or more weeks. Animal effects appear fast, within 14-19 days ², and community consensus puts the peak fat-loss rate at weeks 4-8, so cycles are typically capped where the response plateaus.

Metabolic hygiene supports scheduled breaks. The fragment reduces glucose uptake in fat cells ⁶ and shifts muscle glycogen synthase toward its inactive form ⁸, so off periods let glucose handling return to baseline.

Community practice looks for these break signals: no measurable body-composition change by weeks 4-6, a plateau after 8-12 weeks, rising fasting glucose, accumulating missed doses on a multi-daily schedule, or refrigeration failure that degrades the solution ¹⁹. Competitive athletes face a different constraint entirely: the peptide is WADA-prohibited and detectable via the parent molecule and its more stable CRSVEGSCG metabolite ¹.

No published data document tachyphylaxis, receptor downregulation, or rebound. Cycling is conservative community convention rather than an evidence-based requirement.

Community stacks pair the fragment with compounds acting through complementary pathways. No trial has studied any combination; these rationales are mechanistic.

• GLP-1 agonists (semaglutide, tirzepatide, liraglutide): appetite and gastric-emptying control on one side, adipose lipolysis and blocked fat synthesis on the other ². Low predicted additive hypoglycemia risk, since the fragment preserved insulin sensitivity in rats ².
• GH secretagogues (ipamorelin, CJC-1295, sermorelin, GHRP-2/6): the fragment appears alongside these in self-administration regimens ¹⁶. No receptor overlap, because AOD9604 does not bind the hGH receptor ³, but shared endocrine risks such as prolactin or cortisol elevation and fluid retention are cumulative ¹⁶.
• Healing peptides (BPC-157, TB-500, GHK-Cu): grouped with these in orthopaedic reviews ¹⁸. No mechanistic conflict and no studied interaction; co-use is common and unvalidated.
• IGF-1 LR3, MGF, or insulin: theoretical overlap on nutrient partitioning and insulin signaling. Because the fragment potentiates glucose-stimulated insulin release ⁹, combining it with exogenous insulin raises an unquantified hypoglycemia risk.
• Intact growth hormone: no receptor interaction ³; combination is redundant for lipolysis.

Not approved by the FDA or any other regulator for any indication ¹⁷. AOD9604 entered legitimate pharmaceutical development as an anti-obesity candidate: phase IIa trials were underway by February 2002 ¹², and it remained catalogued among clinical-stage agents in 2006 ¹³ and in patent reviews through 2012 ¹⁵. No approval ever followed, and the trial results were never published.

Today the peptide circulates only in an unregulated gray market, sold direct to patients as a research compound ¹⁷. It is not scheduled as a controlled substance in the US, but enforcement follows from its unapproved-drug status: US authorities identified it in confiscated vials ¹, and Belgian authorities seized and characterized preparations ²¹.

In sport, WADA prohibits it as a growth hormone fragment, banned in and out of competition ¹. Routine urine screening detects it at 50-500 pg/mL ¹, and the stable metabolite CRSVEGSCG extends the detection window ¹. The peptide does not cross-react with the WADA hGH isoform immunoassay, so isoform testing alone will not flag its use ²².

The defining safety claim is what the fragment does not do: no growth hormone receptor binding, no receptor-driven cell proliferation, and no hyperglycemia or insulin-secretion suppression in mice ³, with preserved insulin sensitivity in rats ².

Injection-site reactions such as redness, itching, and transient swelling are the most consistently reported events across GH-axis peptides in human use ¹⁶. Class-level signals for this family include dysglycemia, fluid retention, endocrine disturbance, and muscle or joint aches ¹⁶; for this fragment those risks are theoretically lower given the absent receptor binding, but fragment-specific human data are absent.

Theoretical concerns include transient post-meal glucose dips from the islet effect ⁹, reduced muscle glycogen synthesis capacity ⁸, and an interaction risk with insulin secretagogues ⁹. The dominant real-world variable is product composition: gray-market vials carry unverified purity and dose ¹⁷.

Long-term human safety, pregnancy, pediatric, and cancer-history data are absent ¹². Liquid solutions degrade within a week at refrigerator or room temperature, so reconstituted product should be used promptly ¹⁹.