Preloaded Autoinjector | HGH Fragment 176-191 | 3ml Pen | 10mg

The HGH fragment 176-191 pen is a preloaded 3ml autoinjector holding the C-terminal growth hormone fragment in solution at 3.33 mg/ml, 10 mg in total, drawn in 0.01 ml graduations of 33.3 µg each. A single Cys182-Cys189 disulfide closes the molecule, and thiol-disulfide exchange in a stored solution produces dimers and open monomers that weigh almost the same as the intact loop.

Specification Table

What Is HGH Fragment 176 191, and Which Molecule Is in the Device?

What is HGH fragment 176 191 has a precise answer and a market answer, and they are two different peptides. Residue 176 of mature human growth hormone is phenylalanine, so the true fragment is FLRIVQCRSVEGSCGF, registered as CAS 66004-57-7.

The sequence sold across this market as fragment 176-191 is YLRIVQCRSVEGSCGF, which carries tyrosine at position one. That molecule is AOD-9604, built by substituting Tyr for Phe176, not by adding a residue to the front of the chain. Counting back from Phe191 in UniProt P01241 gives Thr175, Phe176, Leu177, and the arithmetic is not in dispute. Both peptides are 16 residues long, both close the same Cys182-Cys189 loop, and they differ by a single oxygen atom.

Listings that invite a researcher to buy fragment 176-191 are, in nearly every case, supplying AOD-9604. That is not necessarily a substitution error on the seller’s part, since the two names have been used interchangeably for twenty years, but it decides which literature applies. Every human number attached to this molecule came from the AOD-9604 programme. The peptide with phenylalanine at position one has never been given to a human being.

The consequence for what the HGH fragment 176-191 pen contains is direct: the certificate of analysis sequence, not the product name, says which molecule is dissolved in the cartridge, and a single accurate mass measurement separates them by 16 daltons.

What Changes When the 176-191 Fragment Ships in Solution?

The Cys182-Cys189 disulfide dominates everything that happens to this peptide in water. Above about pH 7 the thiolate concentration rises, thiol-disulfide exchange accelerates, and a stored solution drifts toward a mixture of closed monomer, open monomer and disulfide-linked dimer.

The difficulty is that this mixture is nearly invisible to the usual checks. Reduction of the loop adds 2.02 daltons. Re-oxidation of two open monomers into a dimer restores the same mass per chain. Amino acid analysis returns identical results for all three species. A purity figure from reversed-phase chromatography can look excellent while the fold that carries whatever activity the peptide has is scrambled across a population of forms. Trace metals make it worse by catalysing air oxidation of any liberated thiol, which converts a reversible equilibrium into a covalent product.

Charge decides the second loss route, and this peptide sits in the worst possible place. Two arginines contribute +2, one glutamate and the free C-terminal carboxylate contribute -2, and the free N-terminal amine contributes +1, giving a calculated net charge of only +0.83 at pH 7.0 and an isoelectric point near 7.9. A molecule held at or close to its own pI has minimal electrostatic self-repulsion, which is precisely the condition under which peptides adsorb most readily to interfaces. A formulation buffered anywhere between pH 7 and pH 8 therefore sits at the worst pH for adsorption and at an accelerating pH for disulfide exchange at the same time. Whether this device does is unpublished.

Gln181 deamidates to glutamate and isoglutamate, a slower secondary route worth 0.98 daltons. What the sequence lacks is more helpful than usual: there is no asparagine and no aspartate anywhere in the chain, which removes Asn-Gly, Asp-Gly and Asp-Pro, the three fastest chemical liabilities in peptide formulation, from the list entirely. There is no methionine and no tryptophan.

Light sensitivity is therefore modest rather than absent, and its mechanism is different from the tryptophan-driven case. The cystine bond itself absorbs weakly in the near ultraviolet, and absorbed energy homolyses the S-S bond to give two thiyl radicals, which then drive exactly the scrambling described above (Kerwin and Remmele 2007). Light protection here is a disulfide question, not a chromophore question.

No forced-degradation, photostability or aqueous formulation study of either sequence has been published, so all of this is residue-level inference from Manning et al. 2010. The comparator with a real formulation record is recombinant human growth hormone, supplied either as a lyophilized powder or as a refrigerated surfactant-containing solution, protected from light and never frozen, with its own Cys182-Cys189 bond among the reasons.

Frag 176-191 vs AOD 9604: What Is the Difference?

The frag 176-191 vs aod 9604 comparison reduces to position one and one oxygen atom: phenylalanine in the true growth hormone fragment, tyrosine in AOD-9604, 1799.08 against 1815.08 for the closed-loop forms, under one percent of the total mass.

The universally quoted molecular weight of 1817.1 belongs to neither of the intact molecules. It is AOD-9604’s sequence with the Cys182-Cys189 bond broken, which is to say the reduced, open-chain form. A certificate of analysis reporting 1817.1 as the expected mass is quoting a linear peptide, and if the material really weighs 1817.1 then the loop is open. The four values that actually exist are 1799.08 and 1801.10 for the phenylalanine peptide closed and reduced, and 1815.08 and 1817.10 for the tyrosine peptide closed and reduced.

The difference matters for evidence rather than for chemistry. AOD-9604 has a human dataset; hGH(176-191) has none. PrymaLab lists the tyrosine-substituted peptide separately as an AOD-9604 5mg vial, and the AOD-9604 article covers that compound’s development record in full. Anyone about to buy fragment 176-191 for quantitative work should read the sequence line on the certificate of analysis rather than the name on the label.

Concentration and Increment Arithmetic for the HGH Fragment 176-191 Pen

The HGH fragment 176-191 pen holds 10 mg in 3 ml, which is 3.33 mg/ml and 33.3 µg in every 0.01 ml graduation, and the molar concentration lands between 1.834 and 1.853 mM depending on which of the four molecular forms is actually in the cartridge.

The working is short. 10 mg divided by 3 ml is 3.3333 mg/ml. Divided by 1817.10 for reduced AOD-9604 that is 1.834 mM; by 1815.08 for the closed form, 1.837 mM; by 1799.08 for the closed phenylalanine peptide, 1.853 mM. The spread is about one percent, which makes molarity the reliable figure and identity the fragile one. One 0.01 ml graduation on a U-100 scale carries 33.3 µg, roughly 18.3 nmol; 0.1 ml carries 333 µg, roughly 183 nmol. The peptide calculator reproduces these for any fill.

Against the published human exposures the device is mid-sized. The AOD-9604 intravenous range in phase I was 25 to 400 micrograms per kilogram, and the oral phase IIb programme ran to 54 mg daily. Against those figures a 10 mg cartridge is a small quantity of material, which is the honest scale comparison and the end of what the arithmetic supports. One 0.01 ml graduation works out near 0.48 micrograms per kilogram at 70 kg, about one fifty-second of the lowest intravenous quantity in that programme. Against the cell-culture work the device is large: rodent adipocyte lipolysis assays run in the low micromolar range, and reaching 1 µM from 1.83 mM is an 1,830-fold dilution.

HGH Fragment 176-191 Pen vs Vial: What Does the Format Suit?

The HGH fragment 176-191 pen vs vial question turns on the disulfide. A pen fixes concentration at manufacture and removes reconstitution error, but it also keeps a redox-active loop in water for the whole shelf life, which a dry cake does not.

The format suits work needing many equivalent draws from one lot across weeks, where the alternative is dissolving vials repeatedly and accepting diluent measurement, incomplete dissolution and transfer loss as per-session variables. Those errors bite harder than usual for a peptide sitting at its own isoelectric point, because every transfer is an interface. The preloaded autoinjector category page sets out the general case.

It suits disulfide-sensitive work badly. Where the experiment depends on a closed loop and a monomeric population, the hgh fragment 176-191 solution vs lyophilized comparison favours the dry form, and a vial also allows the buffer pH to be set away from the exchange-accelerating range rather than inherited from an unpublished formulation.

The hgh fragment 176-191 pen or vial decision otherwise follows the general trade-offs in the pen versus vial article. What is specific here is that no stability figure exists for either sequence, so an HGH fragment 176-191 pen used over many weeks runs an uncharacterised redox experiment alongside the intended one.

What the Product Record Does Not State

The product record does not state the sequence, the disulfide state, the excipient system, the solution pH or the fill date, and the first two of those five are unusual requests that matter more here than the routine three.

Ask for the sequence in letters. FLRIV and YLRIV are different molecules with different evidence bases, and only one of them has ever been in a human. Ask separately for the disulfide state, because a certificate can report high chromatographic purity for material that is substantially reduced; the mass tells the story, 1799.08 or 1815.08 for closed, 1801.10 or 1817.10 for open. Ask whether free thiol was measured at release and by what method.

Then the routine gaps. Excipients enter every assay the solution is added to, and a surfactant would change interfacial adsorption, the dominant loss route at this pI. Solution pH sets the exchange rate and the adsorption behaviour together, and the difference between pH 6 and pH 8 is not small for a peptide with one disulfide. All five belong on the certificate of analysis, and the time to ask is before the first quantitative run.

Verifying the Device and Confirming the Contents Are Intact

Inspect the solution against a white background before each draw, but expect less from the look of it than with other peptides. There is no tryptophan here, so the yellow kynurenine signal that marks oxidation elsewhere does not exist; opalescence and particulate are the visible endpoints, and both point at aggregation rather than chemistry.

Ultraviolet absorbance is unusually diagnostic for a different reason. The phenylalanine peptide has no tyrosine and no tryptophan, so it has essentially no measurable absorbance at 280 nm, while AOD-9604’s single tyrosine gives a weak but real band. A cartridge whose contents read as blank at 280 nm and a cartridge that reads weakly are holding different molecules, which makes the spectrophotometer a first-pass identity check as well as a concentration tool.

The disulfide questions need their own measurements. Ellman’s reagent quantifies free thiol and therefore how much of the population has opened. Size exclusion chromatography or non-reducing gel electrophoresis separates dimer from monomer, which reversed-phase chromatography often will not. High-resolution mass spectrometry resolves all four states at once, since the closed and reduced forms differ by 2.02 daltons and the two sequences by 16.

Let the device equilibrate to ambient temperature first, because viscosity at refrigerator temperature costs volume on every stroke. Verify delivered volume gravimetrically once per device, and store at 2-8°C in the dark, never frozen, because pH shift in a freeze concentrate drives thiol-disulfide exchange directly. The storage and stability article covers the general handling case.

What Does the Literature Actually Report?

The literature reports one substantial human dataset, and it belongs to AOD-9604 rather than to the growth hormone fragment itself, and it ends in a failed trial.

Stier, Vos and Kenley 2013 pooled six randomised, double-blind, placebo-controlled studies run between 2001 and 2006 in approximately 893 subjects: METAOD001 as phase I with 15 subjects, METAOD002 to 004 as phase IIa with 23, 17 and 36, then METAOD005 as a 300-subject 12-week phase IIb and METAOD006 as a 502-subject 24-week phase IIb. The pooled record shows no serious adverse events attributed to the compound, no treatment-related withdrawals, headache and gastrointestinal symptoms as the commonest events, no anti-AOD9604 antibodies, no effect on serum IGF-1 and no adverse effect on glucose tolerance. The 12-week study produced a mean difference of roughly 1.8 kg against placebo. The 24-week study did not meet its endpoint and development was terminated in 2007.

The null findings on IGF-1 and glucose have a structural explanation published alongside them: binding site 2 of growth hormone is entirely absent from a 16-residue C-terminal fragment, so receptor dimerisation and the IGF-1 axis cannot be triggered by this molecule. That is a mechanistic argument for why nothing happened, not a benefit.

The animal work is where the lipolytic hypothesis comes from. Ng et al. 2000 characterised the synthetic lipolytic domain metabolically, and Heffernan et al. 2001 reported increased fat oxidation and weight change in obese mice and in beta-3 adrenoceptor knockout mice. No receptor has ever been identified for either peptide. The wider category is covered in PrymaLab’s overview of peptides marketed for fat loss.

What has not been studied is the larger half. There is no controlled human trial of the subcutaneous route for either peptide, and the only human injectable exposure on record is single-dose intravenous. No human pharmacokinetics and no half-life figure has been published, so none appears here, and no human study of any kind exists for the phenylalanine peptide.

What Is the Safety and Regulatory Position?

Neither peptide is approved by FDA, EMA, PMDA Japan, TGA or Health Canada, in any formulation, for any indication, and AOD-9604’s obesity development was terminated in 2007 after the 24-week trial failed.

The compounding position is often reported incorrectly. AOD-9604 was nominated for the FDA 503A bulk drug substances list and the nomination was withdrawn, which places it on the nominated-but-withdrawn list alongside BPC-157, CJC-1295, epitalon, melanotan II and a thymosin beta-4 fragment. Withdrawal is not approval. It is not on the 503A list and it is not in Category 2, so there is no compounding pathway of any kind.

WADA prohibits both at all times as non-specified substances under section S2.2.3, which names “growth hormone fragments, e.g. AOD-9604 and hGH 176-191” explicitly. WADA has separately stated that AOD-9604 has not been approved for therapeutic use by any government health authority in the world. Any claim that this material is not a banned substance is false on the face of the list.

The reported adverse findings are mild to moderate headache and gastrointestinal symptoms across the pooled trials, and the meaningful finding in that programme is the efficacy failure at 24 weeks. Quoting AOD-9604’s human tolerability record as though it applied to hGH(176-191) is the standard error in this market. This is laboratory research supply, and no part of it is offered for administration to a human or an animal.

What Do the HGH Frag 176-191 Fat Metabolism Claims Rest On?

On rodent work, chiefly from one Australian group in the late 1990s and early 2000s. The proposal was that the amino acids 176 to 191 at the C-terminal end of human growth hormone carry the lipolytic activity of the whole hormone without the growth-promoting activity, so a fragment corresponding to that region would act on fat metabolism alone. HGH frag 176-191 is the name that region is sold under. In mice made obese by diet, HGH frag 176-191 reduced body fat and increased fat breakdown markers, and in adipose tissue preparations it raised lipolysis and suppressed lipogenesis.

The beta-3 adrenergic receptor is usually named as the target, and the original work says something more careful than that. Heffernan and colleagues (2001) found that the fragment raised beta-3 adrenergic receptor expression in mice and that its chronic effect on body fat was absent in beta-3 knockout animals, but that acute increases in energy expenditure and fat oxidation persisted without the receptor, and they concluded the lipolytic action is not directly mediated through it. FDA’s own 2024 review of the closely related AOD 9604 states that the molecular target and mechanism remain unknown. Free fatty acids released from stored triglycerides in fat cells are the measured output; what releases them is not settled.

Human clinical trials do exist for the closely related molecule AOD 9604, and they are the most informative data available. The phase 2b study randomised about 500 adults with obesity across three doses over 24 weeks, and the weight loss against placebo at both twelve and twenty-four weeks was too small to reach statistical significance, so the primary endpoint was missed and development was terminated. FDA’s 2024 advisory committee materials describe around 925 patients across six trials between 2001 and 2007 and call the peptide ineffective for weight loss. It was subsequently given conditional GRAS status in 2012 for use in foods and supplements at 1 mg per day, which is what it is today. The hgh fragment 176-191 peptide sold as a research chemical is not identical to AOD 9604, and no trial of the hgh fragment 176-191 peptide itself has been registered anywhere, and the page above sets out the difference, but the human data that exists is discouraging rather than supportive.

What Should Be Read Into the Metabolic Vocabulary?

Less than the marketing suggests. Insulin sensitivity, insulin resistance and blood sugar all appear in descriptions of this fragment, usually with the claim that it improves blood sugar handling without the glucose-raising effect of intact growth hormone. That claim is mechanistically reasonable and clinically untested: no human trial of the 176-191 fragment has measured fasting glucose, HbA1c or an insulin clamp endpoint. Triglycerides and free fatty acids were measured in rodents and in some AOD 9604 work, with modest and inconsistent results, and body composition endpoints in the human trials did not separate from placebo.

Endurance appears in the same lists and has no supporting study at all. No hgh fragment 176-191 peptide trial has measured it in any species. Nor does any claim about lean mass, since the fragment was specifically designed to lack the anabolic portion of the hormone. Research peptides in this class are often sold as a stack with a secretagogue such as ipamorelin or with CJC-1295 no DAC, on the reasoning that one raises growth hormone while the other supplies its fat-directed portion. No published study has tested that combination in any species.

Where Does the Nanoparticle and Oncology Literature Come From?

From a separate line of work that gets mixed into search results and is worth separating out. Several formulation studies have loaded growth hormone fragments into chitosan nanoparticles, a standard mucoadhesive carrier for peptide delivery, and those papers evaluate release kinetics and cytotoxicity rather than metabolic effects. Doxorubicin turns up constantly in that literature because it is the reference cytotoxic drug for nanoparticle studies, and MCF-7 breast cancer cells are the reference cell line. A paper reporting a doxorubicin-loaded carrier tested against that cell line is a drug-delivery paper, and it says nothing about the peptide in this device.

The distinction matters because those titles look like oncology findings when they appear next to a peptide name in a search result. They are formulation chemistry. Nothing in the published record connects this synthetic peptide to any anticancer effect, and no clinical trials of it exist for any indication.

What Does the Format Settle, and What Should the CoA Show?

A vial arrives dry and is reconstituted with bacteriostatic water at the bench, which lets the concentration follow the experiment and keeps the solid stable while it waits. This pen arrives at a fixed 3.33 mg/ml and starts ageing at a fill date the product record does not state. Injection site handling differs too: a cartridge entered through a fresh needle each time is a different contamination profile from a multi-entry vial, though neither is a claim about the compound.

On the certificate, ask that the target sequence is named explicitly, because the human growth hormone fragment 176-191 peptide and AOD 9604 differ by a single N-terminal tyrosine and their masses differ accordingly. Ask for purity by HPLC with the gradient described, an accurate mass, water content and counter-ion percentage. A supplier who cannot say which of the two molecules is in the device cannot be relied on for anything else on the document.

Published Literature

The references below were each traced to a primary source before listing. All concern the compounds or the formulation chemistry; nothing has been published on this delivery format.

1. UniProt Consortium. P01241 (SOMA_HUMAN), Somatotropin. 217-residue precursor, chain 27-217, mature disulfides Cys53-Cys165 and Cys182-Cys189.
2. Ng FM, Sun J, Sharma L, et al. Horm Res. 2000;53(6):274-278. DOI: 10.1159/000053183
3. Heffernan M, Summers RJ, Thorburn A, et al. Endocrinology. 2001;142(12):5182-5189. DOI: 10.1210/endo.142.12.8522
4. Stier H, Vos E, Kenley D. J Endocrinol Metab. 2013;3(1-2):7-15. DOI: 10.4021/jem157w
5. Kerwin BA, Remmele RL. J Pharm Sci. 2007;96(6):1468-1479. DOI: 10.1002/jps.20815
6. Manning MC, Chou DK, Murphy BM, et al. Pharm Res. 2010;27(4):544-575. DOI: 10.1007/s11095-009-0045-6

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