Research and laboratory use only. Not for human consumption.
Fragment 176-191
HGH Fragment 176-191 is a synthetic 16-amino-acid peptide corresponding to the final sixteen residues of the 191-residue human growth hormone molecule. It emerged from research investigating whether different regions of growth hormone could produce distinct metabolic effects.
What is HGH Fragment 176-191?
Human growth hormone, also known as somatotropin, is a protein consisting of 191 amino-acid residues. Fragment 176-191 corresponds specifically to the final sixteen residues at the carboxyl, or C-terminal, end of that protein.
Researchers became interested in this region because growth hormone has multiple biological effects, including effects on growth, insulin-like growth factor 1 signalling and lipid metabolism.
Early structure-function experiments investigated whether different parts of the growth hormone molecule carried different biological information.
Synthetic C-terminal fragments, including residues 176-191, were found to produce metabolic effects in animal experiments. This encouraged later development of modified analogues intended to investigate lipid metabolism without reproducing all actions of full-length growth hormone.
The best-known result of that development programme was AOD9604. However, AOD9604 and native HGH Fragment 176-191 are not chemically identical, and their evidence should not be combined.
Why is it called Fragment 176-191?
The name is unusually literal. Fragment 176-191 means that the peptide reproduces amino acids numbered 176 through 191 within the full-length human growth hormone sequence.
Because position 191 is the final residue of human growth hormone, this makes Fragment 176-191 the C-terminal sixteen-amino-acid section of the hormone.
This naming convention is important because other related research compounds cover slightly different regions of the growth hormone molecule or contain structural modifications.
Fragment 176-191 and AOD9604 are not the same molecule
This is the most important distinction on the page. Most of the human clinical evidence commonly quoted for “HGH Frag” actually involves AOD9604 rather than the native 176-191 fragment.
Fragment 176-191
Corresponds directly to amino-acid residues 176 through 191 of human growth hormone.
The native first residue is phenylalanine — F.
AOD9604
AOD9604 is commonly described as Tyr-hGH177-191 — a modified peptide based on residues 177-191 with an N-terminal tyrosine.
This is the compound that underwent the major human obesity development programme.
Human safety or efficacy findings from AOD9604 cannot automatically be used to establish the safety, pharmacokinetics or therapeutic effectiveness of native HGH Fragment 176-191.
Amino-acid sequence & molecular structure
Native HGH Fragment 176-191 contains sixteen amino-acid residues and retains the two cysteine residues present in this region of human growth hormone.
Why are researchers interested in this fragment?
Research began as an attempt to understand which structural regions of growth hormone were responsible for its different metabolic activities.
Lipid Metabolism
The C-terminal region of growth hormone became associated with experimental effects on fat metabolism and therefore attracted interest in obesity research.
Metabolic Signalling
Early C-terminal-fragment experiments investigated effects on glucose, insulin and metabolic physiology in animals.
Obesity Research
Interest in separating growth hormone's metabolic effects from its growth-related actions eventually contributed to development of AOD9604.
Structure–Function Biology
Short fragments allow researchers to investigate which regions of a larger hormone carry specific biological information.
What biological mechanisms have been proposed?
Mechanistic claims surrounding native Fragment 176-191 need caution because much of the modern mechanistic literature involves AOD9604 rather than the native peptide itself.
Lipid Mobilisation
The C-terminal domain of growth hormone has been investigated for effects on triglyceride breakdown and adipose metabolism.
Lipogenesis Research
Related peptide studies examined whether the C-terminal domain could influence storage of lipid within adipose tissue.
Adrenergic Pathways
AOD9604 animal research implicated beta-3 adrenergic signalling in some chronic metabolic effects. This finding cannot automatically be assigned to the native fragment.
GH-Axis Separation
Researchers investigated whether a short C-terminal sequence could reproduce selected metabolic effects without reproducing the full GH–IGF-1 growth pathway.
What could this research eventually contribute to?
These areas describe scientific questions generated by experimental research. They are not established medical uses for Fragment 176-191.
Weight & Adipose-Tissue Research
The principal translational interest in the C-terminal growth-hormone domain has been whether lipid-metabolism signalling could be separated from the broader endocrine effects of full-length growth hormone.
Metabolic Pathway Research
The fragment remains scientifically useful for understanding the relationship between growth hormone structure, adipose biology, glucose regulation and insulin signalling.
Peptide Analogue Development
The development of AOD9604 demonstrates how a native hormone fragment can serve as the starting point for designing a modified experimental compound.
Experimental Drug-Delivery Research
A 2022 laboratory study examined Fragment 176-191 within doxorubicin-loaded chitosan nanoparticles in MCF-7 breast cancer cells. This was an in-vitro drug-delivery experiment and does not establish an anticancer treatment.
Native HGH Fragment 176-191 has not been demonstrated to produce clinically meaningful weight loss, fat loss or other therapeutic effects in humans.
How strong is the evidence?
The evidence becomes substantially weaker once the question changes from general C-terminal hGH biology to effects of native Fragment 176-191 in humans.
Structural Evidence
The peptide's relationship to residues 176-191 of the human growth hormone sequence is clearly defined.
Animal Evidence
Early experiments directly examined synthetic hGH C-terminal fragments in rats and demonstrated metabolic activity.
Human Evidence
Direct clinical evidence for native Fragment 176-191 is essentially absent. AOD9604 trials involve a related but different compound.
Established Medicine
Fragment 176-191 has no established approved therapeutic indication.
Has native Fragment 176-191 been studied in humans?
Clinical results commonly attributed to “HGH Frag” generally come from studies of the modified analogue AOD9604.
The native peptide FLRIVQCRSVEGSCGF does not have a conventional human clinical-development programme supporting therapeutic use.
By contrast, AOD9604 was studied extensively in humans during an obesity development programme conducted between approximately 2001 and 2006.
Those trials evaluated the modified tyrosine-containing peptide YLRIVQCRSVEGSCGF. They therefore cannot establish the human pharmacokinetics, safety or efficacy of the native fragment.
This distinction is particularly important because online summaries frequently describe AOD9604 studies as if they were clinical trials of Fragment 176-191.
What happened to AOD9604?
Although AOD9604 is not the same molecule as Fragment 176-191, its development history helps explain why the growth-hormone C-terminal region became so widely discussed.
AOD9604 human programme
Published safety analysis describes six randomized, double-blind, placebo-controlled human trials involving approximately 893 participants.
The programme examined whether the peptide could produce useful metabolic effects without increasing IGF-1 or reproducing certain adverse metabolic properties of full-length growth hormone.
FDA review material reports that a 536-participant obesity study conducted under late-stage development conditions did not demonstrate the weight loss needed to support the programme's commercial objectives. Those findings concern AOD9604, not native Fragment 176-191.
What don't we know yet?
Factors affecting peptide stability
Fragment 176-191 contains two cysteine residues, making structural state and analytical characterization particularly relevant. Researchers should use compound-specific documentation for the exact material under study.
Temperature
Temperature can influence chemical degradation and long-term peptide stability.
Light
Light exposure may contribute to degradation of susceptible laboratory materials.
Moisture
Moisture can influence peptide integrity and physical stability.
Disulfide State
The two cysteine residues can participate in an intramolecular disulfide bond. Analytical documentation should identify the structural form of the research material.
Preclinical investigational peptide — not an approved medicine
Native HGH Fragment 176-191 has no established approved therapeutic indication and has not undergone the conventional clinical-development programme required to establish efficacy and safety for human treatment.
AOD9604 is a related but chemically distinct analogue. Its human obesity research does not convert native Fragment 176-191 into a clinically validated compound.
ASA Research Labs provides this information for scientific and educational purposes only. Nothing on this page should be interpreted as medical advice, dosing guidance or a recommendation for human use.
Selected scientific references
References are listed without external links. ASA distinguishes studies of native hGH C-terminal fragments from studies involving the modified analogue AOD9604.
Scientific research information only
This profile is provided for scientific and educational information. HGH Fragment 176-191 is an investigational research compound and is not presented by ASA Research Labs as an approved weight-loss medicine, obesity treatment or therapy for any human condition. Discussion of lipid metabolism, animal research, AOD9604 clinical trials or potential applications does not establish safety or efficacy of native Fragment 176-191 in humans. This page does not provide instructions for administration, dosing or human use.