What is HGH Fragment 176-191?

What sources report

Human growth hormone is a chain of 191 amino acids.⁹ HGH Fragment 176-191 is a synthetic copy of the last 16 of them, FLRIVQCRSVEGSCGF, which match the tail of the natural hormone's reference sequence.¹² A disulfide bond between its two cysteines closes the chain into a loop.¹ Synthetic tail pieces of growth hormone, 176-191 among them, were tested in rats as early as 1978.²⁰

The name is used loosely. AOD-9604, the version tested in people, is hGH 177-191 with an extra tyrosine at the front, so it differs from the native fragment by one amino acid.⁶¹⁵ Some sources even apply the fragment's name to AOD-9604: a 2026 review says it is sometimes labeled hGH 176-191.⁷ The supplier listing behind the HGH Fragment 176-191 for sale page gives the tyrosine-first sequence, and that page sets it against PubChem's records.¹²

Animal and tissue studies

Three patterns stand out. The weight effects were reported in obese animals.³¹⁹ The AOD versions did not show the blood-sugar rise reported for the native fragment in 1978.²⁰⁴¹⁹ And the mechanism is unsettled: AOD-9604 did not compete for the growth hormone receptor in cell tests, and FDA's 2024 review concluded that its molecular target is unknown.¹⁹⁶

Human studies

A ClinicalTrials.gov search for 176-191, HGH fragment, growth hormone fragment and AOD-9604 returned no studies in October 2026.⁵ All the human data found come from AOD-9604.¹³ Its developer, Metabolic Pharmaceuticals, funded six randomized, placebo-controlled trials in 893 adults from 2001 to 2006, with the peptide given by vein or by mouth.¹³

A safety summary by authors tied to the developer reported side effects similar to placebo, no change in IGF-1 or glucose tolerance, and no antibodies to the peptide.¹³ Efficacy did not hold up: the largest trial gave AOD-9604 or placebo by mouth to 502 randomized adults on diet and exercise, and found no significant difference in weight loss at its 12-week primary endpoint.⁶⁷ Development for obesity stopped, and FDA says the trial does not appear to have been published.⁶ A 2026 review calls the human evidence limited and largely short-term.⁷

Trial-by-trial detail: What is AOD-9604?. Other compounds researched for weight are compared in Peptides and weight loss.

Other research

A 2022 drug-delivery study loaded chitosan nanoparticles with both the fragment and the cancer drug doxorubicin.²⁵ Against MCF-7 breast cancer cells in the lab, the dual-loaded particles slowed growth more than particles carrying doxorubicin alone.²⁵

How it differs from related compounds

• Growth hormone (somatropin): the full hormone, approved as a prescription drug.⁹ Its label warns that somatropin may decrease insulin sensitivity,⁹ while AOD-9604 trials found no change in glucose tolerance.¹³ See What is HGH?
• Tesamorelin: a growth hormone-releasing factor analog, first approved in 2010 for reducing excess belly fat in adults with HIV and lipodystrophy.²⁶ The label says it is not indicated for weight-loss management because its effect on weight is neutral.²⁶ See What is Tesamorelin?
• CJC-1295 and ipamorelin: WADA lists both under S2.2.4, growth hormone releasing factors, a separate subsection from the fragments in S2.2.3.⁸ See What is CJC-1295 + Ipamorelin?

Side effects

No human side-effect data were found for hGH 176-191 itself.⁵¹³ The list draws on AOD-9604 trials, animal work and FDA's reviews. Trial-by-trial detail: AOD-9604 side effects.

Common in AOD-9604 trials

• Headache was the most frequent adverse event: 42.6% of participants in the 12-week trial, where adverse events overall were spread similarly across the AOD-9604 groups and placebo.¹³
• At 54 mg by mouth daily for 7 days, the highest oral dose tested, headache, diarrhea and flatulence were more frequent.¹³
• In a single-dose IV study in 23 obese men, 5 reported mild or moderate euphoria during AOD-9604 periods and none during placebo.¹³
• In an IV dose-escalation study of 15 men, there was one case each of injection-site bruising, injection-site pain and application-site reaction.¹³

Serious events

• In the 12-week trial, 5 of 250 people on AOD-9604 had serious events: basal cell carcinoma, squamous cell carcinoma and a lipoma (20 mg group), breast cancer (5 mg group) and melanoma (10 mg group).¹³ The investigator judged none related.¹³
• In the 23-man IV study, one severe episode of chest tightness was judged possibly related to AOD-9604.¹³
• In the 24-week trial, 18 people (3.6%) had one or more serious adverse events, distributed similarly across placebo and the three AOD-9604 doses.¹³

Warnings

• FDA warns that compounded AOD-9604 may pose a significant risk of immunogenicity, an unwanted immune response, with possible impurity and characterization problems.²⁷ It says injectable routes may present a particular risk.⁶
• FDA reports serious adverse events possibly linked to AOD-9604, says it cannot tell whether the peptide caused them, and says it lacks the information to judge whether it would harm people.²⁷
• In animal toxicology reviewed by FDA, rats dosed by mouth for 6 months showed osteocalcin (bone marker) changes that appeared dose- and time-dependent, and female monkeys dosed by mouth for 9 months showed liver-cell vacuolation that appeared to rise with dose. FDA said positive genotoxicity signals could not be dismissed.⁶
• In a 1978 rat study, the native fragment raised blood glucose briefly and insulin for longer, and a 1982 study tied related tail peptides to insulin resistance.²⁰²¹
• Reactions to injection under the skin are undocumented: FDA found no human data for that route.⁶
• A 2026 review says the largely unregulated peptide supply chain often sells mislabeled or contaminated products.¹¹
• Pregnancy and breastfeeding: no human data were found, and FDA found no reproductive or developmental toxicity studies.⁶

Dosage information

No human dose of hGH 176-191 has been established, and ClinicalTrials.gov lists no human trial of it.⁵¹³ The doses below come from published animal studies and AOD-9604 trials, and they are not guidance for people.

FDA found no human data for AOD-9604 given by injection under the skin or applied to the skin.⁶ A 2026 review notes that daily injection regimens circulate on bodybuilding forums, and says such online protocols must not be interpreted as clinically validated or safe.⁷ Study-by-study notes for the tyrosine version: AOD-9604 dosage.

Reconstitution and storage

The vial holds 2 mg of white freeze-dried solid, and no diluent comes with it.¹² The supplier lists 36 months at -20 °C or 30 days at 2 to 8 °C, without saying whether the 30 days applies to the powder or the solution, and asks for refrigeration once mixed.¹² These are supplier statements, not published stability data.

Published handling data come from AOD-9604. In its IV trials, the freeze-dried study drug was mixed with sterile water for injection before use.¹³ For the acetate form of AOD-9604, FDA cites supplier documents that give -20 °C for storage, with stability reported beyond four years, and 2 to 8 °C only for periods under six months.⁶ FDA adds that peptides like it are sensitive to pH and heat: the disulfide bridge can break down, and the chains can form aggregates that may lose activity.⁶

The same pattern shows in stored blood: hGH 176-191 was extensively degraded after one week in serum or plasma kept at 4 °C or 22 °C, yet stable for two months or more at -20 °C.¹⁸ No published data were found on how the fragment holds up after mixing with bacteriostatic water.

General lab technique is set out in How to reconstitute a peptide vial, and the same steps for the tyrosine version, with its published figures, are in How to reconstitute AOD-9604. The reconstitution calculator does the concentration math, and How to store peptides covers temperatures.

Regulatory status

United States. hGH 176-191 is not an approved drug.⁶⁷ It does not appear on FDA's list of bulk substances nominated for 503A pharmacy compounding (updated May 14, 2026), so FDA is not evaluating it for that list.¹⁴ For AOD-9604, FDA's 2024 review judged the evidence that it works for obesity, by any route, to be lacking.⁶ FDA's Pharmacy Compounding Advisory Committee then voted 12 to 0, on December 4, 2024, against putting AOD-9604 on the 503A list.¹⁷ FDA's safety-risks page names AOD-9604 among withdrawn nominations and warns of immune reactions and impurities; hGH 176-191 is not named there.²⁷

Enforcement. A full-text search of FDA's warning letter database for 176-191 returned no letters in October 2026.²⁸ In an August 24, 2026 warning letter to a research-peptide seller, FDA said 'for research use only' labels did not change its finding that the products were drugs for human use.²⁹ The letter added that marketing bacteriostatic water for reconstitution provided the means to prepare an injectable drug for human administration.²⁹

Sport. hGH 176-191 is a named example in section S2.2.3, growth hormone fragments, of WADA's 2026 Prohibited List, so it is banned in and out of competition.⁸ FDA's 2024 review notes that AOD-9604 has been used in sport as a doping agent.⁶ A 2015 paper from a US anti-doping laboratory reports AOD9604 in confiscated vials and describes a urine test that detects it down to 50 pg/mL.³⁰