# HGH Fragment 176-191: Evidence, Mechanism & Legal Status

> A clinical monograph on HGH Fragment 176-191 — the C-terminal 'lipolytic tail' of growth hormone sold as a fat-loss peptide. No human RCTs, an antilipogenic animal mechanism, and a closely related analogue (AOD-9604) that failed its pivotal obesity trial.

*Published 2026-06-30 · Updated 2026-07-01 · By Marcus Feld, PharmD, BCPS*

The short answer
HGH Fragment 176-191 is a synthetic copy of growth hormone's C-terminal 'lipolytic tail,' marketed as a fat-loss injectable. But **no human randomized controlled trial of the unmodified fragment exists**, the original primary literature found it to be *antilipogenic* (it blocks new fat synthesis) rather than overtly fat-burning, and the closest human evidence belongs to a *different* molecule — the analogue AOD-9604, which **failed** its pivotal weight-loss trial. Highest evidence grade: **C (preclinical only)**. It is not FDA-approved and is prohibited in sport at all times under WADA.[1](https://peptidevox.com/#r1)[6](https://peptidevox.com/#r6)[11](https://peptidevox.com/#r11)

HGH Fragment 176-191 (often given in the laboratory as the 177-191 peptide) is the carboxy-terminal region of human growth hormone, sold by peptide vendors as a fat-loss compound. Its popularity in physique and weight-loss circles is large; its proof in humans is essentially absent. This monograph separates the genuine, modest animal biology from the marketing.[1](https://peptidevox.com/#r1)

*This article is informational and editorial content for research and educational purposes only. It is not medical advice, not a protocol to follow, and not a sourcing guide. HGH Fragment 176-191 is not an FDA-approved drug; it is sold as a "research chemical not for human use" and is prohibited in sport. Dosing figures are reported strictly as seen in the published literature for completeness — not as recommendations. Consult a licensed clinician before any health decision.*

## What is HGH Fragment 176-191 and how does it work?

Human growth hormone is a 191-amino-acid protein whose growth-promoting (somatogenic/IGF-1) activity and metabolic (lipid) activity map to different regions of the molecule — a structure-function separation recognized since the 1970s.[2](https://peptidevox.com/#r2) The lipid-active domain sits at the C-terminus. In the foundational synthetic-peptide work the active sequence is given as hGH 177-191 (Leu-Arg-Ile-Val-Gln-Cys-Arg-Val-Ser-Glu-Gly-Ser-Cys-Gly-Phe); the commercially sold "176-191" peptide is the same region, with numbering conventions differing by one residue.[1](https://peptidevox.com/#r1) It contains two cysteines that form an intramolecular disulfide loop, and reducing that bond markedly diminishes activity, indicating the loop is structurally required.[4](https://peptidevox.com/#r4)

The mechanism — all of it preclinical — does **not** involve the classical GH receptor. The fragment and its analogue do not compete with hGH for GHR binding and do not raise IGF-1.[5](https://peptidevox.com/#r5) The leading hypothesis is β3-adrenergic-receptor (β3-AR) dependent. In the pivotal mechanistic study, both intact hGH and AOD-9604 restored the suppressed β3-AR messenger RNA of obese mice toward lean-control levels, and the metabolic effects (increased energy expenditure, fat oxidation, decreased body-weight gain) were abolished in β3-AR knockout mice — the receptor is required for the response.[5](https://peptidevox.com/#r5) At the enzyme level, the C-terminal domain stimulated hormone-sensitive lipase and inhibited acetyl-CoA carboxylase (a lipogenic enzyme) in isolated rat adipose tissue.[4](https://peptidevox.com/#r4) No validated half-life is published for the unmodified fragment; small unmodified peptides of this size are expected to be cleared within minutes, which is part of why the stabilized AOD-9604 was developed.[6](https://peptidevox.com/#r6)

Fragment vs analogue — the single most important distinction
Scientists at Metabolic Pharmaceuticals added a tyrosine residue to the fragment's N-terminus to create **AOD-9604**, a chemically distinct 16-mer. Nearly all human data — and the strongest β3-receptor work — used AOD-9604, *not* the "HGH Frag 176-191" sold online. Treating them as the same molecule is the most common error in lay write-ups.[6](https://peptidevox.com/#r6)[7](https://peptidevox.com/#r7)

## What is the evidence by indication?

There are no human RCTs of HGH Fragment 176-191 itself for any use; the table below grades the fragment's evidence honestly, and separates it from the analogue's human data.

  HGH Fragment 176-191 evidence by indication

    IndicationBest evidenceGrade

    Fat loss / obesity (the fragment)Rat fat-pad & obese-mouse models: inhibits lipogenesis, reduces body-weight gain & adipose mass; no human RCTC (preclinical)
    Fat loss / obesity (analogue AOD-9604)Six placebo-controlled human RCTs (~893 people): very safe but failed pivotal 24-week weight-loss endpointB human safety / negative efficacy
    Osteoarthritis / cartilageMechanistic/animal discussion only; no adequate controlled human trialD
    Anti-aging, muscle preservation, sleepMarketing extrapolation from GH biology; no human evidenceD

What the animal work actually showed for the fragment: in isolated rat adipose tissue the synthetic C-terminal sequence reproduced hGH's antilipogenic action but showed *no significant lipolytic effect* (no increase in glycerol release).[1](https://peptidevox.com/#r1) Chronic treatment of obese (ob/ob) mice with hGH 177-191 reduced cumulative body-weight gain and adipose-tissue mass and significantly inhibited lipogenesis.[3](https://peptidevox.com/#r3) The domain (as AOD9401/AOD9604) reduced adipocyte diameter in obese Zucker rats without inducing insulin resistance or glucose intolerance.[4](https://peptidevox.com/#r4) The fairest reading is that the dominant, most reproducible action of this domain is inhibition of *making* new fat, with lipolytic/β3-mediated effects shown chiefly for the stabilized analogue in animals.[5](https://peptidevox.com/#r5)

What the human trials of AOD-9604 (the analogue) showed: across six randomized, double-blind, placebo-controlled trials in roughly 893 participants the compound was very safe, but the program did not deliver clinically meaningful weight loss.[6](https://peptidevox.com/#r6) An earlier ~12-week study reported a modest signal (about 2.6 kg loss versus 0.8 kg placebo at the favorable dose), but the pivotal 24-week Phase 2b trial in 502 obese adults failed its primary weight-loss endpoint versus placebo, and obesity development was discontinued in 2007. The negative pivotal result was never published as a standalone peer-reviewed efficacy paper — itself a red flag. For the unmodified fragment, human efficacy is unproven (Grade C); for the analogue with the best human data, efficacy is essentially null. The 2026 WADA Prohibited List is published at [wada-ama.org](https://www.wada-ama.org/en/prohibited-list) for readers who want the primary anti-doping text.[11](https://peptidevox.com/#r11)

## What doses appear in the literature?

Reported strictly as information, not a protocol. No controlled human trial validated any dose or route of the unmodified fragment, so there is no manufacturer prescribing information, no validated concentration, and no quality assurance on research-grade material.[6](https://peptidevox.com/#r6) The published human program studied the analogue AOD-9604 by intravenous (25-400 µg/kg single doses) and oral routes (0.25 mg up to 54 mg); notably, subcutaneous injection was *not* among the routes in that published human program.[6](https://peptidevox.com/#r6) By contrast, real-world anecdotal "HGH Frag" use is almost universally subcutaneous, with online and clinical-use write-ups commonly describing about 250-500 mcg per dose, sometimes split into a morning and pre/post-exercise dose on an empty stomach — these figures are conventional lore, not trial-derived, and are reported here only for completeness.[6](https://peptidevox.com/#r6) Oral bioavailability of the AOD-9604 hexadecapeptide was low in human studies, and the higher oral doses drove most of the GI adverse events.[6](https://peptidevox.com/#r6)

## How safe is HGH Fragment 176-191?

Human adverse-event data come from the AOD-9604 program — the only sizeable human dataset, and a different molecule. AOD-9604 showed a safety and tolerability profile indistinguishable from placebo, with no treatment-related serious adverse events across all six trials.[6](https://peptidevox.com/#r6) In IV studies headache was the dominant complaint (mild-to-moderate in up to about 70% in one obese-male study), with transient mild euphoria in a minority. Oral studies showed dose-related GI effects — diarrhea, flatulence, nausea, increased appetite — most prominent at 54 mg. Reassuringly there was no IGF-1 elevation, no glucose intolerance, no insulin resistance, and no anti-drug antibodies detected up to 24 weeks — mechanistically expected because the fragment cannot dimerize the GH receptor.[6](https://peptidevox.com/#r6)

The dominant theoretical concern is the GH-axis-adjacent tumor/proliferation caution in anyone with active or prior malignancy; the reassuring counterpoint is that the fragment and AOD-9604 do not raise IGF-1 and do not bind the GH receptor, which removes the principal IGF-1-mediated proliferative pathway — though long-term human oncologic data are absent.[5](https://peptidevox.com/#r5) In practice the largest real-world hazard is product quality: unapproved "research" peptides carry risks of mislabeling, under- or over-dosing, endotoxin or microbial contamination, and unverified identity — none captured by the clean clinical-trial record of pharmaceutical-grade AOD-9604.[7](https://peptidevox.com/#r7) Pregnancy, breastfeeding, and pediatric use are precautionary contraindications because no data exist.

## What is the FDA and WADA status in 2026?

Neither HGH Fragment 176-191 nor AOD-9604 is FDA-approved for any indication; there is no NDA or BLA, and the molecule never cleared Phase 3 (obesity development ended in 2007).[6](https://peptidevox.com/#r6) On compounding, AOD-9604 (free base and acetate) was nominated for the 503A bulks list for weight loss, osteoporosis and osteoarthritis; the original nominations were withdrawn, and the FDA continued evaluation on its own initiative, noting there is no USP monograph for the substance.[7](https://peptidevox.com/#r7) The FDA's Pharmacy Compounding Advisory Committee evaluated AOD-9604 at its December 2024 meeting, and the agency's analysis weighed the bulks-list criteria against inclusion, with the substance not placed on the 503A bulks list.[8](https://peptidevox.com/#r8)[9](https://peptidevox.com/#r9) Under the finalized interim policy (January 7, 2025) the FDA also stated it does not intend to add newly nominated substances to the interim framework.[10](https://peptidevox.com/#r10) The practical effect: AOD-9604/hGH-fragment compounding has no clear lawful path under 503A, and the unmodified fragment likewise lacks any approved or sanctioned status — it is sold only as a "research chemical, not for human use."

For athletes the picture is unambiguous. The compound is prohibited at all times — in and out of competition — under Section S2.2.3 (growth hormone, its fragments and analogues), and the WADA Prohibited List names "growth hormone fragments, e.g. AOD-9604 and hGH 176-191" as explicit examples.[11](https://peptidevox.com/#r11) No automatic Therapeutic Use Exemption applies, and athletes face sanction for use.[12](https://peptidevox.com/#r12) It is not a DEA-controlled substance, but non-scheduling does not make non-research human use lawful.

**Bottom line.** HGH Fragment 176-191 has a genuine but modest metabolic biology — in animals and isolated fat cells the C-terminal domain inhibits lipogenesis and (as the stabilized analogue AOD-9604) activates hormone-sensitive lipase through a β3-adrenergic pathway, without raising IGF-1. But its billing as a "proven fat-loss peptide" is not supported by human evidence: there are zero human RCTs of the fragment, the strongest human data belong to a different molecule that failed its pivotal weight-loss trial, there is no validated dose or route, and it is banned in sport. The proven mechanism is interesting; the human clinical promise is, at best, unrealized and, at worst, contradicted by the best available trial. Regulatory facts here are current as of June 2026 and should be re-verified for later anti-doping and compounding updates.

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Source: https://peptidevox.com/peptide-encyclopedia/hgh-fragment-176-191
Index: https://peptidevox.com/llms.txt · Full text: https://peptidevox.com/llms-full.txt