HGH Fragment 176-191 Peptide Research and Procurement Guide

HGH Fragment 176-191 is a 16-amino acid C-terminal peptide derived from the tail end of human growth hormone. Also referred to as hgh fragment 176 191 in compound registries and supplier documentation, it was isolated specifically because it carries the lipolytic signaling properties of full-length hGH without the broad systemic effects that make the parent hormone difficult to study in isolation. That structural specificity is what keeps it on procurement lists across pre-clinical labs and research programs focused on adipose metabolism.

The grey-market peptide space is noisy. Most vendors carry the compound; very few explain what the science actually says about it, where the evidence ends, or what a legitimate COA looks like before you place an order. This guide covers all of that: the biochemistry, the pre-clinical data, the safety profile, handling basics for lab use, and the sourcing criteria that separate credible suppliers from ones worth avoiding. This is a research-first guide, not a dosing protocol or medical recommendation.

What HGH Fragment 176-191 Actually Is

The peptide’s full primary sequence reads: Tyr-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe, or YLRIVQCRSVEGSCGF in single-letter notation. It represents amino acids 176 through 191 of the 191-amino acid human growth hormone protein. The two cysteine residues at positions 7 and 14 of the fragment form a disulfide bridge that constrains the peptide’s three-dimensional shape and contributes to its stability. The N-terminal tyrosine substitution in the synthetic version improves chemical stability compared to the native, unmodified fragment.

The molecular weight sits at approximately 1,817 g/mol, CAS number 221231-10-3, and the compound is supplied as a lyophilized powder soluble in bacteriostatic water. These are the identifiers you should confirm against a COA before sourcing.

Full-length hGH is a 191-amino acid hormone with broad systemic reach: it stimulates IGF-1 production, influences glucose metabolism, and drives anabolic activity across multiple tissue types. Pre-clinical studies indicate that the C-terminal fragment does not appear to significantly activate GH receptor-mediated IGF-1 or anabolic pathways. It does not bind the growth hormone receptor, and available evidence suggests it does not trigger the IGF-1 elevation or insulin-related effects associated with the parent molecule, though some older animal studies have noted transient glucose and insulin changes at specific doses. Isolating this separation of function is the core scientific rationale for studying the fragment independently.

The Lipolytic Mechanism: How Frag 176-191 Targets Fat Cells

cAMP/PKA Signaling Pathway

Preclinical data indicate that the compound acts as a beta-3 adrenergic receptor (ADRB3) mimetic in adipose tissue, with some effects shown to be abolished in β3-AR knockout mouse models. When it binds to ADRB3 on adipocytes, the receptor couples to a stimulatory G protein (Gαs), which activates adenylyl cyclase and increases intracellular cyclic AMP. That cAMP elevation drives everything downstream. Mechanistic details are discussed in a Journal of Clinical Investigation article.

Elevated cAMP activates protein kinase A (PKA), which then phosphorylates hormone-sensitive lipase (HSL) and perilipin, clearing the way for adipose triglyceride lipase (ATGL) to access stored fat. The combined activation of HSL and ATGL breaks stored triglycerides down into free fatty acids and glycerol, which are released from the cell. This is the same core pathway triggered by catecholamines via beta-3 adrenergic stimulation during exercise or fasting, but Frag 176-191 engages it without requiring systemic catecholamine release.

The compound’s effects in pre-clinical models extend beyond active fat breakdown. Research also indicates antilipogenic activity, inhibition of new fat formation from non-fat precursors at the adipocyte level. This dual action distinguishes the fragment mechanistically from general lipolytic compounds that only accelerate breakdown without suppressing new fat synthesis. Unlike full-length hGH, the fragment does not appear to significantly affect insulin sensitivity or glucose metabolism through the same direct pathway, which contributes to its comparatively clean pre-clinical safety profile.

What Pre-Clinical Studies Actually Show About Fat Loss

Animal Model Data

The strongest evidence base comes from obese mouse models. C-terminal hGH fragments, including 176-191 analogs, reduced weight gain, promoted fat oxidation, and demonstrated lipolysis via beta-3 adrenergic pathways in multiple rodent studies. Compared to full-length hGH in the same animal models, the fragment produced fat metabolism signals without the accompanying IGF-1 elevation, glucose intolerance risk, or anabolic side effects. That cleaner profile in obese rodents is the core pre-clinical finding in this compound class.

The comparison to its modified analog AOD-9604 is worth understanding. AOD-9604 adds an N-terminal tyrosine to improve stability and extend the half-life in vivo. In obese animal models, AOD-9604 generally shows higher potency and more consistent results due to those structural modifications. The mechanisms are nearly identical: both act through beta-3 adrenergic upregulation and cAMP-driven lipolysis, both avoid the growth hormone receptor, and both lack IGF-1 or glucose-related side effects in pre-clinical settings. HGH Fragment 176-191 is the foundational analog; AOD-9604 is the optimized version developed from it. Clinical and review literature on AOD-9604 and related compounds is available in open-access repositories for those cross-checking translational claims, see an open-access review.

The Human Data Gap

As of 2026, no controlled human clinical trials on unmodified HGH Fragment 176-191 have been published. The “human use” data sometimes attributed to this compound actually comes from AOD-9604 clinical trials, which showed acceptable safety and tolerability but inconsistent weight-loss results before development was discontinued. Researchers should treat all Frag 176-191 evidence as pre-clinical only and not extrapolate human efficacy from rodent data.

Safety Profile and Regulatory Standing in 2026

Human Trial Summary

Dose-escalation trials conducted on healthy male subjects showed adverse events at rates comparable to placebo in lower-dose conditions. The most common reports were mild injection site reactions, abdominal discomfort, and anorexia. No significant changes in glucose, IGF-1, vital signs, or ECG parameters were recorded in short-term studies. That distinguishes the fragment’s short-term profile favorably from full-length hGH, which carries well-documented risks including glucose intolerance, fluid retention, and joint pain. Note that these figures are derived from AOD-9604 dose-escalation data, as no equivalent trials exist for the unmodified fragment; researchers should consult the original trial reports for precise adverse event counts and subject numbers.

Higher-dose trials showed a different picture. Approximately 69.6% of subjects reported adverse events at elevated doses, with mild to moderate headaches, chest tightness, and mild euphoria among the most noted effects. This dose-dependent shift in tolerability is relevant for any lab designing a study protocol. Long-term human safety data does not exist for this compound; short-term tolerability data should not be read as a clean long-term safety record.

Regulatory Position

The regulatory position is consistent across every major research jurisdiction as of 2026, though nuances exist between agencies. HGH Fragment 176-191 is not approved as a drug, not authorized for compounding, and not cleared for human use in the US, UK, EU, Canada, or Australia. In the United States, it occupies a research-use-only (RUO) framing standard for grey-market peptides operating outside FDA-approved pathways. The compound is not explicitly named on the FDA’s Category 1 compounding list; the closely related AOD-9604 sits on the agency’s Category 2 “do not compound” list, and HGH Fragment 176-191 is treated in practice as an unapproved research peptide under equivalent restrictions. Researchers sourcing this compound should consult current FDA, MHRA, and EMA guidance directly, and understand that the RUO label describes a legal framing for procurement, not approval for human administration.

Research Concentrations, Reconstitution, and Storage

Standard vial sizes for pre-clinical procurement run 2 mg, 5 mg, and 10 mg per vial. Concentration selection depends on the study protocol and reconstitution target. Labs running repeated assays or high-throughput studies typically source multi-vial formats from wholesale suppliers to maintain consistent lot numbers across experimental runs. Switching lot numbers mid-study introduces variability that complicates data interpretation, so procurement planning matters as much as vial format.

Bacteriostatic water is the standard diluent for reconstituting lyophilized Frag 176-191 vials. Add the diluent slowly using a sterile syringe directed at the inner wall of the vial, then roll gently rather than shaking to dissolve the powder without disrupting the disulfide bridge structure. Vigorous agitation can denature the peptide. Once reconstituted, store the solution at 2, 8°C and use within 28 days. If sterile water without benzyl alcohol is used as the diluent, that window drops to 72 hours.

For long-term storage, keep lyophilized vials at -20°C in a dark, dry environment with intact seals. The peptide contains tyrosine and phenylalanine residues susceptible to oxidation, making light and air exposure legitimate concerns. Properly stored lyophilized powder holds stability for up to two years. Once reconstituted, do not freeze the solution; repeated freeze-thaw cycles damage the peptide structure. The in-solution half-life of approximately 2, 3 hours is a relevant parameter for timing in animal model administration protocols.

How to Evaluate Vendors and Verify Purity Before Sourcing

COA Tests: HPLC vs. MS

A legitimate COA for HGH Fragment 176-191 requires two non-negotiable tests. The first is reverse-phase HPLC using a C18 column, typically run with a gradient of 0.1% TFA in water and 0.1% TFA in acetonitrile at 214 nm detection. This produces a purity percentage calculated as the area of the main peak divided by total peak area. HPLC tells you how pure the sample is. The second test is mass spectrometry, which compares the observed mass of the compound to the theoretical mass of approximately 1,817 g/mol. MS tells you what the compound actually is. For an example COA report showing both HPLC and MS outputs, see this example COA report. For an accessible methods guide to peptide purity detection by RP-HPLC and mass spectrometry, see MTOZ Biolabs’ detection methods.

Watch for specific red flags when reviewing documentation:

• Purity claims above 99.5% without accompanying MS confirmation
• COAs with no lot number, no traceability information, or no method details
• Missing detection wavelength or column specifications in the HPLC report
• No comparison of observed vs. theoretical mass in the MS data

For an overview of common vendors and product classes in the non-regulated market, see 7 Essential Grey Market Research Peptides.

R-Peptide Supply (Grey Peptide Shop) provides HGH Fragment 176-191 vials with Certificates of Analysis covering HPLC purity data and mass spectrometry identity confirmation. The catalog includes both standard vial formats and multi-vial wholesale bundles suited to labs and resellers running ongoing research protocols. R-Peptide Supply meets the minimum documentation standard this guide defines, making it a viable option for researchers who have evaluated the compound and are ready to procure through a COA-verified supplier.

Putting It Together Before You Source

HGH Fragment 176-191 is a structurally distinct C-terminal peptide with a well-characterized lipolytic mechanism operating through beta-3 adrenergic receptor activation and cAMP-driven lipase activity in adipocytes. Pre-clinical data in rodent models is consistent on fat metabolism effects. The short-term human safety profile drawn from AOD-9604 dose-escalation trials is comparatively modest relative to full-length hGH. The absence of approved human clinical data for the unmodified fragment as of 2026 is a hard line: this compound remains pre-clinical only.

For research labs and procurement teams, the sourcing decision should hinge on COA completeness, not price alone. A low price on a vial with no MS data or missing lot numbers is not a deal, it is an uncontrolled variable introduced into your research. The minimum standard before any purchase is a COA with HPLC purity documentation and mass spectrometry identity confirmation, both tied to a traceable lot number. If comparative studies require full-length HGH, suppliers offer verified products such as Buy HGH 191AA Peptide | 99%+ Purity HGH for Research.

Researchers ready to source Frag 176-191 vials with verified purity documentation should apply those documentation standards consistently across any supplier evaluated. R-Peptide Supply offers the COA coverage and wholesale formats that structured research programs require. Confirm lot traceability, review both HPLC and MS outputs, and align procurement with your institution’s research-use-only policies before placing any order.