Fragment 176-191 vs AOD-9604
HGH Fragment · Modified HGH Fragment
Here is how these two compounds compare, based on published research, not marketing claims.
Fragment 176-191
The parent 16-amino-acid fragment of human growth hormone studied for selective fat breakdown without growth hormone's anabolic effects; primarily animal mechanistic data.
AOD-9604
The engineered analog of fragment 176-191 with an N-terminal tyrosine added for stability; reached Phase 2 trials but did not meet the 2006 to 2007 Phase 2b primary endpoint for weight loss.
Fragment 176-191
17 studies
1 human trials
Not FDA-Approved
AOD-9604
20 studies
2 human trials
Not FDA-Approved
What it does
Fragment 176-191
A 16-amino-acid fragment of human growth hormone (residues 176 through 191) studied in animal models for promoting fat breakdown without the metabolic effects of full-length growth hormone. Originally characterized at Monash University in the 1990s. Limited human trial data exists. Not FDA-approved; sold in research-peptide markets.
AOD-9604
A modified analog of human growth hormone fragment 176-191 with a tyrosine residue added at the N-terminus for proteolytic stability. Developed by Metabolic Pharmaceuticals through Phase 2 trials in the 2000s for obesity. The 2006 to 2007 Phase 2b trial in 536 obese adults did not meet its primary endpoint for weight loss over 12 weeks. Commercial development as a drug was discontinued. The compound received Generally Recognized As Safe (GRAS) status as an ingredient. Not FDA-approved as a drug.
How it works
Fragment 176-191
A 16-amino-acid peptide identical to residues 176 through 191 of the C-terminus of human growth hormone. The proposed mechanism, established primarily in rodent and in vitro models, is selective lipolysis: the fragment promotes the breakdown of stored fat in adipocytes (fat cells) and stimulates hepatic fat oxidation while not engaging the IGF-1 anabolic pathway that full-length growth hormone activates. The molecular target on adipocytes is not fully characterized in published literature.
AOD-9604
A modified version of the human growth hormone 176-191 fragment. The added N-terminal tyrosine residue improves resistance to proteolytic breakdown, extending the compound's stability versus the parent fragment. The proposed mechanism mirrors fragment 176-191: selective adipocyte lipolysis and hepatic fat oxidation without engaging the IGF-1 anabolic pathway. Phase 2 trial data showed measurable lipolytic effects but did not establish clinically meaningful weight loss versus placebo at the doses tested.
How often
Fragment 176-191
Animal study protocols used daily subcutaneous injection over weeks. Published human research is limited; no consensus dosing protocol exists in peer-reviewed literature. Fragment 176-191 is not FDA-approved for any indication; clinical availability does not exist outside of research contexts.
AOD-9604
Phase 2 trial protocols tested both daily oral and daily subcutaneous formulations. The Phase 2b trial used a daily oral formulation over 12 weeks. AOD-9604 is not FDA-approved as a drug for any weight management indication; clinical availability for weight management does not exist.
How strong
Fragment 176-191
Animal studies in obese rodent models showed dose-dependent reductions in body fat and increased fat oxidation over weeks of daily injection. Human data is limited to small early-phase studies; no Phase 3 trials were ever conducted, and no large-population efficacy data exists. The compound's evidence base is many orders of magnitude smaller than current GLP-1 medications.
AOD-9604
Phase 2b trial (2006 to 2007) in 536 obese adults did not meet primary endpoint for weight loss versus placebo over 12 weeks. Smaller earlier Phase 2 trials reported variable lipolytic effects but did not establish a consistent magnitude of weight loss. The compound's evidence base for weight management is far smaller and structurally different from current GLP-1 medications, which have completed Phase 3 programs with double-digit percentage mean weight reductions.
Main tradeoff
Fragment 176-191
Limited human trial evidence is the primary structural limitation. The mechanism is theoretically attractive (selective lipolysis without growth hormone's anabolic or diabetogenic effects), but commercial development was never completed for the parent fragment. The engineered analog AOD-9604 is the more thoroughly studied compound in this class. Compounded versions of fragment 176-191 sold in research-peptide markets are not FDA-regulated and may carry purity, potency, or contamination risks that the FDA-approved supply chain protects against.
AOD-9604
AOD-9604 has the most complete clinical trial program of any peptide in the growth hormone fragment lipolytic class, including a Phase 2b trial that was structurally rigorous. The Phase 2b primary endpoint failure is the structural limitation: the trial did not establish clinically meaningful weight loss at the doses and duration tested. Compounded versions sold in research-peptide markets are not FDA-regulated as drugs. The compound's GRAS status applies to ingredient use, not therapeutic use.
Best for
Fragment 176-191
- Mechanistic research interest in growth hormone fragment lipolytic pathways
- Historical context for the AOD-9604 development arc that grew from this fragment
- Researchers comparing the parent fragment to the engineered AOD-9604 analog
AOD-9604
- Research interest in the GH-fragment lipolytic class development arc
- Understanding why this class did not advance to Phase 3 development for weight management
- Researchers comparing the engineered analog to the parent fragment 176-191
How to choose
A good fit for Fragment 176-191
- Mechanistic research interest in the parent natural fragment (residues 176-191) versus the engineered analog
- Studying the original 1990s lipolytic mechanism research at Monash University
- Comparison of animal models in fragment 176-191 versus AOD-9604 trial outcomes
- Research contexts where the unmodified parent compound is the focus
A good fit for AOD-9604
- Reviewing the most thoroughly studied compound in the GH-fragment lipolytic class
- Understanding the 2006 to 2007 Phase 2b trial outcome and what it indicates about the class
- Studying the development arc that took fragment 176-191 forward into clinical testing
- Research contexts where the engineered analog with stability modifications is the focus
Consider both across time
Fragment 176-191 and AOD-9604 are closely related compounds with the same proposed lipolytic mechanism. The structural difference is the N-terminal tyrosine added to AOD-9604 for proteolytic stability. The evidence difference is more material: AOD-9604 has the completed Phase 2 trial program (including a Phase 2b trial that did not meet primary endpoint); fragment 176-191 has primarily mechanistic animal data with limited human trials. Neither is FDA-approved for weight management. For comparisons against the FDA-approved weight management medications, see Semaglutide vs Tirzepatide.
Dosing should be determined by a qualified physician who can evaluate individual circumstances. PSI does not provide personalized dosing guidance.
Official dosing references
- DailyMed(NIH drug labels)
- ClinicalTrials.gov
- PubMed
For readers who want the biology: here is the pathway each compound uses to signal the body. This section is optional. The comparison above covers the practical differences.
▶See the biology
- Adipocyte (fat cell)
- Adipocyte (fat cell) engages Lipolytic Signaling
- Lipolytic Signaling connects to Fat Mobilization
- Lipolytic Signaling connects to Hepatic Fat Oxidation
- Fat Mobilization connects to Body Fat Reduction (animal models); Hepatic Fat Oxidation connects to Body Fat Reduction (animal models)
- Fat Mobilization connects to Body Fat Reduction (Phase 2 endpoint); Hepatic Fat Oxidation connects to Body Fat Reduction (Phase 2 endpoint)
Fragment 176-191 engages adipocyte lipolytic signaling, leading to fat mobilization and hepatic fat oxidation in animal models.
AOD-9604 engages the same proposed lipolytic mechanism as fragment 176-191, with the engineered N-terminal tyrosine improving proteolytic stability.
Research Evidence
Both compounds sit at PSI's Human Trials tier with limited published evidence. Fragment 176-191 has primarily 1990s mechanistic animal studies showing lipolytic activity in adipocytes plus a small body of human research. AOD-9604 has the more complete clinical trial program: Phase 2 dose-finding studies in the early 2000s plus the structurally rigorous Phase 2b trial in 536 obese adults from 2006 to 2007. The Phase 2b trial did not meet its primary endpoint for weight loss versus placebo over 12 weeks; commercial development as a weight management drug was discontinued thereafter. For research focused on the parent natural fragment, fragment 176-191 is the relevant compound; for research focused on the most thoroughly tested member of the GH-fragment lipolytic class, AOD-9604 is the relevant compound.
- 1.
For fat metabolism research, both target the same pathway.
- 2.
For evidence of clinical efficacy, neither has demonstrated significant weight loss in humans.
- 3.
For stability, AOD-9604's modification may provide better bioavailability.
- 4.
For honest assessment: both remain popular in peptide therapy despite lacking efficacy data.
Key Limitations
- •AOD-9604 failed its pivotal obesity trial.
- •Fragment 176-191 has never reached pivotal clinical trials.
- •The popularity of both compounds in peptide therapy exceeds their evidence base.
- •Comparing two compounds that both lack efficacy data has limited clinical utility.
Community Discussion
PSI monitors discussions across peptide research and biohacking communities. These are reported experiences, not clinical evidence.
Fragment 176-191
"Fragment 176-191 is a cheaper alternative to AOD-9604"
Misleading comparison
"Fragment 176-191 burns fat without side effects"
Insufficient evidence
AOD-9604
"AOD-9604 burns fat without affecting muscle"
Plausible but modest effect
"AOD-9604 helps with joint pain too"
Insufficient evidence
Safety Comparison
Both compounds have limited safety data relative to FDA-approved weight management medications. Fragment 176-191 has limited human safety data; the Phase 2 program for AOD-9604 generated more substantial safety data, with no major safety signals reported in the published trials, though the Phase 2b primary endpoint failure for efficacy structurally limits the trial program's scope. Neither compound has long-term post-marketing surveillance data of the kind available for semaglutide and tirzepatide. Compounded versions of either peptide sold in research-peptide markets are not FDA-regulated as drugs and may carry purity, potency, or contamination risks that the FDA-approved supply chain protects against.
Fragment 176-191
Very limited safety data. Theoretical safety profile is favorable since it lacks the growth-promoting effects of full HGH.
AOD-9604
Phase IIb trial showed no serious safety concerns. Generally well-tolerated but efficacy was not demonstrated.
What the Research Suggests
These are essentially the same compound with a minor structural modification. Neither has proven effective for weight loss in humans. Their continued popularity is driven by theoretical mechanism and accessibility, not clinical evidence.