Key facts
- What it is: a 16-amino-acid synthetic peptide copying the C-terminal tail of human growth hormone (Tyr + hGH 177-191), sold online as "hGH fragment 176-191".
- Developer: Metabolic Pharmaceuticals, a Monash University spin-out in Melbourne, later held by Calzada Ltd. Development began in the late 1990s.
- Proposed mechanism: stimulates lipolysis and fat oxidation in adipose tissue without binding the growth hormone receptor, so no IGF-1 rise and no hGH-type glucose effects.
- Approval status: not approved as a drug in the US, EU, UK, or Australia. No Phase 3 was ever completed and no New Drug Application was ever filed.
- Route in the research: the human trials that showed anything used an oral formulation. Nearly all gray-market product today is injectable.
- Evidence level: strong, replicated rodent lipolysis data; six human trials with no reproducible clinically meaningful weight loss.
- Legal and sport: FDA advisory committee voted 0-12 against a compounding pathway in December 2024; prohibited at all times under WADA section S2 as a growth hormone fragment.
What is AOD9604?
AOD9604 stands for "anti-obesity drug 9604". It is a synthetic 16-amino-acid peptide that copies the far end of the human growth hormone molecule — residues 177 to 191 — with an extra tyrosine attached at the N-terminus to make the sequence easier to synthesize and radiolabel.
Online it is almost always sold as hGH fragment 176-191. The two names get used interchangeably, but they are not chemically identical: the bare 176-191 fragment lacks the added tyrosine. That distinction matters less for biology than it does for buying, because a vial labeled one way may contain the other, or something else entirely.
The idea behind it was genuinely clever. Human growth hormone reduces fat mass, but it also raises blood glucose, drives IGF-1, and promotes cell proliferation — which is why it is a prescription drug with a narrow set of indications and not a fat-loss tool. Researchers at Monash University in Melbourne, working through the spin-out Metabolic Pharmaceuticals, asked whether the lipolytic activity of hGH lives in one small stretch of the molecule. If so, you could isolate that stretch and leave the metabolic baggage behind. AOD9604 was the lead compound from that program, and by the mid-2000s it was one of the most-watched obesity candidates in the pipeline (PubMed 15134286).
Unlike the growth-hormone secretagogues people often mention in the same breath — ipamorelin and CJC-1295 — AOD9604 does not act upstream on the pituitary. It is not designed to make your body release more growth hormone. It is designed to reproduce one downstream effect of growth hormone directly at the fat cell.
How AOD9604 is supposed to work
Peptides are short chains of amino acids that act as signaling molecules, and their activity depends entirely on shape and receptor fit (PubMed 32965931). The core claim for AOD9604 is that it hits the fat-mobilizing part of the growth hormone signal without touching the growth hormone receptor at all.
The animal work supports that mechanistic claim reasonably well. In the key Endocrinology study, AOD9604 did not compete for the hGH receptor and did not induce cell proliferation in the assays that were run, yet it still increased in vivo fat oxidation and raised plasma glycerol, a standard index of lipolysis (PubMed 11713213). The same paper used beta-3 adrenergic receptor knockout mice, pointing to beta-3 adrenergic signaling in adipose tissue as part of the pathway. Crucially, full-length hGH in that experiment produced hyperglycemia and reduced insulin secretion. AOD9604 did not.
So the "growth hormone benefits without growth hormone problems" framing is not marketing invention. It is a real finding — in mice. The question that decides everything is whether that mechanism produces enough fat loss in a human body to matter, and that is where the story turns.
What the animal studies actually found
The preclinical package is the strongest part of the AOD9604 file, and it deserves credit.
Obese Zucker rats, oral dosing, 19 days
Ng and colleagues gave AOD9604 orally to genetically obese Zucker rats and reported more than a 50% reduction in body weight gain versus controls, with increased lipolytic activity in adipose tissue and no deterioration in insulin sensitivity on euglycemic clamp. The authors concluded the fragment "may have the potential to be developed into an orally usable and safe therapeutic agent for obesity" (PubMed 11146367).
Obese mice, 14 days, head-to-head with hGH
Both hGH and AOD9604 reduced weight gain and increased fat oxidation, but only hGH caused the glucose and insulin disturbances. The authors argued that fragments of hGH "can act in a manner novel to traditional hGH-stimulated pathways", supporting the idea of growth hormone as a pro-hormone with independently active pieces (PubMed 11673763).
Rabbit osteoarthritis model, intra-articular injection
A separate 2015 study injected AOD9604 into rabbit knee joints, with and without hyaluronic acid, in an osteoarthritis model (PubMed 26275694). This single rabbit study is the entire basis for the "AOD9604 repairs cartilage" claims you will see on sales pages. There is no human joint trial.
Consistent effects across two rodent species, a plausible mechanism, and a clean metabolic profile is exactly the profile that gets a compound into human trials. It did.
Does AOD9604 work for weight loss in humans?
On the available evidence, no — not to any degree that would clear a regulatory bar.
Metabolic Pharmaceuticals ran a sequence of human studies through the 2000s, reportedly six in total, using an oral formulation. Early Phase 2 work in a few dozen participants reported statistically significant weight loss and improved glucose tolerance over 12 weeks against placebo. The company then ran a larger Phase 2b trial in roughly 300 people with obesity. Sponsor announcements from 2004 described the best-performing arm losing on the order of 2.8 kg over 12 weeks compared with about 0.8 kg on placebo.
Read that number carefully, because it is the number that gets quoted everywhere as proof AOD9604 works. A placebo-adjusted difference of roughly 2 kg is about 2% of body weight for a typical trial participant. Regulators generally look for a placebo-adjusted weight reduction of at least 5% before considering an obesity drug clinically meaningful, and modern agents clear that by a wide margin (PubMed 23092275). The headline result from the best AOD9604 arm was, on its own terms, a weak signal.
Then it got worse. The confirmatory study — the one that added a structured diet and exercise program on top — failed to show a statistically significant separation from placebo. Metabolic Pharmaceuticals halted the obesity drug development program in 2007. No Phase 3 was ever run. No New Drug Application was ever filed anywhere in the world.
There is a second, quieter problem. The failed pivotal trial was never published as a peer-reviewed paper indexed on PubMed. That is common for negative industry results and it is precisely why the internet's picture of AOD9604 is frozen in 2004. A 2026 Sports Medicine review of approved and unapproved peptide therapies places AOD9604 in the "gray market" category and makes the general point plainly: these compounds show favorable metabolic outcomes in animal models, but "rigorous human safety data are scarce" and the potential for harm is real (PubMed 41966639).
One more detail almost nobody mentions. The human trials used oral AOD9604. The product sold today is almost universally an injectable powder for reconstitution. Even if you accepted the modest oral trial results at face value, they do not automatically transfer to a different route of administration with different pharmacokinetics.
AOD9604 vs approved weight-loss drugs
The most useful way to judge AOD9604 is next to compounds that were tested the same way and did clear the bar. Every figure below is the headline result from a published randomized trial.
| Compound | Class | Status | Best published weight result | Source |
|---|---|---|---|---|
| AOD9604 | hGH C-terminal fragment | Not approved; development halted 2007 | ~2 kg placebo-adjusted at 12 weeks in one Phase 2b arm; not reproduced in the confirmatory trial | Sponsor reports; no PubMed-indexed efficacy paper |
| Liraglutide 3.0 mg | GLP-1 receptor agonist | FDA approved for weight management | −8.0% body weight at 56 weeks (SCALE) | PubMed 26132939 |
| Semaglutide 2.4 mg | GLP-1 receptor agonist | FDA approved for weight management | −14.9% body weight at 68 weeks (STEP 1) | PubMed 33567185 |
| Tirzepatide 15 mg | GIP + GLP-1 dual agonist | FDA approved for weight management | −20.9% body weight at 72 weeks (SURMOUNT-1) | PubMed 35658024 |
| Retatrutide 12 mg | GIP + GLP-1 + glucagon triple agonist | Investigational; Phase 3 ongoing | −24.2% body weight at 48 weeks (Phase 2) | PubMed 37366315 |
This is not a close comparison. The gap between AOD9604 and the current GLP-1 receptor agonist class is the difference between a signal that vanished on replication and effects large enough to change cardiometabolic outcomes. If your interest is body weight, the honest read is that AOD9604 is not in the conversation. Our overview of peptides studied for weight loss covers where each compound actually sits.
AOD9604 side effects reported in trials
Here is where AOD9604 genuinely looks good, and it is worth saying clearly because honest reporting cuts both ways.
Across the company's human studies, AOD9604 was reported as safe and well tolerated, with no consistent excess of adverse events over placebo. Specifically, it did not reproduce the growth-hormone problems it was designed to avoid: no meaningful IGF-1 elevation, no hyperglycemia, no reported effect on insulin sensitivity. That is unusual for a compound in this space. Most gray-market peptides have no controlled human safety data at all.
But three caveats matter more than the headline.
- Short exposure, oral route. The safety record covers roughly 12-week oral dosing. It says nothing about years of subcutaneous injection, which is how people use it now.
- Absence of evidence is not evidence of safety. A few hundred participants over three months cannot detect uncommon or delayed harms. Nothing about AOD9604 has been studied at the scale that would.
- The vial is the real risk. A published forensic analysis of pharmaceutical preparations seized by Belgian authorities specifically examined AOD9604 products and found the practical problem with unregulated peptides: what is on the label and what is in the vial are separate questions (PubMed 24976118). Contamination, wrong peptide, wrong quantity, and non-sterile preparation are the documented hazards.
Anecdotally reported effects from injectable use — injection-site redness or irritation, headache, mild nausea, transient fatigue — are not from controlled trials and should be treated as user reports, not findings.
Is AOD9604 FDA approved?
No, and the confusion around this question is deliberate on the part of some sellers.
AOD9604 has never completed a Phase 3 trial, no sponsor has submitted a New Drug Application for it, and the FDA has never issued an approval letter for any AOD9604 product for any indication. It is not an approved obesity drug in the United States, the European Union, the United Kingdom, or Australia, where it was developed.
What did happen is separate and much narrower. In 2014, after the drug program had already been abandoned, the sponsor pursued a self-affirmed GRAS determination — Generally Recognized As Safe — for AOD9604 as an ingredient in foods, beverages, and dietary supplements at intakes up to about 1 mg per day. Two things about that:
- Self-affirmed GRAS is a conclusion reached by an expert panel commissioned by the company, under a food-law framework. It is not an FDA drug approval and it is not an FDA efficacy finding.
- GRAS addresses safety at food-level intakes. It says nothing whatsoever about whether the ingredient causes weight loss. The compound reached that classification precisely because it was so bland — the same clean tolerability profile that made it a failed drug made it an easy food ingredient.
When a sales page says "FDA GRAS approved for fat loss", every clause of that sentence is doing something misleading. This is one of the clearest examples in the peptide market of a regulatory status being laundered into an efficacy claim, and it is worth recognizing the pattern because it recurs — see our guide to how peptide legality actually works.
Is AOD9604 legal? Supplements, compounding, and sport
AOD9604 is not a controlled substance in the United States. That does not make it freely legal to sell for human use, and its regulatory position tightened considerably in recent years.
Compounding pharmacies
The route by which many US clinics supplied AOD9604 was compounding under section 503A of the Federal Food, Drug, and Cosmetic Act. That requires the substance to appear on FDA's 503A bulk drug substances list. On 4 December 2024, the FDA's Pharmacy Compounding Advisory Committee reviewed AOD9604 free base and AOD9604 acetate and voted 0 to 12 against inclusion. There is now no 503A compounding pathway for AOD9604 in the United States.
Supplements and cosmetics
In parallel, AOD9604 has been marketed in some jurisdictions through the food and supplement channel on the back of its GRAS determination, and pushed into topical and cosmetic positioning. These are different regulatory categories with much lower evidence requirements than drug approval, and a product being legally sellable as an ingredient tells you nothing about whether an injected version does anything.
Sport
The World Anti-Doping Agency names growth hormone fragments explicitly in section S2 of the Prohibited List — "growth hormone fragments, e.g. AOD-9604 and hGH 176-191" — which places them among substances prohibited at all times, in and out of competition. This is not theoretical: validated methods for detecting AOD9604 and its metabolites in doping-control samples have been published in Drug Testing and Analysis (PubMed 25208511). Any tested athlete using it is risking a sanction for a compound with no demonstrated performance or body-composition benefit.
Why AOD9604 is still everywhere online
A compound whose pivotal trial failed nineteen years ago should be a footnote. Instead AOD9604 is one of the most-searched fat-loss peptides on the internet. Five things explain that.
1. The story is unusually clean. "The fat-burning part of growth hormone, without the growth hormone side effects" is a single sentence that a non-scientist can understand and repeat. Most peptide pitches are not that tidy.
2. The safety record is real. Unlike most gray-market peptides, AOD9604 actually went through controlled human trials and came out with an unremarkable adverse-event profile. Marketers can point at that honestly, and then let readers assume safety implies efficacy.
3. GRAS gets mistranslated. As above, a food-ingredient safety classification reads to most people as "the FDA approved it".
4. Publication bias froze the record. The positive rodent papers from 2000 and 2001 and the optimistic 2004 press coverage are indexed, linkable, and citable. The negative confirmatory result exists mainly in corporate announcements and regulatory documents. Search engines and language models both weight what is published, so the internet's summary of AOD9604 is systematically more positive than the underlying evidence.
5. It is the anti-GLP-1 pitch. AOD9604 does not suppress appetite and does not slow gastric emptying, so it is marketed to people who want fat loss without the nausea associated with semaglutide and tirzepatide. That is a genuine appeal. It just happens to be attached to a compound that also does not reliably produce fat loss.
Understanding that pattern is more useful than any single fact about this peptide, because the same five mechanisms are what keep half a dozen other discontinued compounds circulating.
If you are already using it, track it properly
People make their own decisions, often after a conversation with a clinician we are not party to. If AOD9604 is part of what you are doing, the most valuable thing you can do is keep an honest record — because with a compound whose expected effect size is somewhere between small and zero, the only way to know whether anything is happening is data you did not collect selectively.
That means logging what you took and when, alongside body weight, waist measurement, training, and food intake, and being willing to look at a flat line and call it flat. It also means recording anything unexpected with dates attached, so you have something concrete to bring to a doctor rather than a vague recollection. If you are running it alongside anything else, see our notes on structuring a peptide log and the peptide Q&A library.
Frequently asked questions
Does AOD9604 actually burn fat?
In rodents, yes. Multiple published studies show AOD9604 increased fat oxidation, raised plasma glycerol, and reduced weight gain in obese mice and Zucker rats. In humans, the picture is different. Across the clinical program, weight loss was small in early trials and was not reproduced in the larger pivotal study that added diet and exercise. There is no human trial showing clinically meaningful fat loss from AOD9604.
Is AOD9604 FDA approved?
No. AOD9604 has never completed a Phase 3 trial, no company has filed a New Drug Application for it, and the FDA has never issued an approval letter for any AOD9604 product. The sponsor did obtain a self-affirmed GRAS determination in 2014 for use as a food and supplement ingredient, but GRAS is a safety classification for food use. It is not a drug approval and says nothing about weight-loss efficacy.
Is AOD9604 the same thing as HGH fragment 176-191?
They are closely related but not identical. hGH fragment 176-191 is the bare C-terminal sequence of human growth hormone. AOD9604 is that region, residues 177-191, with an extra tyrosine added at the N-terminus, giving a 16-amino-acid peptide. Sellers use the two names interchangeably, so a product labeled one way may contain the other, or a mixture.
What are the side effects of AOD9604?
In the company-run clinical trials AOD9604 was reported as well tolerated, with no consistent excess of adverse events over placebo and none of the glucose or IGF-1 effects seen with full growth hormone. That safety record covers short oral trials of about 12 weeks. Long-term safety has never been established, and users of injectable gray-market product commonly report injection-site redness, headache, and nausea.
How long does AOD9604 take to work?
The human studies were 12 weeks long, and that is the window in which any effect would have appeared. In the trials that reported a difference, the separation from placebo was small and emerged gradually over those three months. The larger confirmatory study running the same length found no significant benefit, so there is no evidence-based timeline to give for a meaningful result.
AOD9604 vs semaglutide: which has better evidence?
Semaglutide, by an enormous margin. In the STEP 1 trial, weekly semaglutide 2.4 mg produced roughly 15 percent mean body-weight loss at 68 weeks in nearly 2,000 participants, and it is an approved obesity medicine. AOD9604 never demonstrated clinically meaningful weight loss in any completed human trial and is not approved for obesity in any country.
Is AOD9604 legal to buy?
AOD9604 is not a controlled substance, but it is not an approved drug either. In December 2024 the FDA Pharmacy Compounding Advisory Committee voted unanimously against adding AOD9604 to the 503A bulk drug substances list, which removed the route for compounding pharmacies to prepare it for patients in the United States. Vials sold online are typically labeled research-use-only and are not intended for human use.
Can athletes use AOD9604?
No. The World Anti-Doping Agency lists growth hormone fragments including AOD9604 and hGH 176-191 in section S2 of the Prohibited List, which means they are banned at all times, in and out of competition. Validated detection methods for AOD9604 in urine and blood have been published, so an anti-doping laboratory can test for it directly.
Does AOD9604 raise IGF-1 or blood sugar like growth hormone?
The published work says no. AOD9604 does not compete for the growth hormone receptor and did not produce the hyperglycemia or reduced insulin secretion that full-length human growth hormone caused in the same animal experiments. That separation from classic growth hormone effects is the whole design premise of the molecule, and it is the part of the science that has held up best.
Why is AOD9604 still so popular online if the trials failed?
Three reasons. The mechanism story is simple and appealing, the safety record genuinely is clean compared with most gray-market peptides, and the failed pivotal trial was never published in a peer-reviewed journal. Search results are therefore dominated by positive rodent papers from 2000 to 2004 and by press releases from the early phase trials, while the negative outcome lives mostly in regulatory filings.
Sources
Every claim above traces to peer-reviewed literature indexed on PubMed, or to named regulatory records:
- The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and beta(3)-AR knock-out mice — PubMed 11713213
- Increase of fat oxidation and weight loss in obese mice caused by chronic treatment with human growth hormone or a modified C-terminal fragment — PubMed 11673763
- Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone — PubMed 11146367
- AOD-9604 Metabolic — PubMed 15134286
- Effect of Intra-articular Injection of AOD9604 with or without Hyaluronic Acid in Rabbit Osteoarthritis Model — PubMed 26275694
- Detection and in vitro metabolism of AOD9604 — PubMed 25208511
- Identification and characterization of peptide drugs in unknown pharmaceutical preparations seized by the Belgian authorities: case report on AOD9604 — PubMed 24976118
- Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance — PubMed 41966639
- Obesity pharmacotherapy: current perspectives and future directions — PubMed 23092275
- Once-Weekly Semaglutide in Adults with Overweight or Obesity — PubMed 33567185
- Tirzepatide Once Weekly for the Treatment of Obesity — PubMed 35658024
- A Randomized, Controlled Trial of 3.0 mg of Liraglutide in Weight Management — PubMed 26132939
- Triple-Hormone-Receptor Agonist Retatrutide for Obesity — PubMed 37366315
- The role of growth hormone secretagogues in the modern clinic — PubMed 32257855
- Biochemistry, Peptide — PubMed 32965931
Regulatory records referenced: FDA Pharmacy Compounding Advisory Committee meeting of 4 December 2024 (AOD-9604 free base and AOD-9604 acetate, 503A bulk drug substances review), and the WADA Prohibited List, section S2, Peptide Hormones, Growth Factors, Related Substances and Mimetics.