TB-500 + AOD-9604 Stack: Evidence, Mechanism Overlap, and Protocol Considerations

Is there any study of TB-500 with AOD-9604?

Because FDA found no article in which TB-500 was given to a human [1], there is no human study of the pair. The closest human record involves a different combination: a 2021 retrospective chart review at one Florida clinic reached 16 patients by phone after intra-articular peptide injections, 12 of whom had BPC-157 alone and 4 of whom had BPC-157 plus thymosin beta-4, with the form of the peptide unspecified [5]. AOD-9604 was not part of that review, and it cannot show that TB-500 works, so it says nothing about this stack.

What TB-500 actually is

TB-500 is a synthetic, N-acetylated seven-amino-acid peptide (Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln), corresponding to residues 17 to 23 of the 43-amino-acid protein thymosin beta-4, with a molecular weight of about 889 g/mol [1]. It is not full-length thymosin beta-4 and not thymosin alpha-1. 'TB-500' is a common name rather than an official drug name, and FDA found several salts and derivatives, including different active moieties, sold under it [1]. It appears to have been first synthesized in 2003 from thymosin beta-4, with a veterinary preparation marketed from 2011 for horses and greyhounds, and it is sold online as a 'research use only' injectable powder in 2 mg to 15 mg vials [1].

What AOD-9604 actually is

AOD-9604 is human growth hormone amino acids 177 to 191 with an extra tyrosine added at the N-terminus, a 16-amino-acid peptide also called hGH fragment 176-191; it is not full-length growth hormone [3]. An Australian company, Metabolic Pharmaceuticals, developed it as an anti-obesity drug candidate, and phase IIa trials were underway by February 2002 [6]. It never reached approval, and the obesity program was later dropped [2].

Do the two mechanisms overlap?

The two peptides have different described mechanisms.

For TB-500, the nomination FDA reviewed describes the LKKTETQ stretch of thymosin beta-4 as the actin-binding site behind its wound-healing claims [1]. For TB-500 itself, FDA found no in-vivo animal study of wound healing. In an in-vitro scratch-wound test, TB-500 at 50 micrograms/mL did not induce wound closure in fibroblast cultures, while a shorter metabolite, N-acetylated LKKTE, did show activity [1].

For AOD-9604, obese mice given intraperitoneal AOD9604 for 14 days lost body weight and body fat and had higher beta-3 adrenergic receptor RNA; in mice lacking that receptor, the long-term weight and lipolysis effects were not seen [7]. The same authors concluded that the lipolytic action of AOD9604 is not mediated directly through the beta-3 receptor, although both growth hormone and AOD9604 raise receptor expression [7]. A 2026 review adds that preclinical work found no growth-hormone-receptor binding [2].

So one compound is proposed to act through an actin-binding sequence tied to tissue repair and the other on fat-cell lipolysis. No shared receptor or shared pathway is described for the pair.

What human evidence exists for each peptide

For TB-500, FDA's July 2026 review searched PubMed, Embase, ClinicalTrials.gov and other sources and found no article in which TB-500 was given to a human, and none of the three papers the nominator cited involved TB-500 in humans [1]. Trials of full-length thymosin beta-4 are a different molecule and do not fill that gap: an intravenous recombinant human thymosin beta-4 phase 1 study in 54 healthy volunteers reported mild to moderate adverse events and no dose-limiting toxicity [8]; 0.1% thymosin beta-4 eye drops in 72 adults with dry eye missed both primary endpoints [9]; and a 96-patient STEMI trial found a smaller infarct area only in the subgroup dosed within 8 hours, with no significant overall difference [10].

For AOD-9604, the main human study is a 24-week oral obesity trial, 534 enrolled and 502 randomized, that failed to show significant benefit on the primary weight-loss endpoint; that conclusion rests on sponsor-reported phase 2 results rather than a peer-reviewed trial, and there is no PMID for the trial itself [2]. The same review notes no robust human data for visceral-fat reduction or other metabolic benefit [2]. Animal work is more extensive: obese Zucker rats given oral AOD9604 at 500 micrograms/kg daily for 19 days gained 15.8 g versus 35.6 g in controls, with higher fat-tissue lipolytic activity and no adverse effect on insulin sensitivity on euglycemic clamp [11]. A rabbit study of intra-articular AOD9604, with or without hyaluronic acid, in 32 animals improved cartilage scores and shortened lameness [12]; that rabbit work is the only support for joint-repair claims, and no convincing human osteoarthritis trial exists [12][2].

What is known about safety

For TB-500, FDA's review states that it has not identified any human exposure data and found no nonclinical toxicity studies and no immunogenicity or aggregation studies; its stated concern for injectable TB-500 is immunogenicity, potentially amplified by peptide aggregation and impurities [1]. FDA found no published case reports; a search of FDA's adverse-event database through March 26, 2025 retrieved no TB-500 reports, and FDA's food and supplement complaint system from January 1, 2004 to March 10, 2025 retrieved two cases involving a blended TB-500 and BPC-157 product with no safety assessment [1].

One case is described in FDA's BPC-157 review: a 40-year-old woman who used a 'research purposes only' BPC-157 plus TB-500 (5 mg/5 mg) product subcutaneously twice daily developed widespread skin hyperpigmentation and gum darkening within a week, and the reaction recurred when she re-tried the product two weeks later; with two peptides in the product, FDA said it cannot tell whether either caused it [13].

For AOD-9604, FDA states that it 'has also identified serious adverse events that may be associated with AOD-9604, though causality is not clear,' and gives no details [4]. A 2026 review concludes that human evidence is limited and largely short-term [2].

Regulatory status of each peptide

Neither compound is approved for any human use [1][2]. Both appear in the 'nominated but withdrawn' table on FDA's page about bulk substances that may raise significant safety risks, a table that holds substances previously in category 2 whose nominators withdrew them; removal from category 2 was not a finding that either is safe [4]. Neither appears in any of the three categories on FDA's list for state-licensed pharmacies and physicians (updated May 14, 2026) or on FDA's list for outsourcing facilities (updated March 21, 2025), and the category 1 policy, under which FDA generally takes no action against compounders who meet its conditions, does not cover them [14][15][16].

For TB-500, FDA staff proposed in a July 2026 briefing document that neither the free base nor the acetate be added to the pharmacy bulks list, citing inconsistent naming, missing impurity, aggregate and endotoxin data, no human data of any kind, no evidence of effectiveness for wound healing, immunogenicity risk for injection, and the existence of FDA-approved wound treatments [1]. The Pharmacy Compounding Advisory Committee reviewed TB-500 on July 23, 2026 and voted in favor of adding it, against staff's recommendation; that advice is non-binding and TB-500 is not on the list, which takes formal rulemaking [17][1].

HHS's draft enforcement-discretion policy for compounding with certain peptides, filed October 28, 2026 as Federal Register document 2026-22192, names TB-500 among six peptides and covers the acetate form given by subcutaneous or intramuscular injection [18][19]. The notice says HHS does not intend to take enforcement action against a state-licensed pharmacy, federal facility or licensed physician compounding with it if the policy's conditions are met, that it does not establish any rights and is not binding on HHS or the public, and that HHS may revisit it [18]. It is not an approval and does not place TB-500 on any list [18]. AOD-9604 is not one of the six peptides in that draft policy [18]. Compounded drugs are not FDA-approved; FDA does not review their safety, effectiveness or quality before marketing [18].

Both peptides are also banned in sport. WADA's Prohibited List names AOD-9604 and hGH 176-191 in S2.2.3 as growth hormone fragments and 'Thymosin-beta4 and its derivatives e.g. TB-500' in S2.3; both are prohibited at all times, in and out of competition, and appear on the 2026 List and the 2027 List [20][21].

What about protocols and dosing?

No approved dose exists for either peptide [1][2]. TB-500 has no human dosing study at all; the nomination FDA reviewed proposed a 3 mg/mL lyophilized powder for subcutaneous or intramuscular injection, and FDA found no human pharmacokinetic or pharmacodynamic data for TB-500 by any route [1]. AOD-9604's human obesity testing used an oral drug candidate, and no efficacy trial of injected gray-market AOD-9604 has been identified [2]. Doses from trials of recombinant full-length thymosin beta-4, such as the 0.05 to 25 micrograms/kg intravenous single doses in the phase 1 study, do not apply to TB-500 [8][1].

Because no human study of TB-500 exists, no seller protocol for the pair has a human trial behind it.