TB-500 + Sermorelin Stack: Evidence, Mechanism Overlap, and Protocol

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Does any human study test this stack?

No. FDA searched PubMed, Embase, ClinicalTrials.gov and other databases for its July 2026 evaluation and found no article in which TB-500 was given to a human for any condition; none of the three papers the product's nominator cited involved TB-500 in people [1].

That evaluation also found no in-vivo animal study of TB-500 for wound healing, the use FDA examined [1]. Even the name is loose: 'TB-500' is a common name, not an official drug name, and FDA found several salts and derivatives, including different active moieties, sold under it [1].

What TB-500 actually is

TB-500 is a synthetic 7-amino-acid fragment of thymosin beta-4, residues 17 to 23, Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH, N-acetylated, with a molecular weight of about 889 g/mol [1]. Full-length thymosin beta-4 is a 43-amino-acid protein; TB-500 is not that protein and is not thymosin alpha-1 [1]. It appears to have first been synthesized in 2003, and a veterinary preparation marketed for horses and greyhounds appeared in 2011 [1].

The repair rationale is borrowed from the parent protein: the nomination describes the LKKTETQ stretch as the actin-binding site behind thymosin beta-4's wound-healing effects [1]. For the fragment itself, an in-vitro scratch-wound test found that TB-500 at 50 micrograms/mL did not induce wound closure in fibroblast cultures; a shorter metabolite did show activity in vitro [1].

TB-500 is not an approved drug anywhere FDA checked: no USP or National Formulary monograph, no FDA-approved product containing it, and no listing in the European or Japanese pharmacopeias [1]. FDA found no approved TB-500 product in the countries it checked, including Canada, Australia, the UK, Germany and France, or authorization from the European Medicines Agency [1].

What sermorelin actually is

Sermorelin is a 29-amino-acid analogue of human growth hormone-releasing hormone, the shortest synthetic peptide with GHRH's full biological activity; it is not growth hormone [3]. It acts on the pituitary GHRH receptor to prompt release of the body's own GH. In a study of 30 healthy men aged 19 to 43 given GHRH(1-29)-NH2 intravenously or intranasally, the peptide was eliminated quickly after an intravenous dose, yet GH stayed elevated for about three hours [7].

Geref held two approvals: NDA 019863 for a 0.05 mg diagnostic test of the pituitary's ability to secrete GH (approved December 28, 1990) and NDA 020443 for 0.5 mg and 1 mg vials to treat idiopathic GH deficiency in children with growth failure (approved September 26, 1997) [2]. The maker discontinued both in 2008 and asked FDA to withdraw the applications; FDA withdrew them effective June 18, 2009, and in March 2013 determined the drug had not been withdrawn for safety or effectiveness reasons [2]. Geref was never approved for adults, anti-aging, weight loss or athletic performance [2].

Sermorelin products available in the United States today are compounded and are not FDA-approved; FDA does not review compounded drugs for safety, effectiveness or quality before marketing [8].

What the sermorelin studies showed

In the 1-year multicenter pediatric study, 110 previously untreated children received 30 micrograms per kg subcutaneously at bedtime and 86 were evaluable; mean height velocity rose from 4.1 cm/yr at baseline to 8.0 cm/yr at 6 months and 7.2 cm/yr at 12 months, with 74% classed as good responders at 6 months [9]. No adverse changes appeared in general biochemistry or hormone tests, fasting glucose did not change, IGF-I was not excessively raised, and sermorelin was well tolerated overall [9].

In the older-men study, 10 healthy men (mean age 68) received 0.5 mg and 1 mg in random order, each twice daily for 14 days, with a 14-day break between doses, and were compared with 9 young men (mean age 26); at the higher dose, 24-hour GH and IGF-I rose to levels not significantly different from the young men [5]. That was a short physiology study, not a trial of any clinical outcome [5].

Is there a shared mechanism to stack?

The sermorelin side is documented in humans: it raises GH and IGF-I, as above [5]. The TB-500 side is not: FDA found no human pharmacokinetic or pharmacodynamic data for TB-500 by any route [1]. Nothing in the human record shows the fragment raising IGF-1 locally or systemically, and the actin-binding explanation is a rationale rather than a measured effect [1].

Human studies of thymosin beta-4 products do exist, but none tested TB-500: an intravenous recombinant thymosin beta-4 phase 1 study in 54 healthy volunteers given single doses, with mild to moderate adverse events and no dose-limiting toxicity [10]; dry-eye drops in 72 adults where neither primary endpoint differed from placebo [11]; a 9-patient severe dry-eye trial [12]; and a 96-patient STEMI trial where the overall infarct-area difference was not significant [13].

Is there a protocol?

There is no approved dose and no human dosing study of TB-500; the nomination FDA reviewed proposed a 3 mg/mL lyophilized powder for subcutaneous or intramuscular injection, and doses used in trials of full-length recombinant thymosin beta-4, a different product, do not carry over to the fragment [1]. Any milligram schedule circulating online is a seller's protocol, not a studied one.

Sermorelin has no current approved dose either, because no sermorelin product is approved [2]. The doses that were actually studied were 30 micrograms per kg once daily subcutaneously at bedtime in the pediatric program [9] and 0.5 mg or 1 mg subcutaneously twice daily for 14 days in the older-men study [5]. Neither is a recommended dose for an adult stack.

Safety and regulatory status

For TB-500, FDA's adverse-event database search through March 26, 2025 retrieved no TB-500 reports, its food and supplement complaint system (January 1, 2004 to March 10, 2025) retrieved two cases about a blended TB-500 and BPC-157 product with no safety assessment, and FDA found no published case reports [1]. Safety in humans is unknown [1]. FDA's stated concern for injectable TB-500 is immunogenicity, potentially amplified by peptide aggregation and impurities; no study of TB-500 immunogenicity or aggregation and no nonclinical toxicity studies were found [1].

FDA also described a 40-year-old woman who used a 'research purposes only' product containing BPC-157 and TB-500 (5 mg/5 mg) subcutaneously twice daily and developed widespread skin hyperpigmentation and gum darkening within a week, recurring when she retried it two weeks later; because the product contained two peptides, FDA said it could not determine which, if either, caused the reaction [4].

TB-500 sits in the 'nominated but withdrawn' table of FDA's page on bulk substances that may raise significant safety risks, which holds substances previously in category 2 whose nominators withdrew them; removal from category 2 was not a finding that it is safe [14]. It appears in none of the three categories on FDA's list for state-licensed pharmacies and physicians or on FDA's list for outsourcing facilities [15][16]. FDA staff proposed against adding TB-500 to the pharmacy bulks list; FDA's advisory committee reviewed it on July 23, 2026 and voted in favor of adding it, but committee recommendations are nonbinding and TB-500 is not on the list [1][17]. HHS's October 2026 draft enforcement-discretion policy names TB-500 among six peptides and says HHS does not intend to take enforcement action against certain pharmacies and physicians if its conditions are met; it is a draft that is neither an approval nor a listing [8][18].

Sermorelin is not on FDA's safety-risk page, and it appears on the list for outsourcing facilities in category 1 (under evaluation), marked as a component of FDA-approved drugs [14][16]. It does not appear in any category on the list for state-licensed pharmacies and physicians, and it is not one of the six peptides in HHS's draft policy [15][18]. The 1-year pediatric study reported no adverse biochemical or hormonal changes and no change in fasting glucose [9]. None of that describes the combination.

In sport, WADA's 2026 Prohibited List names sermorelin in S2.2.4 and 'Thymosin-beta4 and its derivatives e.g. TB-500' in S2.3; both are prohibited at all times, in and out of competition [6].