TB-500 vs. Epitalon: Different Research Questions, Limited Clinical Answers

What each peptide actually is

TB-500 is a synthetic 7-amino-acid fragment of thymosin beta-4: residues 17 to 23, N-acetylated, Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH, molecular weight about 889 g/mol. It is not the full 43-amino-acid protein, and it is 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 [3].

Epitalon (also spelled epithalon) is a synthetic tetrapeptide, Ala-Glu-Asp-Gly, with a molecular weight of about 390 g/mol as the free base and about 450 g/mol as the acetate. It was designed from the amino-acid content of epithalamin, a polypeptide extract of animal pineal gland. FDA treats epitalon and epithalamin as different substances, so the older epithalamin studies are not studies of epitalon [1].

Both are sold as research-use-only vials: TB-500 as 2 mg to 15 mg injectable powder, alone or blended with BPC-157; epitalon as 10 mg to 50 mg vials, capsules and oral sprays [1][3].

What has been studied in place of TB-500

The human data usually cited for TB-500 belong to full-length thymosin beta-4, a different molecule. A 2021 phase 1 trial of recombinant human thymosin beta-4 (NL005) gave 54 healthy volunteers a single intravenous dose of 0.05 to 25 microgram/kg across seven cohorts, plus placebo, and gave 30 volunteers 0.5, 2 or 5 microgram/kg daily for 10 days. Adverse events were mild to moderate, with no dose-limiting toxicity or serious adverse events and no obvious accumulation [9]. The same applies to the RGN-259 eye-drop trials in dry eye, where 72 adults received 0.1% thymosin beta-4 drops or placebo for 28 days and neither primary endpoint differed significantly [10], and to a 2025 trial of recombinant thymosin beta-4 in 96 patients after a heart attack, where the overall difference was not significant [11].

On TB-500 itself the laboratory record is thin. In an in-vitro scratch-wound test, TB-500 at 50 microgram/mL did not induce wound closure in fibroblast cultures, while a shorter metabolite, N-acetylated LKKTE, did show activity [3]. No in-vivo animal study of TB-500 for wound healing was found, and no human pharmacokinetic or pharmacodynamic data exist for any route. Animal work with subcutaneous or intraperitoneal dosing shows the peptide reaches the bloodstream and is hydrolyzed into smaller peptides; no intramuscular animal studies were found [3].

Two reports do involve people, and neither establishes that TB-500 works. FDA described a safety report involving a product that contained both BPC-157 and TB-500: a 40-year-old woman used the 5 mg/5 mg research-only combination subcutaneously twice daily and developed widespread skin hyperpigmentation and gum darkening within a week, which recurred when she re-tried the product two weeks later; because the product held two peptides, FDA said it cannot tell whether either caused it [12]. A separate retrospective chart review at one Florida clinic reached 16 patients by phone after intra-articular peptide injections; 4 had BPC-157 plus thymosin beta-4 in an unspecified form, and 3 of those 4 reported significant improvement, with no control group and no validated measurement tool [13].

What did the epitalon studies measure?

FDA evaluated epitalon for insomnia and found no study of it in people with insomnia; the relevant human work measured a melatonin metabolite rather than sleep [1]. One placebo-controlled sublingual study enrolled 75 healthy women aged 40 to 50, mostly night-shift workers; 40 with low melatonin output were split into two groups of 20 and given a sublingual spray delivering about 0.5 mg/day or placebo for 20 days. Urinary 6-sulfatoxymelatonin rose about 1.7-fold on epitalon and did not change on placebo, and 83% versus 25% were described as improved in mood and physical condition. Sleep outcomes were not measured and blinding was not specified [1].

The other human setting is retinitis pigmentosa, where epitalon was injected beside the eye. The published report describes a 'positive clinical effect in 90% of the cases' in patients with degenerative retinal lesions, gives no sample size, design details or case numbers, and has not been replicated [14].

A 2026 narrative review searched through 22 September 2026 and concluded that human evidence is limited to small physiological or biomarker studies and an older controlled retinitis pigmentosa study; that no adequately powered randomized trial has established efficacy; that pharmacokinetic, dose-ranging and long-term safety data are inadequate; and that epitalon is 'biologically active but clinically unproven' [15].

The telomere findings come from cells. Adding epitalon to telomerase-negative human fetal fibroblast cultures induced the catalytic subunit of telomerase, telomerase activity and telomere elongation [2]. A 2025 study found dose-dependent telomere extension in normal epithelial and fibroblast cells through hTERT and telomerase upregulation, and in breast cancer cell lines through alternative lengthening of telomeres [16]. Neither experiment treated a person.

Is there any evidence for the TB-500 plus epitalon stack?

FDA searched PubMed, Embase, ClinicalTrials.gov and other sources and found no article in which TB-500 was given to a human [3]. That leaves no human evidence for a combination containing it. A 2026 narrative review of therapeutic peptides in gerontology, which covered both peptides, listed combination therapy effects among the significant knowledge gaps [17].

The proposed uses do not line up. The TB-500 nomination describes the LKKTETQ stretch as the actin-binding site behind thymosin beta-4's wound-healing effects [3]. Epitalon's reported activity is telomerase activation in cell culture [2] and a rise in a urinary melatonin metabolite in one small sublingual study [1]. Two separate sets of findings do not add up to a tested combination.

Regulatory status of both peptides

Neither is FDA-approved. FDA's July 2026 review found no USP or National Formulary monograph for either, no approved product in Canada, Australia, the UK, Belgium, Ireland, France, Norway, Germany, Spain or Italy, and nothing authorized by the European Medicines Agency [1][3]. Epitalon did hold an orphan drug designation for retinitis pigmentosa, granted 2 September 2010 and withdrawn 6 January 2016 [1].

Both appear in the 'nominated but withdrawn' table of FDA's page on bulk substances that may raise significant safety risks. That table holds substances previously in category 2 whose nominators withdrew them, and removal from category 2 was not a finding that they are safe. FDA's stated concerns are that for TB-500 it 'has not identified any human exposure data', and that for epitalon it 'has not identified safety-related information regarding epitalon for the proposed route of administration'; injectable peptides may pose immunogenicity risk from aggregation and impurities [18].

Neither appears in any of the three categories on FDA's list for state-licensed pharmacies and physicians (updated 14 May 2026) or on FDA's list for outsourcing facilities (updated 21 March 2025), so FDA's category 1 policy does not cover them [6][7][8].

FDA staff proposed in July 2026 that neither substance be added to the pharmacy bulk-substance list. For TB-500 the reasons included inconsistent naming, unclear historical use, no human data of any kind, and no evidence of effectiveness for wound healing [3]. For epitalon they included that it is not well characterized, has limited historical use, has no evidence of effectiveness for insomnia, and has no clinical safety data [1]. The Pharmacy Compounding Advisory Committee voted in favor of adding TB-500 on 23 July 2026 and epitalon on 24 July 2026, against staff's recommendation; those votes are non-binding advice, neither substance is on the list, and adding one takes formal rulemaking [19][20].

HHS's draft enforcement-discretion policy for compounding with certain peptides, filed 28 October 2026 as Federal Register document 2026-22192 with publication scheduled for 30 October 2026 and comments due two weeks after publication, names both among six peptides. It says HHS 'does not intend to take enforcement action' against a state-licensed pharmacy, federal facility or licensed physician compounding with them if conditions are met, such as a single active ingredient, a patient-specific prescription, an FDA-registered manufacturer with a certificate of analysis, and the label 'This is a compounded drug product. Not for resale.' It covers epitalon acetate in intermittent subcutaneous or intramuscular courses and TB-500 acetate by subcutaneous or intramuscular injection. The notice states that it does not establish rights for any person and is not binding on HHS or the public; it is not an FDA approval and does not put either peptide on any list [20][21].

What does WADA say about each?

TB-500 is named in WADA's section S2.3 as 'Thymosin-beta4 and its derivatives e.g. TB-500'. It is prohibited at all times, in and out of competition, and appears on the 2026 Prohibited List and on the tracked-changes version of the 2027 List dated 26 August 2026 [4][5].

Epitalon is not named on either list. Class S0 prohibits any pharmacological substance with no current approval by a governmental regulatory health authority for human therapeutic use, and gives BPC-157 only as an example, with the phrase 'including but not limited to'. No WADA statement on whether epitalon falls under S0 was found [4][5].

Safety data and dosing

For TB-500, FDA's search of its adverse-event database through 26 March 2025 retrieved no reports, and its food and supplement complaint system (1 January 2004 to 10 March 2025) retrieved two cases about a blended TB-500 and BPC-157 product with no safety assessment. 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 was found, and no nonclinical toxicity studies of TB-500 were found [3].

For epitalon, FDA's adverse-event database search through 8 December 2025 and its complaint-system search through 5 December 2025 retrieved no reports. FDA found no clinical study that assessed epitalon's safety: one small study gave no safety data, and a Russian-language report said only 'no side effects' without dose, route or number of people. FDA concluded there are no clinical data supporting its safety and raised an immunogenicity concern for subcutaneous injection [1]. FDA also warned that because epitalon activates telomerase and lengthens telomeres, and longer telomeres are generally linked to higher cancer risk, it has a mechanistic potential to be carcinogenic; the mouse studies of cancer and chromosome damage used one fixed dose, female mice only and short exposure [1].

There is no approved dose for either. Websites FDA reviewed suggest 5 mg to 10 mg of epitalon per day by subcutaneous injection or orally, in cycles, with one site suggesting every four months; that is marketing, not evidence. The human studies FDA found used a sublingual spray delivering about 0.5 mg/day for 20 days and a parabulbar injection [1]. For TB-500 there is no human dosing study; the nomination proposed a 3 mg/mL lyophilized powder for subcutaneous or intramuscular injection, and doses used in trials of recombinant full-length thymosin beta-4 do not apply to the fragment [3].