TB-500 Sourcing and Purity Risks: What You're Actually Injecting

What a TB-500 vial actually contains

TB-500 is a synthetic 7-amino-acid, N-acetylated fragment of the 43-amino-acid protein thymosin beta-4, spanning residues 17 to 23, with a molecular weight of about 889 g/mol [1]. It is not full-length thymosin beta-4 and not thymosin alpha-1 [1].

'TB-500' is a common name, not an official drug name, and FDA found several salts and derivatives, including different active moieties, sold under that same name [1]. So the name on a vial is not a reliable statement of which molecule is inside it.

TB-500 appears to have first been synthesized in 2003 from thymosin beta-4, and a veterinary preparation appeared in 2011, marketed to boost performance in horses and greyhounds [1]. It is sold online as a 'research use only' injectable powder in vials from 2 mg to 15 mg, alone or blended with BPC-157. FDA found no pharmacy marketing a compounded TB-500 product and no outsourcing facility reporting one [1].

What FDA found about TB-500 quality standards

FDA's July 2026 review found no USP or National Formulary monograph for TB-500, no FDA-approved drug containing it, no entry in the European or Japanese pharmacopeias, and no approved product in Canada, Australia, the UK, Belgium, Ireland, France, Norway, Germany, Spain or Italy or authorized by the European Medicines Agency [1].

FDA staff's July 2026 briefing document proposed that neither TB-500 free base nor TB-500 acetate be added to the pharmacy bulks list. The reasons given: TB-500 is not well characterized, its naming is inconsistent, and there are no impurity, aggregate or endotoxin data; its historical use is unclear; there is no evidence of effectiveness for wound healing, the use FDA evaluated; there are no human data of any kind; injection carries an immunogenicity risk; and FDA-approved wound treatments already exist [1].

FDA's stated concerns about injecting TB-500

The concern FDA stated for injectable TB-500 is immunogenicity, an immune reaction to the peptide, potentially amplified by peptide aggregation and peptide-related impurities [1][5]. FDA found no study of TB-500 immunogenicity or aggregation, and no nonclinical toxicity studies [1].

FDA found no in-vivo animal studies of TB-500 for wound healing [1]. In a cell-culture scratch-wound test, TB-500 at 50 micrograms/mL did not induce wound closure in fibroblast cultures, while a shorter metabolite showed activity [1].

What FDA, its advisory committee and HHS have each done

TB-500 appears in the 'nominated but withdrawn' table on FDA's page for bulk substances that may present significant safety risks. That table holds substances previously in category 2 whose nominators withdrew them; removal from category 2 was not a finding that TB-500 is safe [5].

It appears in none of the three interim categories on FDA's list for state-licensed pharmacies, and it is not on FDA's list for outsourcing facilities [2][3][4].

FDA's Pharmacy Compounding Advisory Committee reviewed TB-500 on July 23, 2026 and voted in favor of adding it to the bulks list, against FDA staff's recommendation [8][9]. That is advice only and not binding. TB-500 is not on the list, and adding it takes formal rulemaking [9].

HHS filed a draft enforcement-discretion policy on October 28, 2026 (Federal Register document 2026-22192, publication scheduled October 30, 2026, comments due two weeks after publication) [9]. It names TB-500 among six peptides and covers TB-500 acetate given by subcutaneous or intramuscular injection. Under the draft, 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, such as a single active ingredient, a patient-specific prescription, an FDA-registered manufacturer with a certificate of analysis, and a label reading 'This is a compounded drug product. Not for resale.' [9][10]

The notice says the policy 'does not establish any rights for any person and is not binding on HHS or the public' [9]. It is not an FDA approval and does not put TB-500 on any list, and compounded drugs are not FDA-approved: FDA does not review their safety, effectiveness or quality before they are marketed [9].

Reported harms and what they do and do not show

FDA's adverse-event database returned no TB-500 reports through March 26, 2025, and FDA found no published case reports [1]. Its food and supplement complaint system, searched from January 1, 2004 to March 10, 2025, returned two cases concerning a 'blended TB-500 and BPC-157' product, with no safety assessment [1]. FDA's conclusion is that safety in humans is unknown [1].

FDA's review of BPC-157 describes one detailed case: a 40-year-old woman used a 'research purposes only' product containing BPC-157 plus TB-500 (5 mg/5 mg) subcutaneously twice daily and developed widespread skin hyperpigmentation and gum darkening within a week, which recurred when she tried the product again two weeks later [11]. Because the product contained two peptides, FDA said it cannot tell whether either one caused it [11].

What the thymosin beta-4 studies do and do not tell you

Full-length thymosin beta-4 is a different molecule from TB-500, and human studies of the full protein do not show that TB-500 works or is safe [1].

A phase 1 study in 54 healthy volunteers gave single intravenous doses of recombinant human thymosin beta-4 from 0.05 to 25 micrograms/kg, and another 30 volunteers received 0.5, 2 or 5 micrograms/kg daily for 10 days; adverse events were mild to moderate, with no dose-limiting toxicity or serious adverse events [12]. A randomized trial in 96 patients with STEMI after angioplasty found no significant overall difference in infarct area, although the subgroup given the first dose within 8 hours (n=43) had a smaller infarct area at 90 days [13]. Neither study used TB-500.

A 16-patient chart review at one Florida clinic followed people who had intra-articular peptide injections for knee pain: 12 received BPC-157 alone and 4 received BPC-157 plus thymosin beta-4 (form not specified). Three of those 4 reported significant improvement, but there was no control group, no validated measurement tool, and results were recalled by phone [14]. It cannot show that TB-500 works.

An analytical chemistry paper separately described the N-acetylated 17-23 fragment 'identified in TB-500, a product suspected to possess doping potential' [15]. That paper characterised the molecule; it tested nothing in people.