This page summarizes safety themes around TB-500 as an experimental peptide. It is not medical advice and is not a recommendation for use in any context.
The short answer
There is no published human safety dataset for TB-500 — the thymosin beta-4 fragment — given by injection. The reason is easy to state: the first study designed to measure its safety, tolerability, and pharmacokinetics is a phase 1/2 sequential dose-escalation trial that only began recruiting in February 2026 and is not scheduled to finish until 2028 (NCT07487363). Everything else available is either tolerability data from the parent protein in different formulations, or uncollected anecdote.
What clinical trials of the parent protein report
Full-length thymosin beta-4 (Tβ4) has been given to hundreds of trial participants — as a topical gel for wounds, as eye drops, and intravenously after myocardial infarction — and the recurring theme in those programs is tolerability rather than toxicity.
A phase 2 dry-eye study randomized 72 subjects 1:1 to 0.1% Tβ4 eye drops or placebo for 28 days; it missed both primary endpoints but reported no safety signal (Sosne & Ousler, Clin Ophthalmol 2015).
The phase 3 ARISE-3 dry-eye trial enrolled 700 subjects and completed in 2021; the sponsor's topline release notes the drug's safety alongside the failure to meet primary outcomes (RegeneRx, March 2021; NCT03937882).
Randomized, placebo-controlled dose-response phase 2 trials in pressure ulcers and venous stasis ulcers (n=72 each) completed rather than being halted for safety (NCT00382174, NCT00832091).
Two caveats keep this from transferring: those studies used a different molecule (43 amino acids, not seven) and mostly non-systemic routes. A reassuring eye-drop safety profile says little about weekly milligram injections of an acetylated heptapeptide.
Effects reported in informal use
What circulates in user reports — injection-site redness and soreness, headache, transient fatigue, occasional light-headedness — is plausible for any injected peptide and completely uncharacterized in frequency. No pharmacovigilance system collects these reports, no denominator exists, and self-reported effects cannot separate the peptide from the diluent, the injection technique, or whatever else was taken alongside it.
Risks that are theoretical but not resolved
The fragment's best-documented biological property is that it drives angiogenesis — the seven-amino-acid actin-binding motif is essential for that activity (Philp et al., FASEB J 2003). Promoting new blood-vessel growth is the mechanism behind the healing claims and, at the same time, the reason for caution in anyone with a tumor or proliferative retinal disease. No study shows TB-500 causes or accelerates cancer; no study has been designed to exclude it either. That is an open question, not a reassurance.
A second unknown is chronic exposure. The parent protein's trial programs ran weeks, not years. There is no long-term human data for either molecule.
The risk nobody can dose around
The most concrete documented hazard is not pharmacological. When the Racing Medication and Testing Consortium had the University of California–Davis Kenneth L. Maddy Laboratory analyze TB-500-labeled products, the lab reported that many contained no thymosin beta-4 or any peptide derived from it, and that most contained no proteins, peptides, or amino acids at all — with a single sample confirmed as N-acetylated LKKTETQ (RMTC Thymosin β4 Bulletin).
In practical terms that means a buyer's exposure is to an unverified solution: unknown identity, unknown purity, unknown sterility, and no manufacturer accountable for any of the three. Careful dose arithmetic cannot compensate for an unknown numerator.
Sanction risk is a real consequence
For anyone in tested sport, the reliable adverse outcome of TB-500 is not medical. The WADA Prohibited List names "Thymosin-β4 and its derivatives e.g. TB-500" in category S2.3, prohibited at all times. Volleyball player Emma Brooks received a four-year sanction running to December 2028 for using BPC-157 and TB-500 (Sport Integrity Canada), and triathlete Anthony McCauley accepted a four-year ban beginning September 2025 after an investigation found possession and use (USADA). Neither case required a positive test.
Sport & Anti-Doping Warning
TB-500 (a thymosin beta-4 fragment) is classified as a prohibited peptide hormone/growth factor and has appeared in elite-sport doping investigations, including endurance running cases where it was used alongside EPO and other banned agents.
- >Overview of peptide hormones and growth factors on the WADA Prohibited List (S2)
- >Reporting on TB-500 and other experimental peptides in performance contexts
Use of TB-500 by athletes governed by anti-doping rules is generally treated as a serious violation, particularly when combined with other anabolic or blood-boosting drugs.