thymosin α-1 vs tb-500

updated October 25, 2026

thymosin α-1 (tier B) vs tb-500 (tier A): what each is, why each got its grade, half-life and source counts side by side.

thymosin α-1 · tier B

thymic immune peptide. approved abroad for hepatitis B. used stateside for generic 'immune support.'

tier rationale

B-tier reflects an unusual strength: thymosin alpha-1 has more real human evidence than almost anything near this grade. Multiple RCTs, several meta-analyses, approval as a genuine drug in more than 35 countries, and a clean decades-long safety record. The on-label hepatitis B adjunct data are real, and the one Cochrane-proven benefit, fewer serious infections during chemotherapy and radiation, is real. That drug-grade human evidence earns the B. What keeps it off A is two-fold: where it was tested rigorously and broadly the big modern trials came back null (the TESTS sepsis trial, three failed hepatitis C Phase 3 trials, the melanoma trial that missed survival, mixed acute-COVID data), and the grey market buys it for indications with essentially no human evidence (long COVID, ME-CFS, general 'immune support'). It is not a C: the evidence here is real, deep, and drug-grade, not thin. It is a strong drug whose proven wins are narrow and whose community use runs ahead of the evidence.

tb-500 · tier A

names a 7-amino-acid fragment of thymosin beta-4, but the vial you buy is a coin toss: fragment, full-length protein, or mislabeled. the COA mass is the only thing that knows.

tier rationale

not actually thymosin β-4. it's a 7-amino-acid fragment of it, the actin-binding LKKTETQ sequence at positions 17-23. sold in the 2000s through the Australian equine veterinary market before crossing into human gray-market use. now widely discussed as BPC-157's companion in the "wolverine stack." the name refers to the actin-binding LKKTETQ fragment, but vendor vials frequently contain the full 43-amino-acid protein instead, and only the COA mass resolves which. either way the grade is the same. the preclinical base across skin, cornea, heart, and brain is large and reproducible, which keeps it above the lower tiers. but the human program has missed its pivotal phase 3 trials (SEER-1, ARISE-3, and SEER-3 in june 2026) and nothing is approved anywhere, which keeps it below S. A-tier: real biology, unfinished proof.

at a glance

reptides grades the research record and cites the literature behind every call. research reference only; not medical advice.