The answer so far
No. Thymosin alpha-1 and thymosin beta-4 are different peptides. TB-500 is commonly used for a fragment related to thymosin beta-4, although product names are not always consistent. Evidence for one molecule, formulation or route cannot automatically be transferred to another.15
On this page
Why do their names sound alike?
The term “thymosin” has been used for different peptides associated with research on the thymus, an organ involved in immune development. A shared family name is a clue to that research history, not proof that the substances have the same structure or effects. Thymosin alpha-1, thymosin beta-4 and the shorter fragment called TB-500 need to be identified separately on a product or in a paper.15
- Thymosin alpha-1An immune-related peptide; the synthetic form is called thymalfasin.
- ZadaxinA named alpha-1 medicine with a specific Italian vaccine-adjunct indication.
- Thymosin beta-4A different, longer peptide studied in several contexts, including eye formulations.
- TB-500A name used for a beta-4-related fragment; product naming can vary.
What is thymosin alpha-1 studied for?
Thymosin alpha-1, also called thymalfasin in synthetic form, is studied in relation to immune responses. A named Italian medicine, Zadaxin, is indicated as an adjunct to influenza vaccination in immunocompromised people. Separate studies of chronic hepatitis B and sepsis had different designs and mixed results; they do not establish a general immune or anti-ageing benefit. See the thymosin alpha-1 overview for the actual findings.234
What about thymosin beta-4 and TB-500?
Thymosin beta-4 is a different, longer peptide studied for processes including cell movement and repair. TB-500 has been used for a fragment related to beta-4, but the term may be used inconsistently by sellers. Researchers have tested particular beta-4 eye formulations in people; those studies do not establish that a TB-500 fragment or injected product heals an injury. Read the beta-4 and TB-500 comparison and the eye-trial guide.51
Does “immune” versus “repair” prove what each does?
These are useful descriptions of why the substances are investigated, not exclusive biological labels or evidence that a product produces an outcome. A laboratory response, an eye-trial result, a viral marker and a person’s recovery from injury are different measures. A real comparison would need to specify the molecule, complete product, route, population, outcome and harms. Similar names cannot supply those missing results.135
How does this relate to BPC-157 or stacks?
TB-500 and BPC-157 are often discussed together for recovery, and some seller-defined blends contain several ingredients. That does not mean they contain thymosin alpha-1, or prove that a combination works better than any ingredient alone. Check the full ingredient list and distinguish a seller’s formula from a study of that exact combination. For the recovery evidence, see BPC-157 and TB-500; for product testing, see what a certificate of analysis can show.5
Sources, kept close.
Selected supporting sources; this is not a complete literature review.
- Immunoregulatory effects of thymosin alpha-1 and beta-4Immunopharmacology / PubMed · Human-cell laboratory study, 1987
- Zadaxin: Italian summary of product characteristicsAgenzia Italiana del Farmaco · Italian product information, February 2026
- Thymosin alpha-1 for chronic hepatitis B: placebo-controlled trialJournal of Viral Hepatitis / PubMed · Randomised double-blind trial, 1999
- TESTS: thymosin alpha-1 for sepsisBMJ / PubMed Central · Randomised placebo-controlled phase 3 trial, corrected 2025
- TB-500: Pharmacy Compounding Advisory Committee briefingU.S. Food and Drug Administration · Regulatory briefing, specific nominated peptide