Thymosin Alpha-1 and LL-37 are both "immune" peptides, but they play very different roles. Thymosin Alpha-1 is a thymic peptide that modulates T-cell function and is approved in some countries (as Zadaxin) for conditions like hepatitis. LL-37 is the human cathelicidin antimicrobial peptide — part of innate immunity that directly attacks microbes, with a notable double-edged role in inflammation. Neither is FDA-approved in the US.
At a glance
| Thymosin Alpha-1 | LL-37 | |
|---|---|---|
| Type | Thymic immune-modulating peptide | Cathelicidin antimicrobial peptide |
| Main role | Modulates T-cell / adaptive immunity | Directly attacks microbes (innate immunity) |
| Approval | Approved abroad (Zadaxin); not in US | Not a drug; endogenous peptide |
| Studied for | Hepatitis, immune support | Innate defense; also inflammatory disease |
| Double-edged? | Generally immune-supportive | Yes — also linked to inflammatory conditions |
The bottom line
Bottom line: Same broad category, different jobs. Thymosin Alpha-1 fine-tunes the adaptive immune system and is an approved medicine in several countries; LL-37 is a natural first-line antimicrobial whose biology is double-edged — protective but also implicated in inflammatory disease. Neither is FDA-approved domestically, and LL-37 in particular is a research subject, not a supplement.
Frequently asked questions
What's the difference between thymosin alpha-1 and LL-37?
Thymosin alpha-1 is a thymic peptide that modulates T-cell (adaptive) immunity and is approved abroad as a medicine, while LL-37 is a natural antimicrobial peptide of the innate immune system that directly attacks microbes and is not a drug.
Is LL-37 something you can take?
No. LL-37 is a natural human antimicrobial peptide, not an approved drug. Its biology is double-edged — it also contributes to inflammatory and autoimmune conditions — so it's a research subject rather than a supplement.
Is thymosin alpha-1 FDA-approved?
It is approved in a number of countries (as Zadaxin) for conditions like hepatitis, but it is not FDA-approved in the United States. LL-37 is not an approved drug anywhere.
References
Combined peer-reviewed sources from both peptide guides. Inclusion is not endorsement.
- Naylor PH, Quadrini K, Garaci E, Rasi G, Hadden JW. Immunopharmacology of thymosin alpha-1 and cytokine synergy. Ann N Y Acad Sci. 2007. Peer-reviewed study
- Dominari A, Hathaway D III, Pandav K, et al. Thymosin alpha-1: A comprehensive review of the literature. World J Virol. 2020. Peer-reviewed study
- Costantini C, Bellet MM, Pariano M, et al. A Reappraisal of Thymosin Alpha1 in Cancer Therapy. Front Oncol. 2019. Peer-reviewed study
- Ancell CD, Phipps J, Young L. Thymosin alpha-1. Am J Health Syst Pharm. 2001. Peer-reviewed study
- Simonova MA, Ivanov I, Shoshina NS, et al. Aging and Thymosin Alpha-1. Int J Mol Sci. 2025. Peer-reviewed study
- Pei F, Guan X, Wu J. Thymosin alpha 1 treatment for patients with sepsis. Expert Opin Biol Ther. 2018. Peer-reviewed study
- Vandamme D, Landuyt B, Luyten W, Schoofs L. A comprehensive summary of LL-37, the factotum human cathelicidin peptide. Cell Immunol. 2012. Peer-reviewed study
- Ramos R, Silva JP, Rodrigues AC, et al. Wound healing activity of the human antimicrobial peptide LL37. Peptides. 2011. Peer-reviewed study
- Piktel E, Niemirowicz K, Wnorowska U, et al. The Role of Cathelicidin LL-37 in Cancer Development. Arch Immunol Ther Exp (Warsz). 2016. Peer-reviewed study
- Otte JM, Zdebik AE, Brand S, et al. Effects of the cathelicidin LL-37 on intestinal epithelial barrier integrity. Regul Pept. 2009. Peer-reviewed study
- Leite ML, Duque HM, Rodrigues GR, et al. The LL-37 domain: A clue to cathelicidin immunomodulatory response?. Peptides. 2023. Peer-reviewed study
- Chinipardaz Z, Zhong JM, Yang S. Regulation of LL-37 in Bone and Periodontium Regeneration. Life (Basel). 2022. Peer-reviewed study