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Comparison

LL-37 vs Thymosin Alpha-1

LL-37 is healing & repair; Thymosin Alpha-1 is thymic & immune. They are compared here because they are frequently considered against each other, not because they act alike.

On published evidence alone, Thymosin Alpha-1 is the better documented of the two (clinical trials). That is a statement about the state of the literature, not a recommendation.

LL-37 Thymosin Alpha-1
Class Healing & repair Thymic & immune
Evidence Preliminary human Clinical trials
Human trials ~3 ~40
Half-life ~1 hour ~2 hours
Reported range 100-500 mcg 1.6-3.2 mg
Frequency Once daily, short courses 2x weekly
Routes Subcutaneous, Topical Subcutaneous
FDA approved No No
Research use only Yes Yes
Banned in sport No No
Studied for Antimicrobial research, Biofilm research, Wound healing Chronic hepatitis B and C, Immune modulation, Vaccine adjuvant research, Sepsis research
Reported side effects Injection-site inflammation, Flu-like symptoms, Flushing Injection-site erythema, Transient fatigue, Mild flu-like symptoms

LL-37

LL-37 is the active 37-residue fragment cleaved from human cathelicidin hCAP18, produced by neutrophils and epithelial cells. It disrupts bacterial membranes directly and also modulates host immunity by recruiting immune cells, neutralising endotoxin and influencing wound repair. Its biology is genuinely double-edged: the same peptide is implicated in the pathology of rosacea and psoriasis, so more is not straightforwardly better.

Thymosin Alpha-1

Thymosin alpha-1 is a 28-residue peptide originally isolated from thymic tissue. It acts largely through Toll-like receptor signalling on dendritic cells, promoting maturation of T cells and enhancing Th1 responses, natural killer cell activity and antigen presentation. Unlike most compounds on this site it has a substantial approved clinical history outside the US, including as an adjuvant in hepatitis B and C and in sepsis research.

LL-37 vs Thymosin Alpha-1: common questions

What is the difference between LL-37 and Thymosin Alpha-1?

LL-37 is healing & repair and Thymosin Alpha-1 is thymic & immune, so they act on different pathways. LL-37: The only human cathelicidin antimicrobial peptide, with broad antibacterial activity and a complicated immunomodulatory profile. Thymosin Alpha-1: A thymic immunomodulatory peptide approved in more than 30 countries for hepatitis B and C, though not in the United States.

Which has stronger evidence, LL-37 or Thymosin Alpha-1?

Thymosin Alpha-1 has the stronger evidence base (clinical trials, about 40 human studies) compared with LL-37 (preliminary human).

Are LL-37 and Thymosin Alpha-1 FDA approved?

Neither is FDA approved for any indication.

References

Regulatory and primary sources

  1. PubChem compound record (CID 16198951) ↗ · structure, identifiers, synonyms
  2. FDA: Unapproved drugs and "research use only" products ↗ · regulatory status of non-approved products
  3. CAS Registry Number 154947-66-7 ↗ · chemical identity
  4. PubChem compound record (CID 16130571) ↗ · structure, identifiers, synonyms
  5. CAS Registry Number 62304-98-7 ↗ · chemical identity

Published literature

  1. Ahn CS, Huang WW. Rosacea Pathogenesis.Dermatol Clin 2018.PubMed 29499802 · doi:10.1016/j.det.2017.11.001
  2. Ismailova A, White JH. Vitamin D, infections and immunity.Rev Endocr Metab Disord 2022.PubMed 34322844 · doi:10.1007/s11154-021-09679-5
  3. Malhotra S, Hayes D Jr, Wozniak DJ. Cystic Fibrosis and Pseudomonas aeruginosa: the Host-Microbe Interface.Clin Microbiol Rev 2019.PubMed 31142499 · doi:10.1128/CMR.00138-18
  4. Wang H, Zhou C. Advances in the pathogenesis of rosacea.Front Immunol 2025.PubMed 41646975 · doi:10.3389/fimmu.2025.1705588
  5. Takahashi T, Yamasaki K. Psoriasis and Antimicrobial Peptides.Int J Mol Sci 2020.PubMed 32947991 · doi:10.3390/ijms21186791
  6. Traidl S, Roesner L, Zeitvogel J, et al.. Eczema herpeticum in atopic dermatitis.Allergy 2021.PubMed 33844308 · doi:10.1111/all.14853
  7. Scheenstra MR, van Harten RM, Veldhuizen EJA, et al.. Cathelicidins Modulate TLR-Activation and Inflammation.Front Immunol 2020.PubMed 32582207 · doi:10.3389/fimmu.2020.01137
  8. Kwiecien K, Zegar A, Jung J, et al.. Architecture of antimicrobial skin defense.Cytokine Growth Factor Rev 2019.PubMed 31473081 · doi:10.1016/j.cytogfr.2019.08.001
  9. Hannappel E. beta-Thymosins.Ann N Y Acad Sci 2007.PubMed 17468232 · doi:10.1196/annals.1415.018
  10. Ancell CD, Phipps J, Young L. Thymosin alpha-1.Am J Health Syst Pharm 2001.PubMed 11381492 · doi:10.1093/ajhp/58.10.886
  11. Hadden JW. T-cell adjuvants.Int J Immunopharmacol 1994.PubMed 7806429 · doi:10.1016/0192-0561(94)90090-6
  12. Hadden JW. Thymic endocrinology.Ann N Y Acad Sci 1998.PubMed 9629262 · doi:10.1111/j.1749-6632.1998.tb09574.x
  13. Rubin BK. Unmet needs in cystic fibrosis.Expert Opin Biol Ther 2018.PubMed 30063865 · doi:10.1080/14712598.2018.1484101
  14. Hoch K, Volk DE. Structures of Thymosin Proteins.Vitam Horm 2016.PubMed 27450728 · doi:10.1016/bs.vh.2016.04.009
  15. Gu B, Zhou Y, Nie Y, et al.. Efficacy of thymosin α1 for sepsis: a systematic review and meta-analysis of randomized controlled trials.Front Cell Infect Microbiol 2025.PubMed 40969554 · doi:10.3389/fcimb.2025.1673959
  16. Simonova MA, Ivanov I, Shoshina NS, et al.. Aging and Thymosin Alpha-1.Int J Mol Sci 2025.PubMed 41373628 · doi:10.3390/ijms262311470

Literature retrieved from PubMed on October 16, 2026, favouring human studies and reviews. Numbered markers in the text show which paper supports which statement; uncited entries are background reading.

Read this first This page compares published reference data. It is not medical advice and not a recommendation to use either compound. Several compounds documented on this site are not approved for human use.