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Comparison

Thymalin vs Thymosin Alpha-1

Both are thymic & immune, so the meaningful differences are in kinetics, evidence and regulatory status.

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.

Thymalin Thymosin Alpha-1
Class Thymic & immune Thymic & immune
Evidence Preliminary human Clinical trials
Human trials ~5 ~40
Half-life Not established ~2 hours
Reported range 10-20 mg 1.6-3.2 mg
Frequency Once daily for 5-10 days 2x weekly
Routes Intramuscular, Subcutaneous Subcutaneous
FDA approved No No
Research use only Yes Yes
Banned in sport No No
Studied for Immune restoration research, Geriatric immunity research Chronic hepatitis B and C, Immune modulation, Vaccine adjuvant research, Sepsis research
Reported side effects Injection-site reactions, Transient fatigue Injection-site erythema, Transient fatigue, Mild flu-like symptoms

Thymalin

Thymalin is a mixture of polypeptide fractions isolated from bovine thymus rather than a single defined molecule, which is an important distinction from thymosin alpha-1. It is reported to restore T-lymphocyte differentiation and normalise immune indices in immunodeficiency states. The frequently cited evidence is a long-running Russian geriatric cohort reporting reduced mortality; that work has not been replicated under contemporary trial standards.

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.

Thymalin vs Thymosin Alpha-1: common questions

What is the difference between Thymalin and Thymosin Alpha-1?

Both are thymic & immune. Thymalin: A polypeptide fraction extracted from calf thymus, used clinically in Russia and studied in long-term geriatric cohorts. 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, Thymalin or Thymosin Alpha-1?

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

Are Thymalin and Thymosin Alpha-1 FDA approved?

Neither is FDA approved for any indication.

References

Regulatory and primary sources

  1. PubChem compound record (CID 3085284) ↗ · structure, identifiers, synonyms
  2. FDA: Unapproved drugs and "research use only" products ↗ · regulatory status of non-approved products
  3. PubChem compound record (CID 16130571) ↗ · structure, identifiers, synonyms
  4. CAS Registry Number 62304-98-7 ↗ · chemical identity

Published literature

  1. Khavinson VKh. Peptides and Ageing.Neuro Endocrinol Lett 2002.PubMed 12374906
  2. Khavinson VKh, Morozov VG. [Geroprotective effect of thymalin and epithalamin].Adv Gerontol 2002.PubMed 12577695
  3. Litvinenko GI, Shurlygina AV, Dergacheva TI, et al.. Chrono- and Immunocorrection of Inflammatory Disorders of Internal Reproductive Organs in Women of Reproductive Age.Bull Exp Biol Med 2015.PubMed 26033592 · doi:10.1007/s10517-015-2890-0
  4. Khavinson VKh, Morozov VG. Peptides of pineal gland and thymus prolong human life.Neuro Endocrinol Lett 2003.PubMed 14523363
  5. Lin'kova NS, Poliakova VO, Kvetnoĭ IM, et al.. [Characteristics of the pineal gland and thymus relationship in aging].Adv Gerontol 2011.PubMed 21809618
  6. Lin'kova NS, Poliakova VO, Trofimov AV, et al.. [Influence of peptides from pineal gland on thymus function at aging].Adv Gerontol 2010.PubMed 21510076
  7. Musienko GV. [Thymalin in the combined treatment of parkinsonism patients].Lik Sprava 1999.PubMed 10424021
  8. Domina EA. Chornobyl catastrophe: cytogenetic effects of low dose ionizing radiation and their modification.Exp Oncol 2016.PubMed 28230819
  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.