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Comparison

Thymosin Alpha-1 vs VIP

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

Thymosin Alpha-1 VIP
Class Thymic & immune Other
Evidence Clinical trials Clinical trials
Human trials ~40 ~12
Half-life ~2 hours ~1-2 minutes
Reported range 1.6-3.2 mg 50-150 mcg
Frequency 2x weekly Up to 4x daily intranasal in research protocols
Routes Subcutaneous Intranasal, Subcutaneous
FDA approved No No
Research use only Yes Yes
Banned in sport No No
Studied for Chronic hepatitis B and C, Immune modulation, Vaccine adjuvant research, Sepsis research Respiratory failure research, Chronic inflammatory response syndrome, Sarcoidosis research
Reported side effects Injection-site erythema, Transient fatigue, Mild flu-like symptoms Flushing, Hypotension, Diarrhoea, Nasal irritation

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.

VIP

Vasoactive intestinal peptide is a member of the secretin-glucagon family, acting at VPAC1 and VPAC2 receptors distributed across gut, lung, and nervous and immune tissue. It produces smooth muscle relaxation, vasodilation, bronchodilation and a broadly anti-inflammatory shift in cytokine profile, and in the lung it protects alveolar type II cells. The synthetic form aviptadil was trialled in COVID-related respiratory failure with contested results, and it has not been approved for that use.

Thymosin Alpha-1 vs VIP: common questions

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

Thymosin Alpha-1 is thymic & immune and VIP is other, so they act on different pathways. Thymosin Alpha-1: A thymic immunomodulatory peptide approved in more than 30 countries for hepatitis B and C, though not in the United States. VIP: A 28-residue neuropeptide with broad vasodilatory and immunomodulatory activity, trialled as aviptadil in acute respiratory failure.

Which has stronger evidence, Thymosin Alpha-1 or VIP?

They sit at the same evidence level: clinical trials. Thymosin Alpha-1 has about 40 human studies and VIP about 12.

Are Thymosin Alpha-1 and VIP FDA approved?

Neither is FDA approved for any indication.

References

Regulatory and primary sources

  1. PubChem compound record (CID 16130571) ↗ · structure, identifiers, synonyms
  2. FDA: Unapproved drugs and "research use only" products ↗ · regulatory status of non-approved products
  3. CAS Registry Number 62304-98-7 ↗ · chemical identity
  4. PubChem compound record (CID 16132300) ↗ · structure, identifiers, synonyms
  5. CAS Registry Number 37221-79-7 ↗ · chemical identity

Published literature

  1. Hannappel E. beta-Thymosins.Ann N Y Acad Sci 2007.PubMed 17468232 · doi:10.1196/annals.1415.018
  2. Ancell CD, Phipps J, Young L. Thymosin alpha-1.Am J Health Syst Pharm 2001.PubMed 11381492 · doi:10.1093/ajhp/58.10.886
  3. Hadden JW. T-cell adjuvants.Int J Immunopharmacol 1994.PubMed 7806429 · doi:10.1016/0192-0561(94)90090-6
  4. Hadden JW. Thymic endocrinology.Ann N Y Acad Sci 1998.PubMed 9629262 · doi:10.1111/j.1749-6632.1998.tb09574.x
  5. Rubin BK. Unmet needs in cystic fibrosis.Expert Opin Biol Ther 2018.PubMed 30063865 · doi:10.1080/14712598.2018.1484101
  6. Hoch K, Volk DE. Structures of Thymosin Proteins.Vitam Horm 2016.PubMed 27450728 · doi:10.1016/bs.vh.2016.04.009
  7. 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
  8. Simonova MA, Ivanov I, Shoshina NS, et al.. Aging and Thymosin Alpha-1.Int J Mol Sci 2025.PubMed 41373628 · doi:10.3390/ijms262311470
  9. Fahrenkrug J. VIP and PACAP.Results Probl Cell Differ 2010.PubMed 19859678 · doi:10.1007/400_2009_24
  10. García-García F, Acosta-Peña E, Venebra-Muñoz A, et al.. Sleep-inducing factors.CNS Neurol Disord Drug Targets 2009.PubMed 19689305 · doi:10.2174/187152709788921672
  11. Tajti J, Szok D, Majláth Z, et al.. Migraine and neuropeptides.Neuropeptides 2015.PubMed 26094101 · doi:10.1016/j.npep.2015.03.006
  12. Tervo T, Tervo K, Eränkö L. Ocular neuropeptides.Med Biol 1982.PubMed 6178909
  13. McConalogue K, Furness JB. Gastrointestinal neurotransmitters.Baillieres Clin Endocrinol Metab 1994.PubMed 7907863 · doi:10.1016/s0950-351x(05)80226-5
  14. Krejs GJ. VIPoma syndrome.Am J Med 1987.PubMed 3035922 · doi:10.1016/0002-9343(87)90425-6
  15. Youssef JG, Lavin P, Schoenfeld DA, et al.. The Use of IV Vasoactive Intestinal Peptide (Aviptadil) in Patients With Critical COVID-19 Respiratory Failure: Results of a 60-Day Randomized Controlled Trial.Crit Care Med 2022.PubMed 36044317 · doi:10.1097/CCM.0000000000005660
  16. Barnes PJ. Neuropeptides and asthma.Am Rev Respir Dis 1991.PubMed 1706152 · doi:10.1164/ajrccm/143.3_Pt_2.S28

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.