Pinc PeptideThe girly peptide research blog

Immune · 5 compounds · updated 8 October 2026

Best peptides for immune support, ranked by the human evidence

5 compounds are sold for immune support and infections. We rank them by how strong the evidence in people is, not by popularity. None of them is an FDA-approved drug.

Thymosin alpha-1 is a prescription drug in Italy, sold as Zadaxin, and its maker’s annual report for 2014 said it was approved in over 30 countries, but FDA has approved no product containing it123. In 2024, FDA found that the evidence did not support it for any of the 12 uses it examined2. We found no trial testing LL-37, a copy of a peptide the immune system makes to kill bacteria, as a general immune booster, and a gel version missed its main goal in a 149-person leg-ulcer trial456. FDA found no study that gave KPV to people by any route7. Thymalin, a Russian prescription drug made from calf thymus glands, is a mix of small peptides rather than one molecule; its human trials are small and mostly run by its developers, and it is not approved in the US89101112. VIP (vasoactive intestinal peptide) is sold in the US as a pharmacy-made nasal spray for mold illness, but we found no placebo-controlled trial of that use; the studies behind it were small, open-label and from one research group1314. Given by drip as aviptadil, it did not improve recovery or survival in a 461-patient trial in COVID-19 lung failure15.

In July 2026, FDA’s advisers voted 8 to 6, with one abstention, to recommend letting pharmacies make KPV, against the advice of FDA staff; FDA had not acted on the vote by 8 October 202616171819. The same committee voted 17 to 4 against allowing thymosin alpha-1 in December 202420. US pharmacies may make VIP for now while FDA reviews it, and FDA twice declined to authorize it for emergency use in COVID-1916212223. Independent lab tests are scarce: Finnrick, a testing service, failed 13 of 17 KPV samples it tested from March to September 2026, and it listed no VIP tests as of 7 October 20262425. People choose which samples to send, so the results are not a random survey26. Finnrick listed no tests of LL-37, thymalin or thymosin alpha-1 when we checked on 5 and 7 October 2026272829.

  1. Thymosin alpha-1

    AMixed resultsApproved abroad as Zadaxin; not in the US

    Thymosin alpha-1 is a lab-made copy of a natural peptide first found in the thymus, sold abroad as Zadaxin130. Large trials in sepsis and severe pancreatitis found no benefit, and US pharmacies may not make it313233.

    Does it work for immune support and fighting infections? Large trials in sepsis (1,106 people), hepatitis C (552) and severe pancreatitis (508) found no benefit on their main goals313234. Smaller trials disagree, and vaccine studies measured only antibodies35363738. We found no long COVID trial39.

  2. Thymalin

    BMixed resultsApproved in Russia as an injection; not in US

    Thymalin is a Russian prescription drug made from calf thymus glands: a mix of small peptides, not one molecule89. Its human trials are small and mostly run by its developers, and it is not approved in the US101112.

    Does it work for immune support and slowing aging? In hospital COVID-19 patients, two small trials co-authored by one of its developers found faster drops in blood markers, and one found fewer deaths910. Anti-aging claims rest on one developer report with unclear methods11.

  3. VIP (vasoactive intestinal peptide)

    BUntestedApproved abroad as part of Invicorp; not in US

    VIP is a natural nerve peptide sold in the US as a pharmacy-made nasal spray for mold illness (CIRS)40. We found no test of that use against a placebo1341. As the drug aviptadil, it failed a large COVID-19 trial15.

    Does it work for mold illness (CIRS)? We found no test of VIP against a placebo for mold illness; the three published studies were small, open-label and from one research group1314. In COVID-19 lung failure, a 461-patient trial found no benefit15.

  4. LL-37

    BUntestedNot approved for any use

    LL-37 is a lab-made copy of a peptide the immune system makes to kill bacteria4. A gel version missed its main goal in a 149-person ulcer trial, and we found no trial of it as a general immune booster56.

    Does it work for fighting infections and boosting immunity? We found no trial of lab-made LL-37 to treat infection or boost general immunity6. In a small trial on foot ulcers, most of them uninfected, the cream did not lower bacteria counts significantly42.

  5. KPV

    DUntestedNot approved for any use

    KPV is a lab-made peptide of three amino acids, copied from the tail of a hormone that calms inflammation7. It is sold for gut and skin problems, but FDA found no study of it in people7.

    Does it work for gut and skin inflammation? FDA found no human data on KPV by any route, and we found no registered KPV trial743. It reduced gut inflammation in mouse colitis models4445.

How we ranked them

Compounds that trials show work for this goal come first, then those with mixed results, then those with no controlled human trial for this goal that has public results, and last those that trials found do not work. Within each group, the stronger the human evidence (tier A to E), the higher the place. Ties go to compounds FDA has approved as a medicine, then to those approved only in other countries, then to those whose US approval was withdrawn, then to peptides over non-peptide drugs, then to the winner of a trial that compared the two directly. Popularity, price and how a product is marketed play no part. A high place is not a recommendation to use anything.

How we grade evidence →

Doses used in studies

Questions people ask

What peptide boosts the immune system?

Thymosin alpha-1 is sold abroad mainly for hepatitis B and to boost flu shots, but FDA’s 2024 review found that the evidence did not support it for any of the 12 uses it examined23. In a small study of older men given a flu shot, a fourfold antibody rise was more common on thymosin alpha-1 than on placebo, 69% versus 52%, but FDA called the results questionable, and vaccine studies measured antibodies rather than infections238. We found no trial of lab-made LL-37 as a general immune booster, and FDA found no study that gave KPV to people67.

Do immune peptides fight infections?

Not clearly in trials: in 1,106 adults with sepsis, a life-threatening response to infection, 28-day deaths were 23.4% on thymosin alpha-1 and 24.1% on placebo31. Its hepatitis B and COVID-19 trials disagree, and a 2026 Cochrane review rated the hepatitis B evidence very low certainty3536374647. In a small trial on diabetic foot ulcers, most of them uninfected, an LL-37 cream did not lower bacteria counts significantly42.

Are immune peptides safe?

Thymosin alpha-1 was usually well tolerated in trials, with irritation where it was injected the most common complaint, but labels abroad warn about its use in pregnancy, children, autoimmune disease and transplant patients2. FDA warns that LL-37 may trigger unwanted immune reactions, and that lab and animal findings suggest harm to male reproduction and tumor growth in some tissues33. FDA found no human safety data and no animal toxicity studies for KPV7.

Sources

  1. 1Banca Dati Farmaci: ZADAXIN (timosina alfa 1) 1.6 mg/ml powder and solvent for solution for injection, AIC 028364026 Agenzia Italiana del Farmaco (AIFA), accessed 5 Oct 2026. medicinali.aifa.gov.it
  2. 2FDA Evaluation of Thymosin Alpha-1 (Ta1)-Related Bulk Drug Substances (Ta1 free base and Ta1 acetate), briefing document for the Pharmacy Compounding Advisory Committee meeting of December 4, 2024 U.S. Food and Drug Administration, 15 Nov 2024. fda.gov
  3. 3SciClone Pharmaceuticals 2014 Annual Report (Form 10-K for fiscal 2014) SciClone Pharmaceuticals, Inc., 12 Mar 2015. annualreports.com
  4. 4CAMP_HUMAN (P49913): Cathelicidin antimicrobial peptide, including antibacterial peptide LL-37 (residues 134-170) UniProt Consortium, 2 Sep 2026. uniprot.org
  5. 5Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: A multicentric prospective randomized placebo-controlled clinical trial Wound Repair and Regeneration, Nov 2021. pubmed.ncbi.nlm.nih.gov
  6. 6ClinicalTrials.gov intervention search for ‘LL-37’ (20 records; only two gave LL-37 to people) ClinicalTrials.gov, accessed 5 Oct 2026. clinicaltrials.gov
  7. 7FDA Evaluation of KPV-Related Bulk Drug Substances (KPV (Free Base) and KPV Acetate), Pharmacy Compounding Advisory Committee briefing document U.S. Food and Drug Administration, 12 May 2026. fda.gov
  8. 8Тималин (Thymalin), lyophilizate for intramuscular injection 10 mg: instructions for use Vidal Russia drug reference, 25 Mar 2025. vidal.ru
  9. 9Results and Prospects of Using Activator of Hematopoietic Stem Cell Differentiation in Complex Therapy for Patients with COVID-19 Stem Cell Reviews and Reports, Feb 2021. pubmed.ncbi.nlm.nih.gov
  10. 10Peptide Drug Thymalin Regulates Immune Status in Severe COVID-19 Older Patients Advances in Gerontology, 2021. link.springer.com
  11. 11Peptides of pineal gland and thymus prolong human life Neuroendocrinology Letters, 2003. pubmed.ncbi.nlm.nih.gov
  12. 12Drugs@FDA via openFDA: search for active ingredient thymalin (no matches) U.S. Food and Drug Administration (openFDA), accessed 7 Oct 2026. api.fda.gov · data query
  13. 13Chronic inflammatory response syndrome: a review of the evidence of clinical efficacy of treatment Annals of Medicine and Surgery, Dec 2024. pmc.ncbi.nlm.nih.gov
  14. 14Vasoactive intestinal polypeptide (VIP) corrects chronic inflammatory response syndrome (CIRS) acquired following exposure to water-damaged buildings Health (Scientific Research Publishing), Mar 2013. scirp.org
  15. 15Intravenous aviptadil and remdesivir for treatment of COVID-19-associated hypoxaemic respiratory failure in the USA (TESICO): a randomised, placebo-controlled trial The Lancet Respiratory Medicine, Sep 2023. pubmed.ncbi.nlm.nih.gov
  16. 16Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act (categories list) U.S. Food and Drug Administration, 14 May 2026. fda.gov
  17. 17July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee U.S. Food and Drug Administration, 6 Aug 2026. fda.gov
  18. 18PEPTIDE-L WAVE! PCAC Approves Four Bulk Drug Substances for the 503A List FDA Law Blog (Hyman, Phelps & McNamara), 24 Jul 2026. thefdalawblog.com
  19. 19Federal Register search: FDA documents mentioning “503A” published since 1 July 2026 Federal Register, accessed 8 Oct 2026. federalregister.gov
  20. 20Final Summary Minutes of the Pharmacy Compounding Advisory Committee Meeting, December 4, 2024 U.S. Food and Drug Administration, 21 Feb 2025. fda.gov
  21. 21Bulk Drug Substances Used in Compounding Under Section 503A of the FD&C Act U.S. Food and Drug Administration, 14 May 2026. fda.gov
  22. 22US Food and Drug Administration Declines Emergency Use Authorization for ZYESAMI® (aviptadil) for Patients with Critical COVID-19 with Respiratory Failure NRx Pharmaceuticals via PR Newswire, 4 Nov 2021. prnewswire.com
  23. 23FDA Declines Emergency Use Authorization for ZYESAMI® (aviptadil) for subgroup of Patients with Critical COVID-19 at immediate risk of death from respiratory failure despite treatment with approved therapy, including remdesivir NRx Pharmaceuticals via PR Newswire, 1 Jul 2022. prnewswire.com
  24. 24KPV: safety testing results and vendor ratings Finnrick, 10 Sep 2026. finnrick.com
  25. 25VIP Safety Testing Results & Vendor Ratings Finnrick, accessed 7 Oct 2026. finnrick.com
  26. 26We’d Rather Buy the Future Than Wait For It Finnrick, 10 Jun 2026. finnrick.com
  27. 27LL-37: safety testing results and vendor ratings (no published tests) Finnrick, accessed 5 Oct 2026. finnrick.com
  28. 28Thymalin Safety Testing Results & Vendor Ratings Finnrick, accessed 7 Oct 2026. finnrick.com
  29. 29Thymosin Alpha 1: safety testing results and vendor ratings Finnrick, accessed 5 Oct 2026. finnrick.com
  30. 30Thymosin alpha1: isolation and sequence analysis of an immunologically active thymic polypeptide Proceedings of the National Academy of Sciences, Feb 1977. pubmed.ncbi.nlm.nih.gov
  31. 31The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial BMJ, 15 Jan 2025. pubmed.ncbi.nlm.nih.gov
  32. 32Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial Intensive Care Medicine, Jul 2022. pubmed.ncbi.nlm.nih.gov
  33. 33Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks U.S. Food and Drug Administration, 22 Apr 2026. fda.gov
  34. 34Thymosin alpha-1 with peginterferon alfa-2a/ribavirin for chronic hepatitis C not responsive to IFN/ribavirin: an adjuvant role? Journal of Viral Hepatitis, Jan 2012. pubmed.ncbi.nlm.nih.gov
  35. 35Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial Hepatology, May 1998. pubmed.ncbi.nlm.nih.gov
  36. 36Thymosin alpha1 treatment of chronic hepatitis B: results of a phase III multicentre, randomized, double-blind and placebo-controlled study Journal of Viral Hepatitis, Sep 1999. pubmed.ncbi.nlm.nih.gov
  37. 37A Double-blind Multicenter Two-arm Randomized Placebo-controlled Phase-III Clinical Study to Evaluate the Effectiveness and Safety of Thymosin α1 as an Add-on Treatment to Existing Standard of Care Treatment in Moderate-to-severe COVID-19 Patients Indian Journal of Critical Care Medicine, Aug 2022. pubmed.ncbi.nlm.nih.gov
  38. 38Augmentation of influenza antibody response in elderly men by thymosin alpha one. A double-blind placebo-controlled clinical study Journal of the American Geriatrics Society, Jan 1989. pubmed.ncbi.nlm.nih.gov
  39. 39ClinicalTrials.gov search: intervention ‘thymosin alpha’, condition ‘long COVID’ (0 studies) ClinicalTrials.gov, accessed 5 Oct 2026. clinicaltrials.gov
  40. 40VIP (Vasoactive Intestinal Peptide) nasal spray, compounded medication page Strive Pharmacy (vendor), accessed 7 Oct 2026. strivepharmacy.com (seller page, deliberately not linked)
  41. 41ClinicalTrials.gov search: chronic inflammatory response syndrome, mold illness, water-damaged building or biotoxin (5 records, none testing VIP) ClinicalTrials.gov, accessed 7 Oct 2026. clinicaltrials.gov
  42. 42Efficacy of LL-37 cream in enhancing healing of diabetic foot ulcer: a randomized double-blind controlled trial Archives of Dermatological Research, Nov 2023. pubmed.ncbi.nlm.nih.gov
  43. 43ClinicalTrials.gov search for ‘KPV’ (no registered study) ClinicalTrials.gov, accessed 5 Oct 2026. clinicaltrials.gov
  44. 44PepT1-mediated tripeptide KPV uptake reduces intestinal inflammation Gastroenterology, Jan 2008. pubmed.ncbi.nlm.nih.gov
  45. 45Melanocortin-derived tripeptide KPV has anti-inflammatory potential in murine models of inflammatory bowel disease Inflammatory Bowel Diseases, Mar 2008. pubmed.ncbi.nlm.nih.gov
  46. 46A Pilot Trial of Thymalfasin (Thymosin-α-1) to Treat Hospitalized Patients With Hypoxemia and Lymphocytopenia Due to Coronavirus Disease 2019 Infection Journal of Infectious Diseases, 11 Jan 2023. pubmed.ncbi.nlm.nih.gov
  47. 47Thymosin-α1 for people with chronic hepatitis B Cochrane Database of Systematic Reviews, 9 Sep 2026. pubmed.ncbi.nlm.nih.gov

Not medical advice. Each compound page cites its sources for every claim above. All compounds in one table · Report an error.