Compound family

Immune, antimicrobial and repair-signal peptides

In one sentenceA thymic immune modulator that failed its largest trial, the human antimicrobial peptide with two wound-healing trials, a gut hormone whose 461-person COVID trial found nothing, and an erythropoietin fragment with one small positive phase 2.
Compounds5
Best gradeB Thymosin α1
Approved medicines2 of 5
Prohibited in sport3 of 5

What this family is

Thymosin α1 is a 28-amino-acid peptide from the thymus that pushes T-cells and dendritic cells toward a stronger antiviral response. It has been sold as Zadaxin for hepatitis B and as an immune adjunct in China, Italy and around thirty other countries since the 1990s. LL-37 is the only cathelicidin humans make: a 37-amino-acid antimicrobial produced by skin, gut and immune cells that kills bacteria and signals repair. VIP is a 28-amino-acid hormone that relaxes vessels and airways and dampens inflammation, licensed narrowly for erectile dysfunction and promoted online as a nasal spray for 'mould illness'. ARA-290 is an eleven-amino-acid piece of erythropoietin that keeps its tissue-repair signal and drops its red-cell signal. Thymalin is a calf-thymus peptide extract registered in Russia since 1982, sold online as an immune and longevity 'bioregulator'.

Thymosin α1's evidence is substantial and mixed. Twenty-plus randomised trials support the hepatitis indications; the largest trial ever run on it — 1,106 adults with sepsis, published in the BMJ in 2025 — found no reduction in 28-day mortality. LL-37's human evidence is two randomised trials of a topical gel on venous leg ulcers: a 34-patient study that found faster healing and a 148-patient study that did not, except in large wounds. Nothing supports the injected 'immune' use sold online, and injected LL-37 is pro-inflammatory in the laboratory. VIP's largest trial — intravenous aviptadil in 461 patients with COVID-19 respiratory failure — was stopped for futility, and its nasal 'mould illness' use has no trial at all. ARA-290's 64-person phase 2 moved a nerve-fibre surrogate at one dose while pain improved equally on placebo. Thymalin's longevity claim rests on one St Petersburg series of 266 elderly people with no randomisation or blinding described.

None is approved in the US or EU-wide; VIP with phentolamine is licensed in the UK and a few countries for erectile dysfunction. LL-37, ARA-290 and injected VIP for other uses are prohibited in sport under the non-approved-substances rule.

Grade counts across the family: 0 × A · 2 × B · 3 × C · 0 × D. The best grade here, B, means probable, not settled. How LYO grades →

The compounds, graded

Every member with its best-supported outcome grade, human-trial count and regulatory status. Each opens the full evidence page.

Thymosin α1

B

Immune-modulating thymic peptide. Approved in China and ~30 other countries; failed its largest trial.

Human trials20+ RCTs
StatusApproved outside US/EU (Zadaxin)

LL-37

C

The human cathelicidin antimicrobial peptide. Two randomised wound-healing trials; not approved.

Human trials2 RCTs (topical)
StatusNot approved

VIP (vasoactive intestinal peptide)

B

A 28-amino-acid gut and nerve hormone. Licensed in a few countries for erectile dysfunction; a 461-person COVID trial found nothing; sold as a nasal spray for 'mould illness' with no trial at all.

Human trialsTESICO RCT (n=461) + earlier sponsor RCT; small trials in ED and pulmonary hypertension
StatusLicensed narrowly (ED, some countries); other uses unapproved

ARA-290 (cibinetide)

C

An 11-amino-acid fragment of erythropoietin that repairs without raising red cells. A real phase 2 in a rare neuropathy; sold online for everything else.

Human trialsPhase 2 RCTs in sarcoidosis neuropathy (n=64) and diabetes; no phase 3
StatusNot approved; investigational

Thymalin

C

A calf-thymus peptide extract registered in Russia since the 1980s. Its longevity claim rests on one St Petersburg series without randomisation or blinding.

Human trials1 uncontrolled long-term series (n=266); Russian reports
StatusNot approved (Russia only)

Questions

Is thymosin alpha-1 approved?
In China, Italy and around thirty other countries, mainly for hepatitis B and as an adjunct. Not in the US, EU-wide or UK. Its largest trial, in sepsis, was negative.
Is thymalin the same as thymosin alpha-1?
No. Thymosin α1 is a defined peptide with twenty-plus randomised trials; thymalin is an undefined extract with one uncontrolled series.
Is LL-37 the same as TB-500?
No. TB-500 is a fragment of thymosin beta-4, a cell-migration protein; LL-37 is a cathelicidin antimicrobial. Thymosin α1, in this family, is a third, unrelated thymic peptide. The shared 'thymosin' name covers different proteins.
Did VIP work for COVID-19?
No. The NIH-run TESICO trial of 461 patients was stopped for futility, with no improvement in recovery or survival.
Does LL-37 help wounds heal?
As a topical gel on venous leg ulcers, a small trial said yes and a larger one said no except in large wounds. That is the entire human evidence. Injected use has none.

Written and maintained by LYO Research — how pages are written and checked. Reviewed 23 September 2026. Grades count human evidence only. Not medical advice. Correct this page →