Thymosin beta-4 vs LL-37
It is sold as an injection to heal tendon, muscle and joint injuries. No one has tested that use in people; the small human trials are on eye drops, the heart and safety. It is sold as an injected natural antibiotic and healer. The only trials used it on skin sores and gave mixed results, and injecting it has never been studied in people.
Thymosin beta-4 has the stronger evidence, grade B (some human evidence) against grade C for LL-37. Neither is FDA approved.
Evidence
BSome human evidence
CAnimal and cell studies
Human studies cited
Animal or cell studies cited
Why the grade
Thymosin beta-4 has two phase 1 safety trials in healthy volunteers (40 and 84 subjects), an 18-patient phase 3 eye-drop trial, a 96-patient randomized trial after heart attack, and a venous ulcer study. All are small and most tested topical or intravenous full-length protein for specific diseases, not the injected wound-healing use it is sold for. Animal work in rats and mice supports wound and cardiac effects. Grade B for the clinical indications under study; the injury-recovery use sold online has no trial.
Two randomized placebo-controlled trials exist, both of LL-37 applied topically to chronic wounds: 148 patients with venous leg ulcers (negative on the primary endpoint) and a smaller diabetic foot ulcer trial. The injected 'immune support' use sold online has no human data at all. The rest of the human literature is observational work on the body's own LL-37 in wounds, psoriasis, and rosacea, plus cell and mouse mechanism studies. For the use it is sold for, that is C.
FDA
Not approved
Thymosin beta-4 is not approved by the FDA for any use. Injectable products sold online, often labeled TB-500 (which the FDA reviewed as a seven-amino-acid fragment), are research chemicals; the FDA found no human exposure data for TB-500, and the agency has not acted on its compounding advisory committee's July 2026 vote to recommend adding TB-500 to the 503A bulks list. RGN-259 eye drops are in a phase 3 trial for neurotrophic keratopathy, and a recombinant intravenous form has been tested in heart attack patients.
Not approved
Not approved by the FDA for any use and sold as a research chemical. LL-37 was nominated for the FDA's compounding bulk-substances list and placed in Category 2 (significant safety risk); the nomination was withdrawn, the FDA removed it from the category in April 2026, and a Pharmacy Compounding Advisory Committee review is planned before the end of February 2027.
Sold for
Thymosin beta-4 is sold as a regenerative injection for tendon, muscle and joint injuries and promoted as the full-length version of TB-500.
LL-37 is sold as an injectable 'natural antibiotic' that fights infections, breaks up biofilms, heals wounds, and modulates immunity.
Studies say
Small randomized trials show safety and signals of benefit in eye and heart disease, but the injected use for sports injuries has never been tested in people, which is why it grades B for the studied indications and no better.
Topical LL-37 has two small wound-healing trials with mixed results, the body's own LL-37 is well studied and drives inflammation in psoriasis and rosacea, and there are no human data on injecting it, so the evidence for the marketed use is grade C.
Class
Actin-regulating peptide
Host-defense antimicrobial peptide
Route
Several routes
Injection