LL-37

What is it?

LL-37 is a 37-building-block peptide your own body makes. White blood cells and skin make it to punch holes in germs. Its name comes from its first two building blocks (two leucines, "LL") and its length. The LL-37 sold online is made in a lab.

Why do people use it?

Online, people use it hoping to fight long infections, heal wounds or calm the gut. In science, it was mostly tested as a cream or solution put right on stubborn skin sores.

Does it really work?

Not proven. On leg sores, a small trial looked hopeful, but a bigger 148-person trial found no overall benefit. A small foot ulcer study saw better new tissue but did not lower germs or swelling markers. We found no trial of LL-37 shots for infections or the gut.

Studies in people

Only 3 small human treatment studies found, all on skin sores. None tested shots.

We read each of these 3 papers on PubMed on October 28, 2026.

Is it safe? Side effects

• The FDA says it does not have enough safety facts about LL-37 in people.
• The FDA says lab and animal research suggests LL-37 may hurt male fertility and may help tumors grow in some body parts.
• A foot sore study did not show clearly fewer germs, so "germ-killing" claims are not proven in people.
• Shots sold online were never tested in people.

Is it legal in the US?

LL-37 is not an FDA-approved medicine.

• The FDA had put LL-37 on its "Category 2" list of risky pharmacy ingredients.
• In April 2026, it was moved off that list because the groups that asked about it withdrew their request. The FDA did not say it is safe.
• It is also not on the list regular pharmacies may use.
• On October 28, 2026, HHS issued a peptide policy for 6 other peptides. It does not cover LL-37.

What this means for LL-37

• Leaving Category 2 is not approval. The FDA said it did not judge it safe. (FDA)
• Vials sold "for research" are not medicine. The FDA has warned sellers of such products. (FDA)
• Bringing it into the US for yourself is, in most cases, illegal, the FDA says. (FDA)

Banned in sports? Drug tests

Not named, but may be banned.

LL-37 is not named on WADA's list. But WADA says its list is not complete. It also bans any drug that is not approved for people by any government anywhere (section S0). From Jan 1, 2027, that rule names "peptides" too. Ask USADA before you use it.

Check work, NCAA, and military rules for LL-37

Talk to your doctor

If you have a wound that will not heal or an infection that keeps coming back, see a doctor. These need a real cause found, like poor blood flow or diabetes. We never share doses or tell you where to buy. Print our doctor questions sheet.