# LL-37

Endogenous antimicrobial peptide for chronic infections/dysbiosis; pro-inflammatory, pro-tumour in places.

- Page: https://peprank.xyz/peptides/ll-37
- Category: Immune (Research peptide)
- Also known as: cathelicidin; hCAP-18 C-terminal peptide; CAP-18
- Routes: Topical / Injection
- Sequence: LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES (none (cathelicidin, CAMP C-terminus))
- Safety tier: Strict: Avoid · Balanced: Caution · Evidence only: Caution
- Risk axes (0 none to 3 severe): Seen harm 1, Mechanism 2, Data gap 3, Silent harm 2, Product 3
- Positive: 53% of 26 graded reports glowing or positive, shrunk toward the 49% all-report average by 8 reports' weight
- Rank: #30 of 61 research peptides
- Graded reports: 26 (Glowing 4, Positive 10, Mixed 4, Nothing 2, Negative 4, Bad reaction 2)
- Evidence: Small human studies — Topical phase 2 for venous leg ulcers; injectable use animal only
- Access: Grey market
- Onset: Die-off or Herxheimer-type aches often start within hours of the first doses; reported benefits on infections or gut symptoms come over 1-5 weeks.
- Lasts: Short-lived in the body (minutes to hours); taken daily or twice daily in 20-50 day courses, often 30 days on and 30 off.
- Cost per month: ≈ €45–110 (researchers' estimate)
- Updated: 2026-10-30

**Why Avoid under the strict bar:** Pro-inflammatory/autoimmune and context-dependent pro-tumour activity, plus FDA-noted reproductive effects.

## What users report

There are few reports. Some credit it with clearing long-running low-grade infections or cellulitis alongside antibiotics, or with dysbiosis. Others feel 'off' with worst-ever brain fog or Herxheimer-type reactions, and many keep it only for acute illness because of the risks discussed.

**Effects:** clearing stubborn infections (anecdotal); biofilm/dysbiosis claims; wound healing (topical)

**Downsides:** brain fog, malaise; Herxheimer-type flu-like reactions; injection-site inflammation

**Risks:** Pro-tumorigenic in ovarian, breast and lung cancer models (FDA note); Drives autoimmune inflammation (psoriasis, lupus) and is found in atherosclerotic plaque; FDA: nonclinical detrimental effects on male reproduction

**Typical use:** 100-250 mcg/day subQ in short courses.

**Getting it:** Research-peptide vendors only; on the FDA's Category 2 list, so US pharmacies cannot compound it, and users report it getting harder to find. No approved product anywhere.

**Stacked with:** Thymosin alpha-1 (The usual partner in Lyme and mould protocols, taken to support immunity while LL-37 is the antimicrobial; also what users credit for some of the die-off.); BPC-157 and KPV (Gut stacks for SIBO, H. pylori and candida; users who improved on these stacks cannot separate the peptides.); Binders (charcoal, zeolite, cholestyramine) (Taken to blunt die-off reactions, alongside a lower starting dose.)

## Risk profile

- **Seen harm 1/3:** Of the three people ever injected with it in a trial, one developed a keratoacanthoma-like skin proliferation that cleared after stopping; topical trials saw more local reactions at the highest dose, and one first-hand report describes a face swollen shut for a week. Isolated.
- **Mechanism 2/3:** Immune activation that is established in humans: LL-37 is a T-cell autoantigen in nearly half of psoriasis patients and helps drive lupus by delivering self-DNA to dendritic cells. Pro-tumour data come only from blocking or knocking out the endogenous peptide, and FDA notes male reproductive effects in animals.
- **Data gap 3/3:** Topical trials cover about 180 people, but there is no human safety data for the subcutaneous injection people use beyond three intratumoral melanoma patients.
- **Silent harm 2/3:** Autoimmune disease would build up over weeks to months, though its skin, joint and blood signs are detectable.
- **Product 3/3:** Grey-market injectable vials only; it is on FDA's risk list, so US pharmacies cannot compound it.
- **Never if:** Psoriasis, lupus or other autoimmune disease; Active cancer or a history of cancer; Trying to conceive (male reproductive effects in animals); Pregnancy or breastfeeding (no human reproductive data)

## Top reports

- Glowing, immune: “Antibiotics were working, introduce the LL-37 and within 3 weeks the infection cleared. I used it on half dose to avoid a bad flu that was going round but it cleared up my athletes foot like no other cream before, 3 months in and I'm still all clear” — [r/Peptidesource](https://www.reddit.com/r/Peptidesource/comments/1qo5isf/anyone_tried_ll37/o21zxc9/)
- Glowing, gut: “Killed all the nad crap. Was a rough ride for 5 weeks. Tongue got pink again, no more bloating and all the other crap that comes with h pylori , sibo and candida” — [r/SIBO](https://www.reddit.com/r/SIBO/comments/dv4vq5/xpost_from_rpeptides_peptide_ll37_for_treating/mvuwedk/)
- Glowing, gut, 500 mcg/day: “Healed my Bad breath that i had for 14 years. Did keto and ll-37. im kind of in the State to start a second course because i reintroduced way to fast” — [r/Candida](https://www.reddit.com/r/Candida/comments/y4hbbh/ll37_for_treating_candida/iziw5a7/)
- Glowing, immune, 200 mcg/day: “Helped me to cure chronic sinusitis, I was so tired of using antibiotics every month! Used in spray, 200 mcg daily, reconstituted with colloid silver water” — [r/SIBO](https://www.reddit.com/r/SIBO/comments/1m2xpq8/ll37_recommendations_or_experiences/nd8km77/)
- Positive, immune: “I’ve had some luck with controlling my outbreaks with peptide therapy, specifically LL-37.” — [r/Herpes](https://www.reddit.com/r/Herpes/comments/1qa0wga/ll37_peptide/)

## Cheapest in Europe

- [Modern Peptides EU](https://modernpeptides.eu/product/ll-37/) (DE): LL-37 5mg, €58, €12/mg
- [Particle Peptides](https://particlepeptides.com/en/buy-peptides/94-ll-37-5mg.html) (SK): LL-37 5mg, €78, €16/mg

## Studies

- [Grönberg et al. 2014: topical LL-37 for hard-to-heal venous leg ulcers, first-in-man randomised placebo-controlled trial](https://pubmed.ncbi.nlm.nih.gov/25041740/) (rct, n=34, 2014): Topical LL-37 at 0.5 mg/mL healed ulcers about six times faster than placebo over 4 weeks, with no local or systemic safety concerns.
- [Mahlapuu et al. 2021 (HEAL LL-37): phase IIb multicentre trial of topical LL-37 in venous leg ulcers](https://pubmed.ncbi.nlm.nih.gov/34687253/) (rct, n=148, 2021): Failed its primary endpoint: no healing benefit over placebo in the full population; only a post hoc subgroup with large ulcers improved.
- [Lande et al. 2007: plasmacytoid dendritic cells sense self-DNA coupled with LL-37](https://pubmed.ncbi.nlm.nih.gov/17873860/) (in-vitro, 2007): LL-37 binds the body's own DNA and turns it into an interferon trigger, a key driver of psoriasis; the basis of its autoimmune concern.
- [Coffelt et al. 2009: the pro-inflammatory peptide LL-37 promotes ovarian tumour progression](https://pubmed.ncbi.nlm.nih.gov/19234121/) (animal, 2009): LL-37 recruited stromal cells and increased ovarian tumour growth and vascularisation in mouse xenografts.
- [Chen et al. 2018: roles and mechanisms of human cathelicidin LL-37 in cancer](https://pubmed.ncbi.nlm.nih.gov/29843147/) (review, 2018): LL-37 promotes ovarian, lung, breast, prostate, pancreatic and skin cancers in models but suppresses colon and gastric cancer; effects are tissue-specific.
- [Kahlenberg & Kaplan 2013: the role of LL-37 in inflammation and autoimmune disease](https://pubmed.ncbi.nlm.nih.gov/24185823/) (review, 2013): LL-37 is overexpressed in psoriasis, lupus, rheumatoid arthritis and atherosclerosis, where it amplifies inflammation as well as fighting microbes.

## Sources

- [Roles and mechanisms of human cathelicidin LL-37 in cancer (Cell Physiol Biochem 2018)](https://doi.org/10.1159/000490183)
- [FDA risk note on cathelicidin LL-37](https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks)