LL-37: A Tracking Guide for the Cathelicidin Peptide

LL-37 is a 37-amino-acid cathelicidin peptide and one of the main antimicrobial peptides produced by the human innate immune system. It is also one of the more speculative peptides in self-experimentation circles, because the gap between the basic science and the clinical human data is wide.

What it does

LL-37 has direct antimicrobial activity against bacteria, some viruses, and some fungi in vitro. It also modulates innate immune signaling, influences inflammation, and has been studied in chronic infection, wound healing, and dysbiosis contexts. Endogenous LL-37 is produced from the hCAP-18 precursor by cells including neutrophils and epithelial cells.

The translation from in vitro and animal data to systemic injectable use in humans is where the evidence thins out considerably.

Typical protocol shape

Most self-experimentation protocols involve subcutaneous injection on a daily or every-other-day schedule for a defined block of weeks. Some users discuss nebulized administration for respiratory contexts. Sourcing and purity vary substantially, and LL-37 is one of the peptides where third-party testing is especially worth caring about.

What to track daily

• Injection time, dose, route, and site
• Any flushing, fatigue, or flu-like symptoms post-injection, which are commonly reported
• Sleep quality
• Energy on a 1 to 10 scale
• The specific symptom or infection you started it for, scored consistently
• Heart rate and temperature, especially in the first week

What to track weekly

• Weight
• Average symptom score
• Any new symptoms or rashes
• For chronic infection contexts: any specific markers your clinician is following

Bloodwork worth doing

• CBC with differential
• CMP for liver and kidney function
• hs-CRP and ESR for inflammation
• Any infection-specific labs relevant to your indication
• Baseline before starting is non-negotiable

Realistic expectations

The honest expectation is that LL-37 is a research peptide with limited well-controlled human data outside specific clinical studies. Some users report meaningful improvement in chronic symptoms; others report flu-like reactions and discontinue. The literature does not currently support promising it will resolve any particular condition.

It is also worth noting that LL-37 has been studied in both protective and pathogenic contexts, including some autoimmune associations, which is a reason to be conservative.

Common mistakes

• Starting at a high dose and triggering an aggressive immune-style reaction
• Using it for vague symptoms without a diagnostic workup
• Sourcing from suppliers without third-party testing
• Combining it with other immune-modulating compounds and being unable to attribute reactions
• Ignoring the flu-like reaction as "die-off" without considering it might be a signal to stop

A tracking template

Per dose: timestamp, route, amount, site. Per day: symptom score, energy, sleep, side effects, temperature. Per week: weight, average scores, new symptoms. Per cycle: CBC, CMP, inflammatory markers. Peptid AI will hold the daily side-effect log alongside dose so you can see whether reactions are titrating down over time or persisting.

Safety notes

LL-37 is one of the peptides where conservative dosing, slow titration, and active medical involvement are most warranted. If you develop persistent fever, rash, or any new autoimmune-style symptoms, stop and get evaluated. The downside of being cautious here is small. The downside of pushing through warning signs is not.

Peptid AI is an educational and self-tracking tool. Nothing in this post is medical advice. Doses mentioned reflect what is commonly reported in research literature — they are not recommendations. Always consult a qualified physician before starting, changing, or stopping any protocol.