What are the side effects of LL-37?
The most commonly reported LL-37 side effects are mild flu-like symptoms early, injection-site irritation, mast-cell activation in sensitive users. Most are mild and tend to be dose dependent. It is generally avoided with mast cell activation syndrome (MCAS). Human clinical evidence for LL-37 is limited, so this reflects reported and observed effects, not a complete safety profile.
Reported LL-37 side effects
- Mild flu-like symptoms early
- Injection-site irritation
- Mast-cell activation in sensitive users
Who should avoid it
- Mast cell activation syndrome (MCAS)
- Pregnancy / nursing
Bloodwork worth tracking
- CBC if running long courses
References
- LL-37, the truncation product of cathelicidin, antimicrobial review — Wang G, Curr Top Med Chem, 2020
- Human antimicrobial/host defense peptide LL-37 may prevent the spread of a local infection through multiple mechanisms: an update — Svensson D et al., Inflammation Research, 2025
- Significance of the LL-37 Peptide Delivered from Human Cathelicidin in the Pathogenesis, Treatment, and Diagnosis of Sepsis — Mankowska A et al., Archivum Immunologiae et Therapiae Experimentalis, 2025
Pepdex is an editorial reference, not medical advice. Peptides vary in legal and approval status by country, many are research compounds without full human safety data. Talk to a qualified clinician before starting anything.
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Last updated 2026-06-06.