LL-37: Side Effects & Safety

LL-37 is an endogenous human peptide, but exogenous administration at research doses raises the concentration well above physiological levels. The most important safety consideration is LL-37's dose-dependent switch from anti-inflammatory to pro-inflammatory activity — at low concentrations it modulates immunity, but at high concentrations it can drive excessive inflammation.

• Injection site reactions: Redness, warmth, and irritation at the injection site — can be more pronounced than with other peptides due to LL-37's immune-activating properties
• Localized inflammation: Transient swelling or inflammatory response at the injection site
• Fatigue: Immune activation can produce transient fatigue, similar to a mild immune response
• Low-grade fever: Rare, but reported with higher doses due to cytokine release

Critical considerations for LL-37:

• Pro-inflammatory potential: At concentrations above the therapeutic range, LL-37 can trigger excessive inflammatory responses. Dose accuracy is particularly important
• Autoimmune associations: Elevated LL-37 has been associated with autoimmune conditions including psoriasis (where it triggers plasmacytoid dendritic cell activation via TLR9) and lupus. Individuals with autoimmune conditions should exercise particular caution
• Stability: LL-37 can aggregate and lose activity, making quality control and proper storage essential
• Limited human data: Most safety data comes from observational studies of endogenous LL-37 levels and in vitro/animal research

• Autoimmune conditions, particularly psoriasis and lupus
• Chronic inflammatory conditions
• Pregnancy and breastfeeding
• Known hypersensitivity

Return to the LL-37 overview for general information.