LL-37: Reference Overview and Reconstitution Notes

July 9, 2026

LL-37

What it is

LL-37 is the only known human member of the cathelicidin family of antimicrobial peptides. It is a 37-amino-acid, cationic, amphipathic peptide released from the C-terminal end of the hCAP18 precursor protein and produced by neutrophils, epithelial cells, and other cells as part of innate immune defense.

Research context and categorization

LL-37 is generally grouped under the immune and host-defense category of research peptides, and it is also discussed in relation to healing and tissue repair. In neutral research terms, it is investigated for its broad in vitro antimicrobial activity against Gram-positive and Gram-negative bacteria, some viruses, and fungi, and it is studied in the context of biofilm disruption. It is commonly discussed in relation to immune signaling and inflammatory modulation, and it is investigated for wound-repair-associated processes such as keratinocyte migration, angiogenesis, and epithelial proliferation in laboratory and preclinical models. These uses are investigational. LL-37 is not an approved therapy for any of these applications, and the effects described are studied in models rather than confirmed as established benefits in humans. Research literature also notes practical hurdles for any applied use, including limited proteolytic stability and cytotoxicity at higher concentrations, which is one reason much work focuses on modified analogs rather than the native peptide.

Status

Regulatory status: Research-only. LL-37 is not FDA-approved and has no formal FDA classification for therapeutic or compounding use. It is considered an investigational compound.
Sport status: Not specifically listed by name on the WADA Prohibited List. However, WADA's S0 category ("non-approved substances") is a catch-all covering any pharmacological substance not currently approved by a government regulatory authority for human therapeutic use, so an unapproved peptide like LL-37 can fall under that broad prohibition. Anyone subject to testing should confirm current status with their governing body.

Reconstitution notes (general)

Lyophilized peptide is typically reconstituted with bacteriostatic water. The resulting concentration equals the milligrams of peptide in the vial divided by the millilitres of bacteriostatic water added. For example, the same amount of powder in a larger volume yields a lower concentration, while a smaller volume yields a higher concentration. To work out a target concentration for any vial size, use the reconstitution calculator at /pages/tools.

Dilution and handling notes (compound-specific)

LL-37 is supplied as a lyophilized powder and is freely soluble in water, so it generally dissolves in bacteriostatic water without much difficulty. That said, it is a surface-active, aggregation-prone peptide, so a few compound-specific points apply. It carries a strong net positive charge, and in low-salt water electrostatic repulsion between molecules helps keep it dissolved, whereas high ionic strength or high concentration screens that charge and can promote peptide-to-peptide clumping, haze, or precipitation. Reference handling therefore tends to favour the dilute side; published laboratory and early-phase topical work has used relatively low concentrations, on the order of roughly 0.5 to 1.6 mg/mL, which reflects both adequate solubility at those levels and concentration-dependent cytotoxicity being a concern higher up. The usual fixes if cloudiness appears are to reconstitute at a lower concentration and to use a low-salt diluent rather than concentrated saline buffers. Two further quirks: as a cationic amphipathic peptide it can adsorb onto glass and plastic surfaces, which can lower the effective amount in very dilute preparations, so low-binding labware is often preferred; and it foams easily, so direct the diluent slowly down the inside wall of the vial rather than onto the powder, swirl gently rather than shaking, and avoid repeated freeze-thaw cycles. Structurally, LL-37 is largely unstructured in plain aqueous solution and only folds into its curved alpha-helical shape in membrane-mimetic environments, a common note in the biophysical literature.

Handling and storage

Refrigerate the reconstituted vial at 2 to 8 degrees Celsius and keep it out of direct light. Wipe the stopper with an alcohol swab before each access, and label the vial with the mix date. A reconstituted, refrigerated peptide is commonly treated as usable for about four weeks. Discard the solution if it becomes cloudy or discolored, or if visible particles or floaters appear.

Tools and supplies

For laboratory and research reference only. Educational content, not medical, dosing, injection, or therapeutic guidance, and not intended for human or animal use. Any research uses described are investigational and not confirmed or approved benefits. Confirm anything involving health with a licensed professional. References linked above.