- Last reviewed
- 29 Apr 2026
- Sources cited
- 7
- Residues
- 37
LL-37
Last verified: 2026-04-29
At a glance
| Also known as | Cathelicidin LL-37, hCAP-18(134-170), human cathelicidin antimicrobial peptide |
| Class | Endogenous human antimicrobial peptide (AMP) — α-helical cathelicidin family member |
| Typical route | Subcutaneous injection, daily during active treatment cycles |
| Half-life | Short — minutes in plasma; tissue effects persist longer through immunomodulatory action |
| Molecular weight | 4,493 Da |
| Sequence | Leu-Leu-Gly-Asp-Phe-Phe-Arg-Lys-Ser-Lys-Glu-Lys-Ile-Gly-Lys-Glu-Phe-Lys-Arg-Ile-Val-Gln-Arg-Ile-Lys-Asp-Phe-Leu-Arg-Asn-Leu-Val-Pro-Arg-Thr-Glu-Ser (37 amino acids — the only known human cathelicidin, derived by proteolytic cleavage of hCAP-18) |
| UK status | Not approved as a licensed medicine. Sold as a research chemical. |
| US status | Not FDA-approved. Not DEA-controlled. Sold as a research chemical labelled “not for human consumption.” |
What it is
LL-37 is the only human cathelicidin — an endogenous antimicrobial peptide produced naturally by epithelial cells, neutrophils, macrophages, and other immune cells as part of innate immunity. It is distinguished from most compounds in this encyclopedia by being a molecule the body already makes: synthetic LL-37 is a copy of an endogenous peptide, not a designer drug.
The peptide acts in two distinct modes:
- Direct antimicrobial activity — kills bacteria, fungi, and viruses through membrane disruption, with documented activity against 38+ bacterial species, 16+ fungi, and 16+ viruses
- Immune modulation — recruits immune cells, modulates inflammation, promotes wound healing, and disrupts biofilms
The biohacker / chronic-illness community uses synthetic LL-37 primarily for chronic infection support — particularly chronic Lyme disease and persistent infection profiles where conventional antibiotics have failed against biofilm-protected organisms. The mechanism is genuinely relevant: LL-37 has demonstrated ability to disrupt bacterial biofilms (the protective matrix that makes chronic infections drug-resistant) and to penetrate persister-form Borrelia burgdorferi in laboratory studies. This is the central audience for LL-37 in the context of this encyclopedia.
The clinical reality is that no controlled human trials of synthetic LL-37 in chronic infection or biohacker contexts have been published. All human use is extrapolation from laboratory and animal data, plus practitioner experience in chronic-illness clinics. The compound exists in the same evidence-thin grey zone as ipamorelin and 5-Amino-1MQ, with the mechanistic case being plausible but the controlled human evidence essentially absent.
Mechanism
LL-37 has two functional modes that operate simultaneously:15
Direct antimicrobial activity (membrane disruption)
The peptide is cationic and amphipathic — positively charged with hydrophilic and hydrophobic faces — which lets it bind preferentially to negatively-charged microbial membranes. On binding, LL-37 inserts into the membrane and forms transmembrane pores that disrupt membrane integrity and cause cell death.
Documented spectrum:
- Gram-positive bacteria: Staphylococcus aureus (including MRSA), Streptococcus pyogenes, Enterococcus
- Gram-negative bacteria: Escherichia coli, Pseudomonas aeruginosa, Klebsiella
- Spirochetes: Borrelia burgdorferi (Lyme), Treponema pallidum
- Fungi: Candida albicans, dermatophytes
- Viruses: enveloped viruses including HIV, HSV, influenza
- Mycobacteria: limited activity against Mycobacterium tuberculosis
Immune modulation
Independent of direct antimicrobial action, LL-37 modulates immune function:
- Recruits immune cells (neutrophils, monocytes, T cells) through chemokine-like activity
- Modulates cytokine production — generally pro-inflammatory in acute settings, can be anti-inflammatory in chronic settings
- Promotes angiogenesis and re-epithelialisation — wound healing
- Disrupts biofilm formation — particularly relevant for chronic infections protected by biofilm
Anti-biofilm activity (the central biohacker claim)
Bacterial biofilms are protective matrices that shield organisms from both antibiotics and the host immune system. LL-37 disrupts biofilm formation at concentrations below what’s needed for direct membrane killing, and can penetrate established biofilms to reach the protected organisms. This is the mechanistic basis for its use in chronic Lyme protocols and other persistent-infection contexts where conventional antibiotics struggle.
The biofilm activity is well-documented in vitro. Translation to chronic-infection treatment outcomes in humans is the unstudied question.
Routes of administration
Subcutaneous injection (the standard route)
| Bioavailability | Sufficient for local immune-modulatory effects; systemic plasma levels are short-lived |
| Onset | Immune-modulatory effects may persist beyond plasma clearance through downstream cytokine cascades |
| Duration | Plasma half-life is short (minutes); functional effects can last hours-to-days through immune activation |
| Typical dose | 100–500 mcg subQ daily during active treatment cycles |
| Equipment | Insulin syringe (29G–31G, U-100), bacteriostatic water, alcohol wipes |
| When this route makes sense | Default for systemic immune effects. |
Topical (for wound and skin applications)
LL-37 has been studied topically for chronic wound healing and skin infections. Topical application is the most clinically-supported use case but is not the typical biohacker pattern.
Oral, sublingual, intranasal
Oral is not viable — LL-37 is GI-degraded. Sublingual and intranasal absorption are unreliable for a 37-residue peptide. Some research-chem vendors sell oral capsules; these have negligible expected systemic effect.
Cross-route comparison
SubQ for systemic use; topical for wound and skin applications. Most biohacker / chronic-illness use is subQ daily during active treatment cycles.
What the evidence says
Honest summary: LL-37 is a well-characterised endogenous antimicrobial peptide with documented in-vitro activity against a broad spectrum of pathogens including biofilm-protected forms. The mechanistic case for its use in chronic infections is reasonable. There are no controlled human clinical trials of synthetic LL-37 in chronic Lyme, MCAS, or biohacker applications. Practitioner reports in chronic-illness clinics suggest some users benefit; the evidence is anecdotal and uncontrolled.
Antimicrobial spectrum (well-supported in vitro)
The broad-spectrum antimicrobial activity is well-documented in laboratory studies:17
- Activity against bacterial, fungal, and viral pathogens
- Anti-biofilm activity at sub-MIC concentrations
- Activity against drug-resistant organisms including MRSA
Borrelia / Lyme activity (in vitro)
Multiple in-vitro studies have demonstrated LL-37 activity against:
- Spirochete forms of Borrelia burgdorferi
- Persister forms (a key target for chronic Lyme treatment)
- Biofilm-encased Borrelia populations
This is the mechanistic foundation for the chronic-Lyme use case.
Wound healing (limited clinical evidence)
Topical LL-37 has been investigated for chronic wound healing, including diabetic ulcers and pressure ulcers. The evidence is emerging but not yet at the level of FDA-approval trials.
Chronic Lyme / persistent infection (no controlled clinical evidence)
No published controlled human trials exist for systemic LL-37 in chronic Lyme, post-treatment Lyme disease syndrome, or persistent infection contexts. Use is based on:
- The in-vitro mechanism
- Practitioner experience in chronic-illness clinics
- Patient anecdotal reports
MCAS / immune modulation (unstudied directly)
LL-37 itself has documented immune-modulatory effects, but its use in MCAS specifically is not supported by controlled studies. Some practitioner protocols include LL-37 for chronic-infection MCAS profiles, with the claim that addressing underlying chronic infections may reduce MCAS triggers. The mechanism is plausible; the controlled evidence is absent.
What the evidence does NOT show
- No controlled human trials in chronic Lyme, MCAS, biohacker, or longevity contexts
- No characterised dose-response in humans for systemic administration
- No long-term safety data at any dose level
- No comparative effectiveness data vs antibiotics, herbal protocols, or other chronic-infection interventions
Typical use patterns
Standard biohacker / chronic-infection protocol
- 100–500 mcg subQ daily during active treatment cycles
- Cycles of 4–8 weeks on, 4 weeks off
- Often combined with other antimicrobial peptides, antibiotics, or anti-inflammatory compounds
- Some practitioners pulse-dose (every other day) rather than continuous daily
Chronic Lyme protocols
LL-37 is commonly included in chronic Lyme treatment alongside conventional antibiotics, anti-inflammatory peptides (like KPV), and biofilm-disrupting protocols (enzymes, herbs). Specific dose conventions vary by practitioner; doses tend to start lower (100–200 mcg) and titrate up based on Herxheimer-style reactions, which are common when biofilm disruption releases bacterial debris.
Sensitive-start protocol
- 50–100 mcg subQ daily for the first 1–2 weeks
- Hold at the start dose; assess for Herxheimer reactions, autoimmune flare, or other immune-activation signals
- Sensitive users in this audience commonly need slower ramps than the general biohacker population
Stacking
- KPV — common pairing in chronic-infection / MCAS protocols. Mechanistically complementary (LL-37 directly antimicrobial; KPV anti-inflammatory and mast-cell-stabilising).
- BPC-157 — common pairing for tissue-repair component of chronic illness.
- Antibiotics — often combined in supervised chronic-infection protocols. LL-37 may sensitise biofilm-protected organisms to antibiotics.
- Antifungal protocols — LL-37 has activity against Candida and other fungi.
- Other AMPs (defensins, others) — limited research; not standard practice.
Why a user might choose LL-37
- Documented biofilm disruption activity
- Activity against Borrelia persister forms
- Endogenous peptide — less foreign than designer compounds; mechanism is “more of what your body already does”
- Targeted at chronic-infection profiles that don’t respond to conventional antibiotics
Why a user might be cautious
- Autoimmune flare risk — LL-37’s immune-activating effects can worsen autoimmune disease in some users
- Herxheimer reactions — biofilm disruption releases bacterial debris and can produce significant flu-like symptoms
- Absence of controlled human evidence — the use case rests on mechanism and practitioner experience, not trials
For sensitive systems
LL-37 occupies an unusual position in the sensitive-systems framework: it has both plausible benefit (addressing chronic infections that drive sensitive-systems symptoms) and plausible harm (immune activation that can worsen autoimmune or MCAS profiles).
Start dose for sensitive users. 50–100 mcg subQ daily for 1–2 weeks. Hold at the start dose and assess. The audience for LL-37 substantially overlaps with the audience for whom sensitive-start dosing is most important — chronic Lyme, MCAS, autoimmune profiles.
Ramp. If 100 mcg is tolerated, gradually increase to 200–500 mcg over 4–6 weeks. Many sensitive users find sub-300 mcg sufficient.
Expected adjustment profile:
- Herxheimer-style reactions — flu-like symptoms, fatigue, brain fog, achiness, low-grade fever in the first 1–2 weeks. Typically reflects biofilm disruption and bacterial debris release. Common; can be significant.
- Injection-site reactions — pain, redness, induration. Common.
- Mild headache in the first few days
- Subjective immune-activation symptoms — sometimes described as feeling “fighting something off”
What’s not normal and warrants stopping: severe or worsening autoimmune flare, persistent fever, severe rash or hives suggesting allergic response, atypical chest sensations, difficulty breathing, severe Herxheimer reactions that don’t resolve within a few days.
For MCAS / histamine-sensitive users. Worth specific caution. LL-37 itself can activate mast cells in some users (the mechanism is not fully characterised but practitioner reports document occasional MCAS flares). Sensitive-start dosing is essential. Pre-loading with antihistamines (cetirizine, famotidine) before each dose is a common precaution. Pairing with KPV (which is mast-cell-stabilising) is a community-standard approach.
For autoimmune disease (lupus, RA, psoriasis, others). Strong relative contraindication. LL-37 has been documented to drive immune activation that can worsen autoimmune flares in susceptible users. Active autoimmune disease should be a “do not use without specialist input” signal for this compound.
For POTS users. No specific cardiovascular contraindication. Generally well-tolerated by POTS users when used in chronic-infection contexts.
For UARS / chronic fatigue / ME/CFS / chronic Lyme. This is the primary target audience for LL-37 in this encyclopedia’s framework. Many users in this population have chronic-infection components (Lyme, mycoplasma, EBV reactivation, gut dysbiosis). LL-37 is mechanistically targeted at exactly these issues. Worth a 4–8 week trial with sensitive-start dosing, careful Herxheimer monitoring, and ideally practitioner supervision.
For pregnancy and breastfeeding. No safety data; avoid.
Interactions worth considering:
- KPV — common synergistic pairing
- Antibiotics — may sensitise biofilm-protected organisms; common combination
- Immunosuppressants — theoretically antagonistic; consult prescriber
- Herbal antimicrobials (oregano, berberine, others) — common in chronic-Lyme protocols; no documented direct interactions
- No documented interactions with the GH cluster, GLP-1s, or the longevity peptides in this encyclopedia
Reasonable expectations
Onset. Herxheimer-style reactions, where they occur, typically appear within 1–7 days. Subjective improvement in chronic-infection symptoms — where it occurs — typically takes 4–12 weeks of consistent dosing.
Response rate. Highly variable. Some users in chronic-infection contexts report dramatic improvement; others report no measurable change. Without controlled trial data, the population-level response rate is genuinely unknown.
What the evidence actually supports.
- Broad-spectrum antimicrobial activity in vitro
- Biofilm disruption — well-documented mechanically
- Anti-Borrelia activity in vitro
- Wound healing in topical applications — emerging clinical evidence
What the evidence does not support.
- Specific clinical outcomes in chronic Lyme — no controlled trials
- MCAS treatment claims — not directly studied
- General “immune support” for healthy users — not the use case, not the audience the mechanism targets
What not to expect.
- Antibiotic-equivalent results. LL-37 is best-supported as an adjunct, not a replacement.
- Acute infection treatment. The compound’s use case is chronic, biofilm-protected infections, not acute ones.
- No Herxheimer reactions. If the compound is producing biofilm disruption, Herxheimer-type symptoms are expected, not unusual.
Cost
LL-37 is not available through licensed pharmacy channels.
Research-chemical UK market:
- 5 mg vials: ~£40–100
- 10 mg vials: ~£70–180
- Premium / lab-tested vendors: 30–50% premium
Monthly cost at 300 mcg/day, daily dosing: roughly £40–100/month, mid-range for research-chem peptides.
Sensitive-start economics. A user starting at 100 mcg/day uses one-third the standard dose. A 5 mg vial covers 50 doses, generally past the reconstituted shelf life — buy smaller vials or accept some product loss.
Quality variance
LL-37’s 37-residue length and amphipathic structure make synthesis quality more variable than for shorter peptides. Lab-tested vendors with mass-spec or HPLC certificates are essential — substituted or improperly synthesised LL-37 is functionally inactive.
Reconstitution
What’s in the box
Research-chemical LL-37 ships as lyophilised white powder in a glass vial, typically 5 mg or 10 mg per vial. Larger vials (15 mg, 25 mg) exist but are less common.
You’ll also need: BAC water, U-100 insulin syringe, larger transfer syringe, alcohol wipes.
The math
5 mg vial, 2 mL BAC water (the standard)
- Concentration: 2.5 mg/mL (2,500 mcg/mL)
- 100 mcg sensitive-start = 0.04 mL = 4 units
- 200 mcg = 0.08 mL = 8 units
- 300 mcg = 0.12 mL = 12 units
- 500 mcg = 0.2 mL = 20 units
5 mg vial, 5 mL BAC water (for very low / sensitive-start dosing)
- Concentration: 1 mg/mL (1,000 mcg/mL)
- 50 mcg = 0.05 mL = 5 units
- 100 mcg = 0.1 mL = 10 units
10 mg vial, 2 mL BAC water (for higher-dose protocols)
- Concentration: 5 mg/mL
- 500 mcg = 0.1 mL = 10 units
- 1 mg = 0.2 mL = 20 units
Reconstitution procedure
Same as the rest of the encyclopedia: alcohol-wipe stoppers, slow water injection down the vial side, no shaking, label vial, refrigerate.
Storage and stability
LL-37 reconstituted with BAC water is stable for ~14–28 days refrigerated — at the shorter end of the research-chem peptide range due to the peptide’s length and complexity.
- Conservative: 7–14 days
- Middle: 14–21 days
- Optimistic: ~28 days
The honest middle is 14 days at 2–8°C. Store at the back of the refrigerator. Do not freeze.
If you reconstitute with plain sterile water, the vial is single-use — discard within 24 hours.
For a 5 mg vial at 300 mcg/day: ~16 doses → 16 days, just past the conservative stability window. Plan vial timing carefully.
What gets miscalculated
- Treating LL-37 as a 28-day peptide. Stability is shorter; 14 days is the practical middle.
- Going too high too fast. Herxheimer reactions are dose-dependent; sensitive-start matters more for this compound than for many others.
- Skipping autoimmune screening. Active autoimmune disease is a relative contraindication that’s easily missed if not asked about.
- Not pre-loading antihistamines in MCAS users — meaningfully reduces flare risk.
Areas of concern ⚠
Autoimmune flare and immune activation
LL-37 can drive immune activation that worsens autoimmune disease in susceptible users. This is documented in practitioner experience and is mechanistically plausible (LL-37 is known to be elevated in some autoimmune conditions including psoriasis and lupus). For users with active autoimmune disease, strong relative contraindication.
Herxheimer reactions
Biofilm disruption releases bacterial debris and can produce significant Herxheimer-type flu-like symptoms. This is expected, not pathological — but it can be severe enough to require dose reduction or pausing. Sensitive-start dosing and slow ramping are the cautious approach.
Evidence gap
No controlled human trials of synthetic LL-37 in chronic-infection or biohacker applications. The evidence base is in-vitro studies, animal models, and practitioner experience. This is a fundamentally different evidence position than compounds with controlled human trials.
Long-term safety uncharacterised
No published long-term controlled studies. Mechanistic concerns from sustained immune activation:
- Theoretical autoimmune disease promotion
- Theoretical chronic inflammation
- Unknown effects of chronic supraphysiological LL-37 levels on the cathelicidin-regulatory system
Quality and sourcing
LL-37’s complexity makes synthesis quality variable. Lab-tested vendors with explicit mass-spec or HPLC certificates are essential. Improperly synthesised LL-37 may be functionally inactive (in which case the user pays for nothing) or have altered activity profiles.
Populations where LL-37 is contraindicated or high-risk
- Active autoimmune disease (lupus, RA, psoriasis, MS, others) — strong relative contraindication
- Pregnancy and breastfeeding — no safety data
- Active malignancy — limited data; immune-activation implications unclear
- Severe MCAS without antihistamine support — caution; pre-loading recommended
- Severe immunocompromise — uncharacterised in this population
- Under 18 — not studied
Measurement and dosing pitfalls
- mg vs mcg confusion — LL-37 doses are in mcg
- Stacking with immunosuppressants without prescriber input — theoretically antagonistic
- Skipping Herxheimer monitoring — significant reactions warrant pausing
- Treating LL-37 as a routine biohacker compound — the audience and use case are specific to chronic infection
What the community gets wrong
- “Cure for chronic Lyme.” No controlled trials support a cure claim; the in-vitro Borrelia activity is real but doesn’t establish clinical outcomes.
- “General immune booster for healthy users.” The mechanism doesn’t target healthy users productively; immune activation in someone without infection has unclear value.
- “No side effects because it’s natural.” It’s a copy of an endogenous peptide, but supraphysiological doses produce real effects, including Herxheimer reactions and potential autoimmune activation.
FDA / regulatory status
| Jurisdiction | Status | Last verified |
|---|---|---|
| US (FDA) | Not approved for any indication. Sold as a research chemical labelled “not for human consumption.” | 2026-04-29 |
| UK (MHRA) | Not approved as a medicine. Sold as a research chemical. | 2026-04-29 |
| EU (EMA) | Not approved. | 2026-04-29 |
| WADA (sport) | Not specifically prohibited as of the 2026 list, but athletes should consult their governing body. | 2026-04-29 |
Narrative. LL-37 has the same regulatory grey-area status as most peptides in this encyclopedia — research-chemical-only, no licensed pathway anywhere. The compound’s specific use case (chronic infection, particularly chronic Lyme) means that users typically obtain it through chronic-illness clinics that operate on the edge of conventional medicine, with practitioner-supervised protocols rather than self-directed biohacker use.
What to track in Peptrax
LL-37 is not a “general health” compound — almost every user running it is targeting a specific chronic-infection profile, typically chronic Lyme, mycoplasma, persistent fungal infection, or similar. The protocol context (what’s being treated, what else is running, what conventional treatment came before) shapes both the dosing and the expected response pattern. Without that context logged, the dose record is too thin to interpret later.
For most users, the highest-signal log is Herxheimer reaction tracking in the first 4 weeks (severity, duration, specific symptoms) and chronic-infection symptom tracking over 8–12 weeks (the timeline on which improvements, if any, accumulate). Daily subjective ratings of fatigue, brain fog, joint pain, GI symptoms — whichever symptoms the chronic infection drives — are the practical outcome measure.
For sensitive-systems users, the priority log is autoimmune disease activity (flare frequency, symptom intensity) and MCAS reactivity (mast-cell-pattern symptoms, antihistamine use). LL-37 has bidirectional risk in this population — addressing infection components may improve overall picture, while immune activation may worsen autoimmune or mast-cell components.
Across all users, logging concurrent treatments matters — antibiotics, antifungals, herbal protocols, KPV, BPC-157. Chronic-infection protocols are typically multi-component; reconstructing what worked when requires the full picture, not just the LL-37 dose. Practitioner supervision is the standard for this compound and the app’s job is to hold the timeline that makes the practitioner conversation precise.
For personal tracking and informational purposes only — not medical advice.
Sources
- The Potential of Human Peptide LL-37 as an Antimicrobial and Anti-Biofilm Agent — PMC, 2021
- Cathelicidin antimicrobial peptide — Wikipedia
- The structure of the antimicrobial human cathelicidin LL-37 shows oligomerization and channel formation in the presence of membrane mimics — Scientific Reports, 2020
- Efficacy of antimicrobial peptide LL-37 against biofilm forming Staphylococcus aureus strains — ScienceDirect
- Decoding LL-37: Structure and antimicrobial mechanisms against microbial threats — ScienceDirect
- The Human Cathelicidin Antimicrobial Peptide LL-37 as a Potential Treatment for Polymicrobial Infected Wounds — Frontiers in Immunology
- LL-37 Peptide Lyme Disease Insights — Cathelicidin Therapy for Biofilm Disruption (clinical practitioner overview)