LL-37 vs Thymulin (FTS)
Human cathelicidin-derived antimicrobial peptide (37 amino acids) that disrupts bacterial membranes at MIC 0.62 μM against S. aureus, neutralizes endotoxin (LPS) to prevent septic shock, and has reached Phase II clinical trials as Ropocamptide for wound healing — achieving 6-fold accelerated healing at 0.5 mg/mL in venous leg ulcers
Zinc-dependent thymic hormone for immune restoration and T cell maturation
Written by Michael Carroll — Owner, Director of Research · Reviewed by the Peptide Initiative Research Team · Editorial standards
Quick comparison
Dose range
LL-37
1.6–1.6 mg/mL
Thymulin (FTS)
1–2 mg
Frequency
LL-37
Once daily
Thymulin (FTS)
Once daily
Administration
LL-37
Topical application (wound healing)
Thymulin (FTS)
Subcutaneous injection
Cycle length
LL-37
12+ weeks
Thymulin (FTS)
4-6 weeks
Onset speed
LL-37
Moderate (1-2 weeks)
Thymulin (FTS)
Moderate (1-2 weeks)
Evidence level
LL-37
Moderate human trials (Phase 1-2)
Thymulin (FTS)
Limited human trials
Benefit ratings
Wound Healing
Fighting Infections
Immune Boost
Immune Restoration
Anti-Inflammatory
Age-Related Immune Decline
Compound specifications
LL-37
Molecular formula
C205H340N60O53
Molecular weight
4,493.26 Da
Half-life
Short systemic half-life (minutes) due to protease susceptibility; local tissue persistence at wound sites is longer due to binding to extracellular matrix components and lipid membranes
Bioavailability
Topical application achieves high local wound-bed concentrations; systemic bioavailability limited by rapid proteolytic degradation and serum protein binding; not intended for oral delivery
CAS number
154947-66-7
Thymulin (FTS)
Molecular formula
C33H54N12O15
Molecular weight
858.9 g/mol
Half-life
Approximately 2 hours
Bioavailability
Low oral bioavailability (injected administration required)
CAS number
63958-90-7
Dosing compared
LL-37
Topical
0.5 mg/mL gel
Twice weekly · 4 weeks
Lowest dose in the LL-37 (ropocamptide) Phase I/IIa venous leg-ulcer trial and the most effective: ~6-fold faster healing and ~68% ulcer-area reduction vs placebo, applied to the wound twice weekly [4].
1.6 mg/mL gel
Twice weekly · 4 weeks
Mid dose in the same trial; ~3-fold improvement and ~50% area reduction vs placebo. The highest tested concentration (3.2 mg/mL) showed no benefit over placebo, so dose escalation above this is not supported [4].
Thymulin (FTS)
Subcutaneous injection
1-2 mg
Once daily (often dosed in the evening) · 10-20 day courses, repeated cyclically
Research-practice dosing for immune support; thymulin requires injectable delivery due to low oral bioavailability and a zinc ion for activity, so zinc co-supplementation is commonly paired [1].
Intradermal injection
100-400 mcg
Three times weekly · Several weeks
Lower microgram-range intradermal dosing is used in some research protocols as a conservative entry point [1].
Best suited for
LL-37
Treatment of chronic non-healing wounds including venous leg ulcers and diabetic ulcers
LL-37 is particularly well-suited for individuals focused on treatment of chronic non-healing wounds including venous leg ulcers and diabetic ulcers. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Immune defense against antibiotic-resistant bacterial infections (MRSA, Pseudomonas)
LL-37 is particularly well-suited for individuals focused on immune defense against antibiotic-resistant bacterial infections (mrsa, pseudomonas). Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Anti-biofilm strategies for chronic wound infections and medical device-associated infections
LL-37 is particularly well-suited for individuals focused on anti-biofilm strategies for chronic wound infections and medical device-associated infections. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Boosting innate immune defense in immunocompromised or aging individuals
LL-37 is particularly well-suited for individuals focused on boosting innate immune defense in immunocompromised or aging individuals. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Thymulin (FTS)
Age-Related Immune Decline
Thymulin levels naturally drop significantly in elderly populations. [9][10] Supplementation can restore T cell maturation and immune responsiveness in aging. [23] Research shows thymulin can reverse age-related thymic involution and restore helper/suppressor T cell balance. [7][11]
Recovery from Severe Malnutrition
In severely malnourished individuals, the thymus shrinks and T cell development is impaired. [24] In vitro studies show thymulin can restore T cell maturation even in those with thymic involution, [13] making it useful in recovery protocols.
Chronic Inflammatory Conditions
Thymulin inhibits NF-κB activation and suppresses pro-inflammatory cytokines (IL-6, TNF-α, IL-8). [14][16] Animal models show effectiveness in lung diseases, inflammatory pain, and neuroinflammation. [14][15][17] Anti-inflammatory effects work through p38 MAPK suppression. [15]
Side effects
LL-37
Common
- Local site irritation
- Transient stinging or burning
- Mild perilesional erythema
- Increased wound exudate
Uncommon
- Allergic contact reaction
Serious
- Hemolytic activity at systemic concentrations
Thymulin (FTS)
Common
- Local injection site reactions
- Mild fatigue or lethargy
- Transient headache
Uncommon
- Mild fever or chills
- Sleep disturbance or vivid dreams
- Appetite changes
- Transient lymph node swelling
Serious
- Severe allergic reaction
- Uncontrolled immune activation
Safety & evidence
LL-37
Evidence level
Moderate human trials (Phase 1-2)
FDA status
Research compound
Safety overview
LL-37 is an endogenous cathelicidin antimicrobial peptide naturally produced by immune cells and epithelial tissues, conferring inherent biocompatibility and low toxicity at physiological concentrations. Synthetic LL-37 shows excellent safety in in vitro immune assays and animal models with no hepatotoxicity, nephrotoxicity, or genotoxicity at relevant doses. At elevated concentrations, the cationic amphipathic structure can cause hemolysis and cell membrane damage, but therapeutic doses are far below these thresholds. Injection site reactions are minimal in research applications.
Contraindications
- Known hypersensitivity to cathelicidin peptides or formulation components
- Active hemolytic conditions — LL-37 demonstrates concentration-dependent hemolytic activity
- Pregnancy and breastfeeding — insufficient reproductive safety data from clinical trials
- Severe renal impairment — peptide clearance may be altered
Thymulin (FTS)
Evidence level
Limited human trials
FDA status
Research compound
Safety overview
Thymulin is a naturally occurring thymic hormone with favorable safety profile in research. No reported serious adverse events in animal models even at high doses. [8][14] Limited human safety data but observed studies suggest good tolerability. Requires concurrent zinc supplementation for biological activity [6][7] and additional safety assurance. Most concerns relate to immune overactivation in susceptible individuals, not direct peptide toxicity.
Contraindications
- Uncontrolled autoimmune disease
- Severe zinc deficiency requiring IV repletion
- Thymic tumors or malignancies
- Pregnancy (limited safety data)
Which is right for you?
Choose LL-37 if...
- Treatment of chronic non-healing wounds including venous leg ulcers and diabetic ulcers
- Immune defense against antibiotic-resistant bacterial infections (MRSA, Pseudomonas)
- Anti-biofilm strategies for chronic wound infections and medical device-associated infections
- Boosting innate immune defense in immunocompromised or aging individuals
Choose Thymulin (FTS) if...
- Immune system restoration
- T cell maturation in immunocompromised states
- Age-related immune decline
- Chronic inflammatory conditions