Head to head

LL-37 vs Thymosin Alpha-1

Immune

Two compounds that are more often stacked than compared — the side-by-side data, and what actually separates them.

Verdict

Usually stacked — and Thymosin Alpha-1 rests on firmer evidence

LL-37 and Thymosin Alpha-1 appear in each other's stacks in this dataset, so the most common real-world use is together rather than instead of. If you are picking one, the evidence is the honest tiebreak: Thymosin Alpha-1 has approval from a regulator somewhere, though not a current FDA or EMA label, while LL-37 has some human data, but it is small, old, or uncontrolled. That is a difference in how much is known, not a verdict on how well either works.

What you are actually choosing between

Before anything else: the dataset lists LL-37 and Thymosin Alpha-1 in each other's stacks. They are run together more often than they are chosen between, so if you came here for a winner, the first honest answer is that this may not be an either/or.

Both are classed here as immune modulators, so this is a within-class choice: the mechanism is broadly shared and what separates them is kinetics, route, and how much has actually been tested.

The overlap is immune support and inflammation. On this site's goal weighting — an editorial priority score, not a measure of effect size — LL-37 rates 5/5 for immune support and Thymosin Alpha-1 rates 5/5. Outside that overlap only LL-37 goes further, carrying weight for injury repair and skin and hair; Thymosin Alpha-1's declared goals stop at the overlap.

The evidence

This is the part that decides most of it. Thymosin Alpha-1 has approval from a regulator somewhere, though not a current FDA or EMA label — labeled outside the US for hepatitis B and C; not FDA approved. LL-37 has some human data, but it is small, old, or uncontrolled — the human work is small, early, and topical. That gap is the headline, and it is a statement about the literature rather than a promise about you: a compound with trial data can still do nothing for your case, and one without it is unproven rather than disproven.

How they differ in practice

LL-37 is a subcutaneous injection and applied to the skin; Thymosin Alpha-1 is a subcutaneous injection. That is the difference most people actually feel: Thymosin Alpha-1 means reconstituting a vial and injecting; LL-37 does not require either. If needles are the deciding factor, this line settles it before any of the rest matters.

Thymosin Alpha-1 has a characterized half-life of 2 h; LL-37 does not have one published here at all. That asymmetry is worth more than it looks — it usually tracks how much formal pharmacology has been done on a compound.

Committed time differs: LL-37 runs 4 weeks, Thymosin Alpha-1 runs 8 weeks.

Risk and difficulty

The contraindication lists are not the same: LL-37 flags active malignancy, which Thymosin Alpha-1 does not. If any of those describe you they remove a compound from consideration outright, regardless of everything above.

Thymosin Alpha-1 is rated intermediate here and LL-37 advanced. That rating is about how much can go wrong in handling, dosing and monitoring, not about how well either works.

Source notes

What the evidence actually says

Verbatim, so you can check the verdict above against what it was built from.

LL-37

The only human cathelicidin — a 37-residue host-defense peptide cleaved from hCAP-18, with direct antimicrobial and biofilm-disrupting activity plus immunomodulatory and wound-healing signaling roles. The evidence base is overwhelmingly in vitro and animal: bactericidal assays, biofilm models, rodent infection and wound studies. Human work is early — the most substantive is small early-phase testing of topically applied LL-37 on hard-to-heal venous leg ulcers; there is no approved product and no established systemic dosing trial. The 100-500 mcg daily subcutaneous range shown is compounding-pharmacy and community convention only, scaled off the 5 mg vial that is the usual market size, and should be read as low confidence. Human half-life after injection has not been characterized, so it is left null rather than guessed. Note that LL-37 is sequence-identical to an endogenous peptide implicated in psoriasis, rosacea and lupus autoimmunity, which is a genuine reason for caution in anyone with an inflammatory skin or autoimmune condition. Cycles are kept short (about 4 weeks) in practice rather than by evidence.

Thymosin Alpha-1

A 28-amino-acid thymic peptide with genuine clinical use. Marketed as thymalfasin (Zadaxin) and approved in a number of countries outside the US for chronic hepatitis B and C and as a vaccine adjuvant; it is NOT FDA approved. The best-established regimen is the labeled one: 1.6 mg subcutaneously twice weekly, which is where the typical dose here comes from. Higher daily dosing has been studied in sepsis and in hospitalised COVID-19 patients, which is the basis for the upper end of the range; that is an acute inpatient context, not a wellness protocol. Approved hepatitis courses run 24 weeks or longer, so the 8-week cycle shown here reflects common non-clinical use rather than the label. Reported plasma half-life is roughly 2 hours, but its immunological effect outlasts plasma levels.

Side by side

The numbers

LL-37 compared with Thymosin Alpha-1
Attribute	LL-37	Thymosin Alpha-1
Class	Immune	Immune
Routes	Subcutaneous, Topical	Subcutaneous
Dose range	100 mcg–500 mcg (typical 250 mcg)	800 mcg–3.2 mg (typical 1.6 mg)
Frequency	Once daily	Twice a week
Half-life	Not characterized	2 h
Cycle length	4 weeks	8 weeks
Experience	Advanced	Intermediate
Evidence	Limited human data	Approved elsewhere
Contraindications	Pregnant / nursing Under 18 Active malignancy	Pregnant / nursing Under 18
Side effects	Injection site redness, itching, wheal or induration — LL-37 degranulates mast cells, so local histamine-type reactions are the expected complaint Flu-like feeling or transient fatigue after a dose Headache Flushing Theoretical concern with malignancy: LL-37 is pro-angiogenic and has been reported to promote proliferation in some tumor models	Injection site discomfort, redness or transient swelling Short-lived flu-like feeling or fatigue after a dose Muscle aches Rare rash

Turn a typical dose into a mark on the syringe: LL-37Thymosin Alpha-1

Goals

Where they overlap, and where they do not

Goal	LL-37	Thymosin Alpha-1
immune support	LL-37: 5/5	Thymosin Alpha-1: 5/5
inflammation	LL-37: 4/5	Thymosin Alpha-1: 3/5
injury repairone only	LL-37: 3/5	Thymosin Alpha-1: —
skin and hairone only	LL-37: 3/5	Thymosin Alpha-1: —
gut healthone only	LL-37: 2/5	Thymosin Alpha-1: —
longevityone only	LL-37: —	Thymosin Alpha-1: 2/5
recovery and sleepone only	LL-37: —	Thymosin Alpha-1: 2/5

They overlap on 2 goals and diverge on 5. Weights are this site’s editorial priority score out of 5 — how central a goal is to why people use a compound. They are not effect sizes and two 5s do not mean two equal results.

Go deeper

MonographLL-37Mechanism, protocol, storage, sources.MonographThymosin Alpha-1Mechanism, protocol, storage, sources.ToolReconstitution calculatorTurn either dose above into a mark on the syringe.

Educational information only, not medical advice. Talk to a licensed clinician before starting, changing, or stopping anything.