Best Peptides for Immune Support
Immune modulation claims, including the compound approved in dozens of countries.
How this is graded
Every compound below carries a REGEN research grade, from S (regulatory approval behind the use it is bought for) down to F (no clinical evidence). Ordering follows that grade rather than search volume, so the compound at the top is the one with the most evidence, not the one most often sold. Doses are those reported in published protocols and are not recommendations.
1. Thymosin Alpha-1
Thymosin Alpha-1 is a naturally occurring 28-amino-acid peptide fragment of prothymosin alpha, produced by the thymus gland and involved in T-cell maturation and innate immune signaling (notably through TLR9). Under the brand name Zadaxin, it's an approved drug in more than 35 countries — including Italy and China — for chronic hepatitis B and C and as a general immune-modulating agent. It has never been FDA-approved in the United States; as of a February 2026 reclassification, it holds FDA 503A Category 2 status, meaning US patients can access it only by prescription through licensed compounding pharmacies.
2. LL-37
LL-37 is the human cathelicidin antimicrobial peptide, a 37-residue C-terminal fragment of the hCAP18 precursor protein, named for its first two residues (leucine-leucine) and total length. It's a cationic, amphipathic, alpha-helical peptide that disrupts bacterial cell membranes for broad-spectrum antimicrobial activity, and plays a role in the body's innate immune response at sites of infection and inflammation. It's also studied for wound healing and angiogenesis. No established human clinical dosing protocol exists — nearly all substantive data is preclinical or in-vitro, and it's sold only as a research compound.
3. KPV
KPV (Lysine-Proline-Valine) is a synthetic tripeptide corresponding to the C-terminal fragment of alpha-melanocyte-stimulating hormone (α-MSH), residues 11-13. It retains α-MSH's anti-inflammatory melanocortin signaling but, being only three amino acids, lacks the pigmentation-darkening and sexual-arousal effects seen with full-length analogs like Melanotan II. Research interest centers on gut inflammation, skin inflammation, and wound healing via modulation of the NF-κB pathway. It's sold only as a research compound — no clinical trial or FDA approval data exists.
4. VIP (Vasoactive Intestinal Peptide)
VIP (Vasoactive Intestinal Peptide) is a 28-amino-acid neuropeptide that acts as a vasodilator, bronchodilator, and smooth-muscle relaxant, with additional anti-inflammatory and immunomodulatory properties mediated through the VPAC1/VPAC2 receptors. It disappears from plasma extremely quickly after IV administration — a first-order half-time of about one minute — which is why intranasal and subcutaneous research routes are used to achieve more sustained local exposure. It's sold only as a research compound; no FDA approval exists for VIP itself.
5. Glutathione
Glutathione is a tripeptide (glutamate-cysteine-glycine) produced naturally in the liver and considered the body's primary intracellular antioxidant, neutralizing free radicals and supporting detoxification pathways. Though technically a tripeptide, it's marketed and used almost exclusively as a wellness supplement rather than a research peptide — sold as an oral/liposomal capsule and as an IV or intramuscular injectable at wellness clinics, often alongside NAD+ on the same infusion menu. It's regulated as a dietary/food ingredient rather than an approved drug, and injectable glutathione marketed specifically for skin lightening has drawn FDA scrutiny.
At a glance
| Compound | Grade | Reported dose | Half-life |
|---|---|---|---|
| Thymosin Alpha-1 | Agrade | 1.6 mg · 2x weekly | ~2 hours |
| LL-37 | Dgrade | No standardized dose · no established human protocol | No formal human pharmacokinetic data published |
| KPV | Dgrade | 200–500 mcg · 1x daily | Likely minutes (unmodified tripeptide) — no formal human pharmacokinetic data exists |
| VIP (Vasoactive Intestinal Peptide) | Cgrade | 50–300 mcg · 1–2x daily | ~1 minute (IV plasma disappearance half-time) |
| Glutathione | Dgrade | 200–1000 mg · route-dependent | Very short in circulation (minutes) — rapidly recycled intracellularly via the glutathione redox cycle rather than persisting as free plasma glutathione |
Frequently asked questions
Which peptide has the most evidence for immune support?
Thymosin Alpha-1, at research grade A. REGEN Research Tier A — human RCTs, plus approval in roughly 35 countries as Zadaxin — but not by the FDA, and not for general immune support.
How many compounds are compared here?
5: Thymosin Alpha-1, LL-37, KPV, VIP (Vasoactive Intestinal Peptide), Glutathione.
What doses are reported for Thymosin Alpha-1?
Published protocols report 1.6 mg, 2x weekly. This is what the literature describes, not a recommendation.
References
- Thymosin-α1 for people with chronic hepatitis B (Cochrane Review CD014610) · Htet NH, et al. · 2022
- Molecular Dynamics Simulations of Human Antimicrobial Peptide LL-37
- Immunomodulatory Functions of the Human Cathelicidin LL-37-Derived Peptides
- Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial · Grönberg A, Mahlapuu M, Ståhle M · 2014
- PepT1-mediated tripeptide KPV uptake reduces intestinal inflammation · Dalmasso G, et al. · 2008
- Vasoactive intestinal peptide in man: pharmacokinetics, metabolic and circulatory effects