Immune & defense Thymic immune peptide
Thymulin
Regulatory status
Status at a glance
503A compounding status
Not nominated
We found no pending nomination for the 503A bulks list. Unless the substance has another legal pathway (for example, a USP monograph or use in an FDA-approved drug), 503A pharmacies generally may not compound with it.
- FDA approval
- Not FDA-approved for any use
- 503B outsourcing
- Not determined
- Anti-doping (WADA)
- Not on the WADA Prohibited List
- DEA schedule
- Not a controlled substance
About peptide status
Most peptides discussed here are not FDA-approved for any use, and products labeled “research use only” are not for human use. Removal from Category 2 does not authorize compounding. PCAC votes are non-binding recommendations; FDA and HHS make the final decisions.
This is not medical or legal advice, and we do not publish dosing, sourcing or reconstitution information. Talk with a licensed clinician before using any peptide.
If you think you are having a medical emergency, call 911.
Key takeaway
Thymulin is a zinc-dependent thymic peptide involved in immune-cell development, sold on the "research peptide" market for immune support. Its biology is well described, but there is essentially no interventional human evidence for the administered peptide. As of 2026 it is not FDA-approved.
At a glance
- FDA status
- Not FDA-approved, sold in the wellness/gray market
- What it is
- Thymic immune hormone, biologically active only when bound to zinc
- Research
- Endogenous biology well studied, but no modern trials of giving it as a therapy
- Global approval
- Not approved anywhere as a treatment
- Evidence strength
- Low research
Summary
Thymulin is a zinc-dependent thymic peptide tied to immune-cell development. See how it works, what the research shows, and where it stands with the FDA.
What is thymulin?
Thymulin is a nine-amino acid peptide produced by the thymus gland, where immune cells mature. It is unusual in that it is only biologically active when coupled to zinc. It has historically been studied as a thymic immune hormone, and it is sold through wellness and "research peptide" channels for immune support. It is not an approved medicine.
How does it work?
Thymulin is involved in the development and differentiation of T-cells, the immune system's coordinating cells, and has been reported in animal work to have anti-inflammatory and pain-modulating effects. A notable feature of its biology is the zinc link: zinc deficiency lowers active thymulin levels and shifts the immune response. These mechanisms come largely from animal and physiological studies. This describes the proposed mechanism, separate from demonstrated benefit from giving the peptide.
Is it FDA-approved?
Safety note
Status: Not FDA-approved, sold in the wellness/gray market
Category: Wellness and performance · Primary body area: Immune & defense
No. Thymulin is not approved by the FDA or any regulator as a therapy. It is not on FDA compounding lists and was not among the peptides reviewed at the 2026 FDA compounding advisory meetings.
What does the research show?
Editor’s note
Evidence strength: Low research
The endogenous biology is well described, but there is essentially no interventional human efficacy evidence for the administered peptide.
The evidence is largely preclinical and physiological. According to PubMed, the main human-relevant observations are that thymulin activity tracks zinc status and thymic function, summarized in reviews of its biology and of zinc and immunity. There are no modern controlled trials of administered thymulin for any wellness or immune use, so its marketed benefit is unestablished.
Sources: a review of thymulin biology (Reggiani et al., Annals of the New York Academy of Sciences, 2009, DOI: 10.1111/j.1749-6632.2008.03964.x) and a review of zinc, thymulin, and immunity (Prasad, Journal of Nutrition, 2007, DOI: 10.1093/jn/137.5.1345), indexed on PubMed. This document is educational, is not medical advice or a health claim, and is not an offer to sell any product.
Registered human trials
0 registered human trials on ClinicalTrials.gov that we reviewed
Sources
- [1]
- [2]
Compare every peptide’s status in the peptide regulatory status database
More for Immune & defense
View all immune & defense peptides →- In clinical trials Immune & defense
Aviptadil
Aviptadil is a synthetic form of vasoactive intestinal peptide (VIP), a signaling molecule that acts on lung receptors, and it has been studied mainly for severe COVID-19 respiratory failure. In the NIH-funded TESICO trial of 461 patients, aviptadil did not beat placebo on the 90-day recovery scale (odds ratio 1.11, 95% CI 0.80 to 1.55, p = 0.54). Ninety-day mortality was 38% with aviptadil versus 36% with placebo (p = 0.78), and the trial stopped early for futility. As of 2026 it is not FDA-approved for any use.
- FDA-approved Immune & defense
Cyclosporine
Cyclosporine (also spelled ciclosporin; brands include Sandimmune, Neoral, and the eye drop Restasis) is a cyclic peptide from a fungus that suppresses the immune system, and it transformed organ transplantation when it arrived in the 1980s. It works by blocking the activation of T cells. It has been FDA-approved in the U.S. since 1983, is available in oral, intravenous, and eye-drop forms, and carries boxed warnings for the systemic versions.
- FDA-approved Immune & defense
Enfuvirtide
Enfuvirtide (formerly sold as Fuzeon) is a peptide HIV drug that blocks the virus from entering CD4 immune cells, the first of the so-called fusion inhibitors. It was used in treatment-experienced patients whose virus is no longer controlled by other antiretrovirals. It was FDA-approved in the U.S. in 2003, but Fuzeon was discontinued there in February 2025.
- Not FDA-approved Immune & defense
Ll-37
LL-37 is the body's natural antimicrobial "host-defense" peptide, intensely studied as part of the immune system and sold on the "research peptide" market for antimicrobial and immune support. Its biology is well described, but there is no approved product and no human efficacy evidence for the injected wellness use, and its effects are context-dependent. As of 2026 it is not FDA-approved.
- In clinical trials Immune & defense
Murepavadin
Murepavadin is an investigational antimicrobial peptidomimetic that targets a protein unique to Pseudomonas aeruginosa, developed by Polyphor for serious lung infections. Its intravenous Phase 3 program was halted after an unexpected rate of kidney injury, and later inhaled development did not mature. As of 2026 it is not approved.
- In clinical trials Immune & defense
Nangibotide
Nangibotide is an investigational peptide that inhibits the inflammatory receptor TREM-1, developed by Inotrem as an intravenous treatment for septic shock. Its Phase 2b trial did not meet its primary endpoint, though a signal appeared in a subgroup of patients with high levels of a related biomarker. As of 2026 it is not approved.