Summary
Thymulin is a nine amino acid hormone made by the thymus, the gland where immune T cells mature, that requires zinc to be biologically active and helps T cells mature. Its clinical record is thin and old: two small double blind trials (neither patients nor doctors knew who got the drug) published in 1987 found a synthetic form (nonathymulin) at 5 mg daily improved rheumatoid arthritis in 56% of patients versus 17% on placebo, but development stopped and no modern trial exists, while more recent rodent work shows analgesic (pain relieving) and anti-inflammatory effects. It is not approved anywhere, has never been nominated for FDA's compounding lists, and falls under WADA's S0 prohibition on unapproved substances.
What is Thymulin?
Thymulin is a zinc dependent nonapeptide (9 amino acids) hormone produced by thymic epithelial cells. It is also known as Facteur thymique serique (FTS), Serum thymic factor, FTS-Zn, Nonathymulin, Thymic nonapeptide, pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn.
How does it work?
Thymulin binds zinc in a one to one complex, and only the zinc bound form is active. It promotes differentiation of T cell precursors, modulates T cell subsets and natural killer activity, and is regulated by pituitary hormones such as growth hormone and prolactin, so it is considered part of a thymus to neuroendocrine axis. Rodent studies show it reduces pro-inflammatory cytokines and pain behaviors, possibly through effects on glial and immune cells.
| Cluster | Immune and antimicrobial |
|---|---|
| Routes | Injection (1987 trials); Subcutaneous injection and intranasal (as sold, not from published trials) |
| Conditions studied | Inflammation and inflammatory bowel disease; Peripheral and small fiber neuropathy; Immune support and immune deficiency; Autoimmune disease; Chronic pain |
| Record | v2, draft, verified Sep 22, 2026 |
What does the evidence say about Thymulin?
Human evidence comes from two double blind placebo controlled trials in rheumatoid arthritis reported together in 1987 (Amor et al.), which compared nonathymulin 1, 5, and 10 mg daily and found the 5 mg dose produced clinical improvement by global assessment in 56% of patients versus 17% on placebo with minimal adverse effects. The work was not replicated and no trial has been published since. Preclinical work by Dardenne, Bach, and later groups characterized the zinc dependence and, in rodents, anti-inflammatory and analgesic effects of thymulin and a synthetic analog. PeptideAgent grades the evidence human RCT on the strength of the 1987 trials but notes they are small, old, and unconfirmed.
| Evidence type | Indexed studies | Participants (human) |
|---|---|---|
| Human randomized trials | 1 | n/a |
| Human observational studies | 0 | n/a |
| Animal studies | 3 | n/a |
| All indexed studies | 4 | n/a |
Human evidence
Amor 1987: two randomized double blind placebo controlled trials in rheumatoid arthritis compared nonathymulin at 1, 5, and 10 mg per day; the 5 mg dose gave significant clinical improvement (56% of all entered patients improved by global assessment versus 17% on placebo, p below 0.02) and improvement in four objective measures, with minimal side effects and no clear change in immune parameters. No subsequent controlled trial of thymulin in any condition has been indexed. Circulating thymulin levels have been measured as a marker of thymic function in aging, zinc deficiency, and malnutrition, which is observational, not therapeutic, evidence.
Animal evidence
Dardenne 1982 (PNAS) showed that zinc and certain other metals are required for the biological activity of serum thymic factor, defining thymulin as a metallopeptide. Reggiani 2014 reviews rodent studies in which thymulin or its analog reduced inflammation and pain and in which thymulin gene therapy corrected hormonal abnormalities in athymic (nude) mice. Safieh-Garabedian 2019 reviews rodent neuropathic pain models in which a thymulin related peptide reduced hyperalgesia and inflammatory mediators.
Key studies
| Study | Design and population | Outcome | Grade |
|---|---|---|---|
| Nonathymulin in rheumatoid arthritis: two double blind, placebo controlled trials1987 PMID 3310925 | Two randomized, double blind, placebo controlled trials comparing 1, 5, and 10 mg per dayAdults with rheumatoid arthritis | 5 mg per day improved 56% of patients by global assessment versus 17% on placebo (p below 0.02), with minimal adverse effects | Evidence: Human RCT evidence |
| Contribution of zinc and other metals to the biological activity of the serum thymic factor1982 PMID 6957870 | In vitro and in vivo biochemical studyPurified serum thymic factor and rodent T cell assays | Zinc binding is required for biological activity, defining thymulin as a metallopeptide | Evidence: Animal-only evidence |
| Physiology and therapeutic potential of the thymic peptide thymulin2014 PMID 24588820 | Narrative reviewRodent and human physiology studies, thymulin gene therapy in athymic mice | Summarizes neuroendocrine regulation, anti-inflammatory and analgesic effects in rodents, and gene therapy results in nude mice | Evidence: Animal-only evidence |
| Targeting inflammatory components in neuropathic pain: The analgesic effect of thymulin related peptide2019 PMID 30503917 | Review of rodent neuropathic pain studiesRodent models of inflammatory and neuropathic pain | A thymulin related peptide reduced hyperalgesia and inflammatory mediators in rodents | Evidence: Animal-only evidence |
Conditions studied
| Condition | Grade | Note |
|---|---|---|
| Inflammation and inflammatory bowel disease | Not graded | KPV, thymosin alpha-1, LL-37, VIP, and BPC-157 are marketed as anti-inflammatory peptides. Thymosin alpha-1 has human trials in hepatitis and sepsis outside the United States. KPV has rodent colitis data only. VIP analogs have been studied in small human trials for sarcoidosis and pulmonary hypertension. |
| Peripheral and small fiber neuropathy | Evidence: Animal-only evidence | A thymulin related peptide reduced pain hypersensitivity in rodent models; no human neuropathy study. |
| Immune support and immune deficiency | Evidence: Animal-only evidence | Zinc dependent thymic hormone studied mainly in rodents for immune effects; no human immune function study. |
| Autoimmune disease | Evidence: Human RCT evidence | Two placebo controlled trials in rheumatoid arthritis found global improvement in 56% versus 17% on placebo; never developed further and not approved anywhere. |
| Chronic pain | Evidence: Animal-only evidence | A thymulin related peptide reduced inflammatory and neuropathic pain in rodents; no human pain study. |
Is Thymulin legal in the United States?
FDA and compounding status
Not FDA approved and not approved in any country. Thymulin does not appear on the FDA 503A bulks list, in Category 2, or among the withdrawn nominations as of the FDA pages current to April 2026, and it has no USP monograph, so there is no lawful basis for a US compounding pharmacy to dispense it. It was not part of the July 2026 advisory committee review. Products sold online are research chemicals.
WADA status
WADA prohibited. Athletes subject to anti-doping testing should treat this as prohibited at all times unless the current prohibited list says otherwise.
Regulatory timeline
No regulatory events recorded.
What published studies of Thymulin used
Ranges below are reported from published studies and labeling only. PeptideAgent does not recommend doses or protocols.
Rheumatoid arthritis trials (Amor 1987): nonathymulin 1, 5, or 10 mg per day, with 5 mg identified as most effective. No dosing has been established for any other use, and no modern human dose finding study exists.
Routes reported
| # | Route |
|---|---|
| 1 | Injection (1987 trials) |
| 2 | Subcutaneous injection and intranasal (as sold, not from published trials) |
What are the side effects and interactions of Thymulin?
Side effects
| # | Reported side effect |
|---|---|
| 1 | Minimal adverse effects reported in the 1987 rheumatoid arthritis trials |
| 2 | No modern human safety data |
| 3 | Injection site reactions reported anecdotally |
| 4 | Immunogenicity risk from impurities in unregulated products |
Interactions
| # | Interaction |
|---|---|
| 1 | No human interaction data exist |
| 2 | Zinc status affects activity, so zinc supplements or deficiency could change effect (mechanistic, not clinical, evidence) |
| 3 | Immunosuppressants: theoretical opposition of effect |
Contraindications
| # | Contraindication |
|---|---|
| 1 | Pregnancy and breastfeeding (no data) |
| 2 | Autoimmune disease outside the studied rheumatoid arthritis setting (no data) |
| 3 | Athletes subject to WADA testing (prohibited at all times under S0) |
| 4 | Any use requiring an approved product: none exists |
How do people access Thymulin legally?
Typical cost: Not available through licensed channels. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity.
Verified access options
Step 1
No lawful United States access path identified on the last verified date.
Step 2
Not available as an FDA approved product, not nominated for the 503A bulks list, and not eligible for compounding under section 503A or 503B.
Step 3
Products labeled research use only are not lawful for human use and are not verified for identity or purity.
Access paths are verified against public regulatory records and prescriber licensing. We never list unlicensed vendors.
Compare Thymulin
What's actually offered, and what that means for you
Licensed compounding pharmacies, clinics, and telehealth prescribers openly offer many unapproved peptides, and prescribers write prescriptions for them. That does not make thymulin lawful. Thymulin is not FDA approved and not on the 503A bulks list, so a pharmacy has no lawful basis to compound it. [6] [7]
Enforcement is uneven. FDA mostly acts through warning letters to compounders and online sellers, Category 2 safety listings, and import alerts that let it detain shipments, rather than stopping every pharmacy. State pharmacy boards oversee pharmacies day to day, and their rules differ. [7] [9] [10] [11] [12]
What changes for you
- No FDA review of the product: FDA does not check a compounded drug's safety, effectiveness, or quality before it is sold. [12]
- Identity, purity, sterility, and dose accuracy can vary from batch to batch. [7]
- Insurance rarely covers it, so you usually pay cash.
- For tested athletes, thymulin is prohibited at all times on the WADA list, whatever the source. [8]
What to check
These checks lower some risks, but they do not make an unlawfully compounded product lawful or safe. Check for:
- A 503A pharmacy licensed in your state (your state board of pharmacy publishes license lookups). [12]
- A real evaluation by a licensed prescriber, not just an online form.
- A certificate of analysis for the specific batch.
Frequently asked questions
Is thymulin legal in the United States?
It is not FDA approved, has never been nominated for the 503A bulks list (FDA's list of raw ingredients pharmacies may use to compound drugs for individual patients), and has no USP monograph (an official drug quality standard), so no pharmacy can lawfully compound it. It has not been through FDA's Category 2 review (FDA's safety screen of nominated compounding ingredients) because nobody has nominated it. Possession is not a crime, but research chemical products are not for human use. [6] [7]
Does thymulin work for inflammation or autoimmune disease?
The only human evidence is two small double blind trials in rheumatoid arthritis published in 1987, in which 5 mg daily of synthetic thymulin (nonathymulin) improved 56% of patients versus 17% on placebo. That result was never replicated and development stopped. Rodent studies since then show reduced inflammation and pain, but nothing has been tested in modern human trials. [1] [4]
What are the side effects of thymulin?
Largely unknown. The 1987 rheumatoid arthritis trials reported minimal adverse effects, and there are no modern human safety data. Injection site reactions are reported anecdotally. Because products are unregulated, impurity and immunogenicity risk is a practical concern. [1]
How is thymulin taken?
The 1987 trials used 1, 5, or 10 mg of nonathymulin per day by injection, with 5 mg the most effective. Products sold online are subcutaneous or intranasal preparations with no published human dose. Activity depends on zinc binding, which is another reason unregulated products are unpredictable. [1] [2]
How much does thymulin cost?
There is no licensed price. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity. [6]
Is thymulin banned by WADA?
It is not named, but section S0 of the WADA Prohibited List prohibits at all times any pharmacological substance with no current approval by a governmental health authority for human use. Thymulin has no approval anywhere, so it falls under S0. [8]
Thymulin vs thymosin alpha-1: what is the difference?
Both are thymus derived immune peptides, but their evidence differs sharply. Thymosin alpha-1 (28 amino acids) has decades of randomized trials in hepatitis B and sepsis and is approved in more than 30 countries. Thymulin (9 amino acids, zinc dependent) has two 1987 rheumatoid arthritis trials and rodent data, with no approval anywhere. Thymulin is also distinct from thymalin, a crude thymus extract used in Russia. [1] [4]
Why does thymulin need zinc?
The peptide is inactive on its own. A 1982 study showed that zinc, and to a lesser extent a few other metals, must bind the peptide for it to have biological activity on T cells, which is why it is sometimes sold as FTS-Zn. Low thymulin activity in zinc deficiency and malnutrition is one of the ways this was discovered. [2] [3]
Decisions about starting, stopping, or combining any treatment belong with a licensed clinician who knows your history.
Sources
Numbered citations above point to these primary sources. PubMed entries link to the indexed abstract.
- [1]Amor B et al. Nonathymulin in rheumatoid arthritis: two double blind, placebo controlled trials. Ann Rheum Dis 1987PubMed 3310925, 1987
- [2]Dardenne M et al. Contribution of zinc and other metals to the biological activity of the serum thymic factor. Proc Natl Acad Sci USA 1982PubMed 6957870, 1982
- [3]Bach JF, Dardenne M. Thymulin, a zinc-dependent hormone. Med Oncol Tumor Pharmacother 1989PubMed 2657247, 1989
- [4]Reggiani PC et al. Physiology and therapeutic potential of the thymic peptide thymulin. Curr Pharm Des 2014PubMed 24588820, 2014
- [5]Safieh-Garabedian B et al. Targeting inflammatory components in neuropathic pain: the analgesic effect of thymulin related peptide. Neurosci Lett 2019PubMed 30503917, 2019
- [6]FDA: Bulk drug substances used in compounding under section 503A of the FD&C ActFDA, 2026
- [7]FDA: Certain bulk drug substances for use in compounding may present significant safety risks (Category 2 list, content current as of April 22, 2026)FDA, 2026
- [8]WADA Prohibited List, section S0 non-approved substancesWADA, 2026
- [9]FDA: Compounding inspections, recalls, and other actions (warning letters to compounders)FDA
- [10]FDA warning letters database: July 30, 2019 letter to a 503A pharmacy that compounded BPC-157 acetate outside section 503AFDA, 2019
- [11]FDA Import Alert 66-41: Detention without physical examination of unapproved new drugs promoted in the U.S. (includes peptide entries)FDA
- [12]FDA: Compounding and the FDA, questions and answersFDA
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