What Is Thymulin?

1. What is thymulin, and where was it discovered?

A French team led by Jean-François Bach and Mireille Dardenne purified a “circulating thymic factor” from about 1,000 liters of pig serum and found it was a nine-amino-acid peptide, as reported in Dardenne and colleagues’ 1977 isolation paper. A companion paper by Pléau and colleagues worked out its structure and showed that a lab-made copy behaved like the natural factor.

The zinc story came five years later. When the group stripped metals from the peptide, its activity vanished; adding zinc back restored it, with the best effect at one zinc ion per molecule. The 1982 PNAS study proposed “thymulin” as the name for this zinc-bound, active form.

In blood, thymulin does not all circulate free. Earlier work from the same lab found that part of it rides on a larger carrier protein of roughly albumin’s size. PubChem lists the zinc-free peptide at 858.9 g/mol.

How is it different from other thymus peptides?

Several unrelated products share the “thym-” prefix, and sellers sometimes blur them together. They are distinct molecules:

A study result for any one of these says nothing about the others.

2. How does thymulin work in the body?

Thymulin’s main job is helping T cells develop. A 2009 review by Reggiani and colleagues describes it acting at several steps of T-cell differentiation, both inside the thymus and in the rest of the body. Its discoverers called it a zinc-dependent hormone that boosts several T-cell functions in normal or partly thymus-deficient recipients.

It also trades signals with the endocrine system. According to the Reggiani review:

• Growth hormone raises it. Children born with growth hormone (GH) deficiency had low thymulin that climbed toward normal on GH treatment, and people with acromegaly, a state of GH excess, had higher levels than peers of the same age. In animal and cell work, prolactin and thyroid hormone also stimulated its release.
• It may act on the pituitary, in rats. In rat pituitary cells and tissue, thymulin altered the release of LH, prolactin, ACTH and other hormones. This has not been demonstrated in people.

Thyroid status shows up clearly in human blood levels. Fabris and colleagues found higher thymulin in people with an overactive thyroid and lower thymulin in people with an underactive one, and both shifts reversed once the thyroid problem was treated.

3. What happens to thymulin with age and zinc deficiency?

Age

Consolini and colleagues measured thymulin in 93 healthy people aged from newborn to 80. The pattern below roughly follows the gradual shrinking of the thymus over life.

Zinc

Because the hormone needs zinc to work, measured thymulin activity is a sensitive readout of zinc shortage. The human studies here raised people’s own thymulin by correcting zinc. None of them gave thymulin itself.

The practical point: in these studies, low thymulin was fixed by addressing zinc, not by injecting a peptide. The 200 mg/day zinc sulfate figure is a trial dose in Crohn’s disease and should not be read as a general supplement recommendation.

4. What do human trials of thymulin show?

Rheumatoid arthritis

The most encouraging human result comes from two randomized, double-blind, placebo-controlled trials comparing nonathymulin at 1, 5 and 10 mg/day, published by Amor and colleagues in 1987.

The 5 mg dose did best of the three, yet the drug produced no clear shift in the immune markers the researchers measured. The trials were small and run by the peptide’s developers, and we found no later study that repeated the result or led to approval.

Multiple sclerosis

In a double-blind pilot, Roullet and colleagues randomized 40 people with active, moderately disabling multiple sclerosis to subcutaneous nonathymulin or placebo for 6 months, with another 6 months of follow-up. Disability, walking and functional scores did not differ between groups, and the authors judged the treatment ineffective in this setting.

Uses with no human data

We found no human study of thymulin for muscle mass, strength, injury recovery, weight loss, hair growth, cognition or athletic performance. There is also no registered treatment trial of thymulin on ClinicalTrials.gov. For people on GLP-1 medicines worried about losing lean mass, the evidence on what does help is covered in our guide to GLP-1s and muscle loss; thymulin is not part of it.

5. What does the animal research suggest?

Most recent thymulin work is in rodents, and its central finding is that the effect flips with dose. A 2006 review by Dardenne, Saade and Safieh-Garabedian summarizes it:

• Tiny local doses made pain worse, in rats. Injecting as little as 0.5 ng into a rat’s paw produced hyperalgesia, an exaggerated sensitivity to pain, and raised the inflammatory signals IL-1β and nerve growth factor, as reported by Safieh-Garabedian and colleagues.
• Larger systemic doses eased inflammatory pain, in rats. Doses of 1–25 µg of thymulin, or of a synthetic analogue called PAT, reduced pain and cytokine levels after an endotoxin challenge. Thymulin injected into the brain also blunted endotoxin-driven pain.

A separate line of work used gene therapy. Per the Reggiani review, researchers delivered a synthetic gene for a thymulin analogue (metFTS) by viral vector into thymus-lacking “nude” mice at birth. The single injection restored circulating thymulin and prevented the low LH and FSH levels and ovarian damage these mice usually develop. That is an experimental gene treatment in mice, not a peptide injection in people, and it does not establish any fertility benefit in humans.

6. Is thymulin legal or FDA approved?

• No approved drug. We found no FDA-approved thymulin product. The single DailyMed listing is a sublingual “Thymulinum 9C” homeopathic pellet labeled for “immune support” and classed as an unapproved homeopathic product. A homeopathic dilution is not what the clinical trials tested.
• Not a 503A compounding substance. Thymulin is absent from the bulk substances US pharmacies may compound under section 503A.
• Not on FDA’s safety-risk list either. The FDA list of compounding substances that may present significant safety risks, updated April 22, 2026, includes thymosin alpha-1 and TB-500 but not thymulin. Being left off that list says nothing about safety.
• Covered by WADA’s catch-all ban. The 2026 WADA Prohibited List does not name thymulin, but its S0 class bans at all times any pharmacological substance without current regulatory approval for human therapeutic use. With no approval found anywhere, thymulin would fall under S0.

7. What dose was studied, and what is thymulin’s half-life?

The only human doses with published outcomes are the 1, 5 and 10 mg/day nonathymulin arms of the 1987 rheumatoid arthritis trials, where 5 mg/day performed best. The multiple sclerosis trial gave nonathymulin subcutaneously. These are details of decades-old disease trials, not an approved or validated regimen, and they say nothing about doses used for wellness or performance.

No published study has measured how injected thymulin is absorbed, distributed or cleared in humans, so its half-life in people is unknown. Any half-life figure attached to a research product is not backed by a human pharmacokinetic study. Our explainer on peptide half-life tracking covers why a decay curve is only as reliable as the measured half-life behind it.

8. What are the side effects and risks?

Human reports are thin. The arthritis trials described adverse effects as minimal, and the multiple sclerosis trial found no significant side effects over 6 months (Amor et al.; Roullet et al.). Both were small with short follow-up, their abstracts give no event rates, and no modern safety database exists.

The effect may depend on dose. In rats, low doses increased pain and inflammatory mediators while higher doses reduced them (Safieh-Garabedian et al.). Whether this holds in people is unknown, but it argues against describing thymulin as simply anti-inflammatory.

Product quality is uncontrolled. Research-grade thymulin sits outside the regulated drug supply. Because activity depends on bound zinc, the amount of peptide, its zinc content and its purity all matter, and none is guaranteed. There are no data in pregnancy, breastfeeding, children, autoimmune disease, cancer, or people taking other medicines.

9. Interactions, GLP-1 medicines and what you can measure

No study has paired thymulin with semaglutide, tirzepatide or any other GLP-1 drug, so there are no interaction data in either direction. Thymulin has no demonstrated effect on body weight, appetite or blood sugar.

The research does show which body systems are linked to thymulin. Its levels move with thyroid function in people (Fabris et al.) and with growth hormone status (Reggiani et al.), which is relevant context for anyone also using growth hormone or having thyroid levels checked. In the cited studies, serum thymulin activity and zinc status were measured in research settings, and zinc repletion, rather than the peptide, was what restored low thymulin.

If you log any supplement or peptide alongside a GLP-1 medicine, recording start dates, doses and symptoms helps you and a clinician review a timeline. A log cannot show that thymulin did anything, because no trial has defined what effect to expect.

10. Thymulin FAQ

• What is thymulin used for?

  In the body, thymulin is a thymus hormone involved in T-cell development. As a drug, the synthetic form (nonathymulin) was tested in small 1980s trials in rheumatoid arthritis and multiple sclerosis, and it was never approved. Online sellers market it for immune support, recovery and anti-aging, but no human study supports those uses.

• Is thymulin legal?

  It is not an FDA-approved drug and is not on the list of bulk substances US pharmacies may use for 503A compounding. The only DailyMed listing is a homeopathic 9C pellet classed as an unapproved homeopathic product. Research-chemical thymulin sits outside the regulated drug supply.

• Is thymulin banned in sports?

  WADA's 2026 list does not name thymulin. Its S0 class prohibits at all times any pharmacological substance with no current government approval for human therapeutic use, and thymulin appears to have no such approval, so it would fall under S0.

• What are the side effects of thymulin?

  The 1980s trials reported minimal adverse effects in rheumatoid arthritis and no significant side effects over 6 months in multiple sclerosis, but they were small and short. In rats, low doses increased pain sensitivity while higher doses reduced it. There is no modern human safety database.

• How long does thymulin stay in your system?

  Nobody knows. No study of injected thymulin's absorption, distribution or clearance in humans has been published, so its half-life in people is unknown.

• What is the thymulin dosage?

  There is no approved dose. The rheumatoid arthritis trials compared nonathymulin at 1, 5 and 10 mg/day and found 5 mg the most effective of the three. That is a historical trial detail, not a validated or recommended dose.

• Can thymulin be used with semaglutide or tirzepatide?

  No study has tested thymulin alongside semaglutide, tirzepatide or any GLP-1 medicine, so there are no interaction or safety data for the combination. Thymulin has no demonstrated effect on weight or on preserving muscle during weight loss.

• Is thymulin the same as thymosin alpha-1 or thymalin?

  No. Thymulin is a nine-amino-acid zinc-binding peptide. Thymosin alpha-1 is a 28-amino-acid peptide, thymosin beta-4 has 43 amino acids, and thymalin is a mixture of peptides extracted from calf thymus. Each has its own, separate evidence base.

11. Sources