Thymosin alpha-1 vs thymulin
Last updated: October 4, 2026 · 6 min read · By the Grey Peptides Editorial Board
- Both come from the thymus, but thymosin alpha-1 is an approved drug in about 35 countries and thymulin is not approved anywhere.
- Thymosin alpha-1 has randomised trials: some positive in hepatitis, a borderline add-on result, and a large neutral trial in sepsis.
- Thymulin's human record is mostly measurement, how its level changes with zinc and age, plus four patients given it in 1983.
- Neither is FDA-approved, and immune-boosting claims for either go beyond what the trials show.
Side by side
Thymosin alpha-1 High and thymulin Low are both peptides first found in thymus tissue 1. The table is read from our encyclopedia entries.
| Field | Thymosin α1 | Thymulin |
|---|---|---|
| Encyclopedia entry | Thymosin α1 Full entry | Thymulin Mid-length entry |
| Molecule class | Peptide | Peptide |
| Category | Immune | Immune |
| FDA status | Not FDA Approved | Research Chemical |
| Approved elsewhere | ~35 countries, not the US | None recorded |
| Evidence grade | High | Low |
| Half-life | ≈ 2 hours | About 10 minutes in sheep; not measured in people |
| Formula | C129H215N33O55 | C33H54N12O15 |
| Molecular weight | 3,108.3 g/mol | 858.9 g/mol |
| WADA 2026 | Unsettled (S0 may apply) | Prohibited (S0 catch-all) |
| WADA 2027 | Unsettled (S0 may apply) | Prohibited (S0 catch-all) |
| In one line | A thymic peptide approved as Zadaxin in about 35 countries; its hepatitis trials were mixed, and its largest trial, in 1,106 sepsis patients, found no effect on death. | A zinc-dependent thymic nonapeptide, measured in people far more often than it has ever been given to them. |
| Mechanism | Modulates both innate and adaptive immunity. Activates TLR2 and TLR9 on dendritic cells and monocytes, driving NF-κB activation and production of IL-12, TNF-α, and IL-6. Promotes dendritic cell maturation, T-cell differentiation (particularly Th1), and enhances NK cell cytotoxicity. Restores immune function in immunocompromised states (hepatitis B/C, sepsis, post-chemotherapy) and enhances vaccine responses in elderly and hemodialysis populations. | Zinc-bound thymulin promotes T-cell maturation (particularly CD4+ and CD8+ differentiation from thymic precursors), enhances NK cell cytotoxicity, and modulates IL-2 production. Activity absolutely depends on zinc binding — in zinc-deficient states serum immunoreactive thymulin remains but loses biological activity. |
| Sources in the entry | 17 | 9 |
| Study cards | 15 | None (short entry) |
| Dosage page | Dosage page | None |
Two thymic peptides
The thymus, behind the breastbone, is where T cells learn to tell the body's own tissue from invaders. It shrinks with age, which is why its peptides attract interest as possible immune restorers. Thymosin alpha-1 is a 28-amino-acid peptide originally purified from a thymus extract and now made synthetically as thymalfasin. Thymulin is a nine-amino-acid hormone made by thymic cells that only works when bound to zinc; removing the zinc destroys its activity and adding it back restores it, which is how it got its name (laboratory study) 2.
Thymosin alpha-1: an approved drug with mixed trials
Thymosin alpha-1 is approved in more than 35 countries, including Italy and China, as Zadaxin for chronic hepatitis B and C and as an immune enhancer; in the US it holds orphan designations but no marketing approval (dataset) 1.
Its trials are mixed. In 98 patients with chronic hepatitis B, 26 weeks of treatment led to a complete virological response at 18 months in 40.6%, against 9.4% untreated, although the groups had looked similar at the end of therapy (randomised trial) 3. Added to interferon in a double-blind trial in 98 patients, it raised HBeAg loss to 45.8% from 28.0%, a difference that missed statistical significance (P = 0.067) (randomised trial) 4. In hepatitis C, added to interferon, it doubled end-of-treatment response in 109 patients (randomised trial) 5.
The largest trial was negative. In TESTS, 1,106 adults with sepsis at 22 Chinese centres received thymosin alpha-1 or placebo for seven days; 28-day mortality was 23.4% against 24.1%, and no secondary or safety outcome differed (randomised trial) 6. Our thymosin alpha-1 entry covers its other studies, including COVID-19.
Thymulin: measured more than tested
Most human research on thymulin measures it rather than gives it. In mildly zinc-deficient adults, blood thymulin fell even while blood zinc looked normal, and rose again with zinc supplements, which made thymulin a proposed marker of zinc status (human study) 7. In 290 children in rural Nepal, thymulin levels at ages 9 to 13 tracked birth timing and body size (human study) 8. A 2026 study identified thymulin as a thymic factor that declines with age and found it dampened inflammatory immune cells; in mice it improved tumour control alongside an immunotherapy drug (animal and human-cell study) 9.
The only published report of giving thymulin to people involves four cancer patients in 1983, given 10 µg/kg intravenously every three days: natural-killer cell activity rose in the two who started low and fell in the two who started high, matching what the researchers saw in blood cells in the dish (case series) 10. Our thymulin entry has the full record.
What the difference means
The gap between these two is not subtle. Thymosin alpha-1 has been tested in randomised trials involving well over a thousand patients and approved by several national regulators, even if its strongest results are in hepatitis and its largest trial found no benefit in sepsis (randomised trial) 6. Thymulin has never been through a controlled trial in people. Thymulin's zinc dependence also means that, in principle, zinc status may matter more than adding the peptide, since thymulin activity recovered with zinc alone in deficient adults (human study) 7.
The immune-boosting claims
Both are sold online as research peptides with claims of immune support, anti-ageing and recovery from illness. Thymosin alpha-1's trials show effects on hepatitis outcomes in some studies, not a general boost to immunity, and the sepsis trial, where an immune benefit would matter most, was neutral (randomised trial) 6. Thymulin's claims rest on laboratory work and the age-related decline in its levels (animal and human-cell study) 9. A falling level with age does not show that replacing it helps.
Research-grade products of either carry the quality risks of any unregulated peptide, and our marketplace article explains what testing of such products has found.
Status
Thymosin alpha-1 is approved in about 35 countries but not by the FDA; thymulin is not approved anywhere and has no FDA application (dataset) 1. Neither can be prescribed in the US as an approved product, and our category guide covers where peptides like these stand for compounding.
How they compare (as of October 4, 2026)
Thymosin alpha-1 and thymulin share an origin in the thymus and little else in evidence. Thymosin alpha-1 is an approved drug abroad, with randomised trials that are positive in some hepatitis settings, borderline in others, and neutral in a 1,106-patient sepsis trial. Thymulin is a zinc-dependent hormone whose human record is measurement plus four patients treated in 1983. Neither is FDA-approved, and claims of general immune boosting go beyond what either has shown.
Frequently asked questions
What is the difference between thymosin alpha-1 and thymulin?
Both come from the thymus. Thymosin alpha-1 is a 28-amino-acid peptide approved abroad as Zadaxin; thymulin is a zinc-dependent nine-amino-acid hormone that has never been through a controlled trial.
Is thymosin alpha-1 approved?
In about 35 countries, for hepatitis B and C and as an immune enhancer, but not by the FDA.
Did thymosin alpha-1 help in sepsis?
No. In the 1,106-patient TESTS trial, 28-day mortality was 23.4% with thymosin alpha-1 and 24.1% with placebo.
Has thymulin been tested in people?
Only in four cancer patients in 1983; most human research measures its blood levels, which fall in zinc deficiency.
Related on Grey Peptides
Sources
- Grey Peptides dataset records for thymosin alpha-1 (approved in 35+ countries as Zadaxin/thymalfasin; FDA orphan designations; not FDA-approved) and thymulin (not approved anywhere; no Drugs@FDA application); read October 4, 2026.
- Dardenne, M., et al. (1982). Contribution of zinc and other metals to the biological activity of the serum thymic factor. Proc Natl Acad Sci U S A, 79(17), 5370-3. PMID: 6957870
- Chien, R. N., et al. (1998). Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial. Hepatology, 27(5), 1383-7. PMID: 9581695
- Lim, S. G., et al. (2006). A randomized, placebo-controlled trial of thymosin-alpha1 and lymphoblastoid interferon for HBeAg-positive chronic hepatitis B. Antivir Ther, 11(2), 245-53. PMID: 16640105
- Sherman, K. E., et al. (1998). Combination therapy with thymosin alpha1 and interferon for the treatment of chronic hepatitis C infection: a randomized, placebo-controlled double-blind trial. Hepatology, 27(4), 1128-35. PMID: 9537454
- Wu, J., et al. (2025). The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ, 388, e082583. PMID: 39814420
- Prasad, A. S., et al. (1988). Serum thymulin in human zinc deficiency. J Clin Invest, 82(4), 1202-10. PMID: 3262625
- Palmer, A. C., et al. (2020). Prenatal and childhood exposures are associated with thymulin concentrations in young adolescent children in rural Nepal. J Dev Orig Health Dis, 11(2), 127-135. PMID: 31475652
- Kanemaru, H., et al. (2026). Thymulin restrains age-associated myeloid inflammation and enhances cancer immunotherapy. Nat Commun, 17(1). PMID: 42481458
- Dokhelar, M. C., et al. (1983). Effect of a synthetic thymic factor (facteur thymique serique) on natural killer cell activity in humans. Int J Immunopharmacol, 5(4), 277-82. PMID: 6195118
Educational information, not medical advice. Each dose in this guide names its source, an approved label or a published study. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose.
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