Thymosin Alpha-1

Tα1, thymalfasin, Zadaxin (brand name), TA1

Immune & bioregulators

Awaiting medical reviewEN ES DE FR PT ZH+ Follow for updates

Note on this profile. Thymosin alpha-1 (thymalfasin, Zadaxin) is an approved prescription medicine in more than 30 countries — including China, Italy and several others — for hepatitis B and as a vaccine adjunct, though not in the US, UK or most of the EU. This page explains the published science. Use outside a prescription, including compounded or grey-market versions, carries real risks discussed below.

Summary

Class: Naturally occurring 28-amino-acid peptide hormone originally isolated from the thymus; the approved product is a synthetic, N-terminally acetylated copy
Mechanism: Boosts the maturation and function of T cells, dendritic cells and natural killer cells, largely by acting on Toll-like receptors (TLR2 and TLR9), and helps rebalance an over- or under-active immune response
Routes studied: Subcutaneous (approved and in trials); intramuscular and intravenous (older studies); community subcutaneous
Dose range reported: Approved label: 1.6 mg subcutaneous twice weekly, typically 6–12 months for chronic hepatitis B; same dose 2–4 weeks as vaccine adjunct. Sepsis trials: 1.6 mg twice daily for 7 days. Community: 1.5–1.6 mg twice weekly, or 0.5–1 mg daily for short courses, all off-label or unapproved
Half-life: About 2 hours in plasma after subcutaneous injection; peak at ~1–2 hours. Immune effects outlast the plasma presence
Storage: Approved product: lyophilised vials, refrigerate (2–8°C). Reconstituted: use promptly per label. Research vials: refrigerate; community practice is use within ~4 weeks
Regulatory status: Approved in 30+ countries (China, Italy, Argentina, Mexico, Philippines and others); not approved in the US, UK, Canada, Australia. See region table

Doses are as reported in studies or by the community — never recommendations.

1What it is

Thymosin alpha-1 is a 28-amino-acid peptide first isolated in 1977 by Allan Goldstein's group from thymosin fraction 5, a crude thymus extract. The thymus is the gland where T cells mature, and Tα1 is one of the signals it uses to do that. The body makes it by cutting it from a larger protein, prothymosin alpha.

A synthetic version (thymalfasin, brand Zadaxin, developed by SciClone) has been approved since the 1990s in a growing list of countries, mainly for chronic hepatitis B and as an adjunct to vaccines in people with weak immune responses. It has been studied in hepatitis C, several cancers (as an adjunct to chemotherapy or interferon), sepsis, and most recently in severe COVID-19, where Chinese observational studies attracted attention. In the US it has orphan designations but no approval, and the FDA placed it in Category 2 of its compounding bulk-substances list in 2023, restricting compounding.

Of all the "immune peptides" discussed online, Tα1 has by far the most human data.

2How it's thought to work

TLR signalling. Tα1 acts as an at Toll-like receptors 2 and 9 on dendritic cells and other innate immune cells, triggering maturation and release of cytokines such as IL-12 that push T cells toward a Th1 (anti-viral, anti-tumour) response (Romani 2007).

T-cell maturation. increases the number and function of CD4+ and CD8+ T cells and reverses some features of T-cell exhaustion in chronic infection.

NK and dendritic cell function. enhances natural killer cell activity and antigen presentation.

Immune balancing. in states of excessive inflammation (sepsis, severe COVID-19) it appears to reduce damaging cytokine release while supporting cell-mediated immunity, via induction of indoleamine 2,3-dioxygenase and regulatory T cells. "Immunomodulator" rather than simply "booster" is the accurate description.

Direct effects on infected or tumour cells. increases MHC class I expression and viral antigen display, making infected cells more visible to T cells.

Acts on Toll-like receptors on dendritic cells, which then help T cells mature and natural killer cells become more active.Schematic — not to scale

3What the research shows

Chronic hepatitis B

Multiple in the 1990s–2000s of 1.6 mg twice weekly for 6 months showed higher rates of sustained loss of hepatitis B viral DNA and normalisation of liver enzymes than controls, with a delayed response pattern (effects increasing after treatment ended). A meta-analysis found roughly double the sustained response rate vs no treatment (Chan 2001, Aliment Pharmacol Ther). Benefit is modest by modern antiviral standards and it is now mostly used in combination. [3]

Graded A (mixed)

Hepatitis C

Combined with interferon ± ribavirin, Tα1 improved response rates in some trials of difficult-to-treat patients (Sherman 1998; Ciancio 2012, Antivir Ther) but not consistently. Largely superseded by direct-acting antivirals.

Vaccine adjunct

In haemodialysis patients and older adults, Tα1 improved antibody response to hepatitis B and influenza vaccines in randomised trials (Carraro 2012, Vaccine; earlier studies 1990s). This is an approved use in several countries. [7]

Graded A/B

Cancer (adjunct)

RCTs in melanoma (Maio 2010, J Clin Oncol — Tα1 plus dacarbazine, improved response and a trend to survival), hepatocellular carcinoma after resection or ablation (reduced recurrence in several Asian trials), and lung cancer alongside chemotherapy. Benefit is modest and not all trials were positive; not approved for oncology in most places. [4]

Graded A (mixed)

Sepsis

The ETASS trial (n=361) in China reported reduced 28-day mortality with Tα1 twice daily for 7 days, though not quite reaching conventional significance (Wu 2013, Crit Care). A large follow-up RCT (TESTS, n≈1,100) reported no significant mortality reduction in 2024 †. [5]

Graded B/A (mixed)

COVID-19

Retrospective Chinese cohorts in 2020 reported lower mortality in severe COVID-19 with Tα1 (Liu 2020, Clin Infect Dis). Subsequent analyses were mixed and an RCT in the US (ThymoCOVID) did not show a clear benefit †. [6]

Graded C/D/—

Cystic fibrosis, immunodeficiency, chronic fatigue, "immune optimisation"

Mouse models of cystic fibrosis showed Tα1 corrected some CFTR-related inflammation (Romani 2017, Nat Med), prompting human trials that did not confirm the effect. Community use for general immune support, Lyme or long COVID has no controlled evidence.

4Reported side effects and interactions

Literature-reported

one of the best-tolerated immunomodulators studied. In hepatitis B trials adverse events were similar to placebo; the most common were injection-site discomfort and transient redness. No dose-limiting toxicity was found in trials up to 16 mg. Over 20 years of post-marketing use in approved countries without a major safety signal.

Community-reported

injection-site redness, mild fatigue or flu-like feeling in the first days, occasionally a transient rash. Some report improved subjective wellbeing or fewer infections; this is unverified anecdote.

Theoretical. any immunostimulant carries a theoretical risk of flaring autoimmune disease or provoking rejection in transplant recipients; the balancing action makes this less likely than with interferons, but caution is standard. Pregnancy and breastfeeding: no adequate data.

Interactions. no pharmacokinetic interactions established. Immunosuppressant medicines (ciclosporin, tacrolimus, high-dose corticosteroids) oppose its action in principle. Used alongside interferon, chemotherapy and antivirals in trials without recognised interactions.

Markers researchers commonly monitor

Marker	Why it's watched
CBC with differential, including absolute lymphocyte count	the direct cellular target.
Lymphocyte subsets (CD3, CD4, CD8, CD4/CD8 ratio, NK cells)	the measures used in trials to show T-cell effects.
Liver enzymes (ALT, AST) and viral load	the approved indication endpoints in hepatitis B.
CRP and IL-6	in inflammatory or infectious contexts, to track the immunomodulatory rather than stimulatory direction.
Antinuclear antibodies and thyroid function	baseline screens where there is any history of autoimmunity, given the theoretical flare risk.

Free for everyone. Safety information is never behind a paywall.

5Reconstitution and handling

The approved product is a 1.6 mg vial with 1 ml sterile water per the label. Research vials are commonly 5 mg or 10 mg; reconstitute with and swirl gently.

Open in calculator, pre-loaded →

6Commonly studied alongside

Interferon-alpha and ribavirin (hepatitis trials), chemotherapy (oncology trials), vaccines. In the community: thymalin, LL-37, BPC-157 (no combined studies).

Informational cross-links. Not stack recommendations.

7Regulatory status by region

Region	Status (checked —)
United States	Not FDA-approved. Orphan drug designations (hepatitis B, hepatocellular carcinoma, others). Placed in Category 2 of FDA's 2023 compounding bulk-substances list
European Union	Not centrally authorised. Nationally approved in Italy (hepatitis B, vaccine adjunct) †
United Kingdom	Not licensed
Australia	Not approved
South Africa	Not registered †
Sport	Not specifically named by WADA; as a non-approved substance in most jurisdictions it falls under S0 †

8Open questions

Where does Tα1 fit now that hepatitis B and C have potent antivirals?
Does it meaningfully reduce mortality in sepsis or severe viral pneumonia? Large trials have been equivocal.
Does periodic use in healthy people change infection rates or immune ageing? No controlled data.

9References

1Goldstein AL et al. (1977). Thymosin α1: isolation and sequence analysis of an immunologically active thymic polypeptide. Proc Natl Acad Sci USA. PubMed · DOI
2Romani L et al. (2007). Thymosin α1: an endogenous regulator of inflammation, immunity, and tolerance. Ann N Y Acad Sci. PubMed · DOI
3Chan HLY, Tang JL, Tam W, Sung JJY (2001). The efficacy of thymosin in the treatment of chronic hepatitis B virus infection: a meta-analysis. Aliment Pharmacol Ther. PubMed · DOI
4Maio M et al. (2010). Large randomized study of thymosin α1, interferon alfa, or both in combination with dacarbazine in patients with metastatic melanoma. J Clin Oncol. PubMed · DOI
5Wu J et al. (2013). The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial. Crit Care. PubMed · DOI
6Liu Y et al. (2020). Thymosin alpha 1 reduces the mortality of severe coronavirus disease 2019 by restoration of lymphocytopenia and reversion of exhausted T cells. Clin Infect Dis. PubMed · DOI
7Carraro G et al. (2012). Thymosin-alpha 1 (Zadaxin) enhances the immunogenicity of an adjuvated pandemic H1N1v influenza vaccine (Focetria) in hemodialyzed patients: a pilot study. Vaccine. PubMed · DOI
8King R, Tuthill C (2016). Immune modulation with thymosin alpha 1 treatment. Vitam Horm. PubMed · DOI
9FDA (2023). Bulk drug substances for compounding — thymosin alpha-1 category 2 listing. PubMed

References are being resolved to PubMed/DOI identifiers; links search PubMed for the citation until then.

† Being confirmed by our reviewers against current sources.

10Community

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11Page history

25 Oct 2026Profile published — awaiting medical review

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