Reviewed & approved by Dr. Nova Reyes · Last checked 2026-10-15. ← Back to Evidence Library
Thymosin alpha-1 (thymalfasin): what the evidence says
At a glance
What it is: a 28-amino-acid peptide first found in the thymus, the gland where some immune cells mature. The lab-made version is called thymalfasin and is sold as the prescription drug Zadaxin in Italy and China (other countries per the company only). Gray-market "TA1" vials are sold online for "immune support," anti-aging and recovery. R1, R2
What the evidence says: for chronic hepatitis B, a 2026 Cochrane review found it may lower deaths, but the evidence is very low certainty. In the largest trial ever done, a placebo-controlled study of 1,106 adults with sepsis, it did not lower deaths. COVID-19 results come from conflicting hospital record reviews. There are no trials in healthy people. R5, R6, R10–R12
Biggest risks: in trials it was generally well tolerated, In one large sepsis trial, deaths overall did not differ. In a planned subgroup analysis, people under 60 had more deaths on it (hazard ratio 1.67; interaction p=0.01). This may be chance and wasn't the trial's main result. The bigger risk for gray-market users is not knowing what's in the vial. R5, R6
| Claim | Rating |
|---|---|
| Human Chronic hepatitis B (approved use in China and elsewhere) | Very limited (mixed results): Cochrane 2026, very low certainty for most outcomes; trials inconsistent R5, R7 |
| Human Chronic hepatitis C (with interferon) | Very limited: one 109-person placebo-controlled trial; better response at the end of treatment, but lasting response was low in both groups; the interferon regimen is now obsolete R8 |
| Human Sepsis | Tested, not shown: large phase 3 placebo-controlled trial (TESTS, 1,106 people) found no effect on 28-day deaths. Partly funded by SciClone, Zadaxin's maker R6 |
| Human COVID-19 | Very limited (mixed results): hospital record reviews only, conflicting; no completed randomized trial found R10–R12 |
| Human Better vaccine response (elderly, dialysis) | Very limited: small trials measuring antibody levels, not infections prevented R9, R13 |
| Unknown "Immune support", anti-aging, recovery in healthy people (gray-market use) | No human data (nothing at all in trials) |
| Regulatory | Approved in Italy and China (official records); not FDA-approved · FDA advisers voted 17–4 against adding it to the 503A compounding list (Dec 2024); no final FDA decision found · 503B: Category 3 · WADA 2026: not named R3, R14–R17 |
| Established human dose | Only for approved uses, under prescription, in countries where approved. Unknown No established dose for other uses |
Evidence verdict: Hepatitis B: Very limited (mixed results) · Hepatitis C: Very limited · Sepsis: Tested, not shown · COVID-19: Very limited (mixed results) · Vaccine response: Very limited · Immune support, anti-aging and recovery in healthy people: No human data (nothing at all) Card verdict: Very limited (hepatitis B/C, COVID-19, vaccine response; mixed results) · Sepsis: Tested, not shown · Immune support, anti-aging, recovery in healthy people: No human data Card note: Varies by use, see page
This page reports what studies and approved labels used. It is not dosing advice.
Legend: HUMAN data · ANIMAL / LAB data · UNKNOWN · UNVERIFIED: not yet confirmed against a primary source
What "No human data" means here: for general immune support, anti-aging or recovery in healthy people, we found nothing at all in human trials.
What is it?
Thymosin alpha-1 is a natural peptide made from a larger protein (prothymosin alpha). In lab and patient studies it affects T cells and dendritic cells, parts of the immune system that fight viruses. A change in immune-cell counts or markers is not a health benefit by itself. What matters is whether people get better, which is what the trials below test. R1, R6
Where it's approved (country by country)
| Country / region | Product | Approved uses | Year | How we checked |
|---|---|---|---|---|
| Italy | Zadaxin (timosina alfa 1), powder and solvent for injection, prescription only; product details in the AIFA medicines database record (search "Zadaxin", AIC 028364) | Caution [UNVERIFIED: Italian indication; the AIFA record doesn't state it] | Current pack authorised May 16, 1996 (the company says first approval was 1993 UNVERIFIED) | AIFA medicines database (official), AIC 028364, holder SciClone Pharmaceuticals Italy, status "authorised", checked Oct 15, 2026 R21 |
| China | Zadaxin (日达仙, thymalfasin for injection); product details in the NMPA registration record R18 | Caution [UNVERIFIED: indications on the current Chinese label] | Imported-drug registration 国药准字HJ20171177 (formerly H20171177), issued May 6, 2022 (corrected Oct 14, 2022), valid to May 5, 2027. First launch Dec 1996 per trade press UNVERIFIED | National drug data center registration record (government-run database of NMPA data, read in Chinese), checked Oct 15, 2026 R18; trade press R2 |
| United States | — | Not approved | — | No entry in Drugs@FDA (openFDA query, Oct 15, 2026) R14 |
| European Union (central) | — | Not centrally authorised | — | Not in the EMA's list of centrally authorised medicines (checked Oct 15, 2026) |
Removed from this table (couldn't confirm with a regulator or other official source): Singapore and the Philippines (trade press only), Argentina, Peru and Kuwait (company press release only), and the company's "over 30 countries" claim.
The approved medicine: what its trials showed
This section covers thymalfasin as used in clinical trials, mostly in China, Taiwan, Italy and the US.
Human Chronic hepatitis B: - A Taiwan trial (98 people, no placebo, untreated control group) found more people cleared the virus markers 18 months after starting a 26-week course (40.6%) than untreated controls (9.4%). No significant side effects were seen. R7 - Cochrane review (Sept 2026): across 10 randomized trials (1,349 people; 4 funded by industry), thymalfasin "may reduce" all-cause death (risk ratio 0.53, meaning about half the risk; 3 trials, 907 people) and serious adverse events, but the certainty was very low for all outcomes except serious adverse events (low). The authors are "not sure" it helps. Histology (liver tissue) showed no clear improvement. R5 - Today hepatitis B is treated with antiviral pills, which most of these older trials did not use.
Human Chronic hepatitis C: a US double-blind, placebo-controlled trial (109 people) added thymalfasin to interferon. At the end of treatment, liver enzymes normalised in 37.1% on the combination vs 16.2% on interferon alone (p=0.04). Lasting responses were low: 14.2% vs 8.1% (the abstract gives no significance test). Interferon regimens have since been replaced by highly effective antiviral pills. R8
Human Sepsis (TESTS): a phase 3 trial (large studies confirming benefit and safety before approval) at Chinese hospitals randomized 1,106 adults with sepsis to thymalfasin or placebo for 7 days. Deaths at 28 days: 23.4% vs 24.1% (hazard ratio 0.99, 95% CI 0.77–1.27). No secondary or safety outcome differed. A subgroup under age 60 did worse on thymalfasin (hazard ratio 1.67). The authors flagged this as possible but not proven. An earlier, smaller, single-blind trial (ETASS, 361 people, saline control) had shown a borderline benefit (26.0% vs 35.0%, p = 0.062) that the larger trial did not confirm. R6, R19 - Who paid: TESTS was supported by Sun Yat-sen University, a Guangdong research center and SciClone Pharmaceuticals (Zadaxin's maker); 12 authors received SciClone grants and 3 received consulting fees from SciClone and other companies. ETASS was funded by Sun Yat-sen University and Guangdong research grants, used SciClone's Zadaxin, and its authors declared no competing interests. R6, R19
Human COVID-19: all studies we found look back at hospital records, which can't separate the drug's effect from who was chosen to get it. - One Wuhan review (76 people) reported fewer deaths with thymalfasin (11% vs 30%). R10 - A larger 5-hospital review (2,282 people) found worse outcomes in treated patients, including after adjusting for other factors (higher non-recovery, odds ratio 1.5). R11 - A research letter reported no link to lower death rates. R12 - We found no completed randomized COVID treatment trial. A US prevention pilot in 194 dialysis patients (randomized, no placebo) has only a preliminary report: 3 deaths vs 7 in controls, too early and too small to conclude anything (Tuthill 2023, PMID 36881981).
Human Vaccine response: a double-blind placebo trial in 90 older men (1989) and a pilot in about 99 dialysis patients (2012, no placebo) measured antibody levels after flu vaccines, with better antibody responses reported. Higher antibody levels are a lab change, not proof that fewer people got sick. R9, R13
Does it work for gray-market uses?
Unknown "Immune support," anti-aging, recovery, long COVID in healthy people: no published trial. None of the results above were in healthy people, and FDA's advisers found "no compelling evidence demonstrating clinical effectiveness and safety" for the uses they reviewed. R15
Is it safe?
- Human In trials: ETASS reported "no serious drug-related adverse event." In TESTS, no safety outcome differed from placebo. The Taiwan hepatitis B trial saw "no significant side effects." R6, R7, R19
- Human Serious adverse events (problems reported after use, which may or may not have been caused by the drug): Cochrane found fewer on thymalfasin than on control (risk ratio 0.72, low certainty). R5
- Caution TESTS under-60 subgroup: more deaths on thymalfasin (hazard ratio 1.67, 95% CI 1.04–2.67). This may be chance, but it is a reason for caution. R6
- Dropouts vs placebo: in TESTS, 17 people (10 thymalfasin, 7 placebo) withdrew consent before receiving any study drug. No safety outcome differed between arms. R6
- Unknown The safety of long-term or repeated use in healthy people has not been studied.
Is it legal?
- FDA: not approved. There is no Drugs@FDA entry. R14
- Compounding (503A): at its Dec 4, 2024 meeting, FDA proposed that thymosin alpha-1 (free base and acetate) not be added to the 503A bulks list. Its advisory committee voted 17 to 4 against adding each form. R15 It does not appear in any category of FDA's 503A nominations list (May 14, 2026), and we found no final FDA decision. Caution [UNVERIFIED: absence of a final rule based on searches] Without a list entry, pharmacies have no approved basis to compound it. R16
- Compounding (503B): listed in Category 3, "nominated without adequate support" (list updated Mar 21, 2025). R17
- Athletes: not named on WADA's 2026 Prohibited List. Because it is approved in Italy and China, the S0 "non-approved substances" catch-all likely doesn't apply. Unknown This is our reading, not a WADA ruling. R20
What's in the vial?
Zadaxin is made under regulatory oversight. A gray-market "thymosin alpha-1" vial is not Zadaxin. It has no quality control and no guarantee of identity. It could contain the wrong compound, the wrong amount, impurities or bacterial toxins, or be fake (counterfeit). The trial results above don't transfer to it. We test retail vials blind under the Open Peptide Standard. See results at /tests/. A passing test covers one batch, tested on one date. It does not mean the compound itself is safe.
What do users report?
Self-report, not evidence.
Unknown TBD. We'll only list this once we can cite a public source.
Study details
R5–R13, R19 Human Human studies
| Study | People | Route | Dose used (study arm, not a recommendation) | Follow-up | Reported | Limitations | Citation |
|---|---|---|---|---|---|---|---|
| Wu 2025, TESTS (phase 3) | 1,106 adults with sepsis (1,089 analyzed), China | Subcutaneous every 12 h, 7 days | 1.6 mg every 12 h (full text) | 28 days | Deaths 23.4% vs 24.1% placebo; HR 0.99 | Part-funded by SciClone; under-60 subgroup worse | PMID 39814420 |
| Wu 2013, ETASS | 361 adults with severe sepsis, China | Subcutaneous | 1.6 mg twice daily for 5 days, then once daily for 2 days (full text) | 28 days | Deaths 26.0% vs 35.0% (p=0.062; RR 0.74, 95% CI 0.54–1.02) | Single-blind; saline control; university-funded | PMID 23327199 |
| Naing 2026, Cochrane review | 10 RCTs, 1,349 people with chronic hepatitis B | Various | Various | Various | Death RR 0.53 (very low certainty); SAE RR 0.72 (low) | Most trials high risk of bias | PMID 42713852 |
| Chien 1998 | 98 with chronic hepatitis B, Taiwan | Subcutaneous, twice weekly | 1.6 mg (26 or 52 wk) | 18 months | Complete response 40.6% (26 wk) vs 9.4% untreated | No placebo; small | PMID 9581695 |
| Sherman 1998 | 109 with chronic hepatitis C, US (3 arms, double-blind) | Subcutaneous, with interferon | 1.6 mg twice weekly | 26 wk treatment | End-of-treatment response 37.1% vs 16.2% IFN alone (p=0.04); sustained 14.2% vs 8.1% | Obsolete interferon regimen | PMID 9537454 |
| Liu Y 2020 | 76 severe COVID-19, Wuhan | — | — | In hospital | Deaths 11.1% vs 30.0% | Retrospective | PMID 32442287 |
| Liu J 2021 | 2,282 COVID-19 (306 treated), 5 hospitals | — | — | In hospital | Worse outcomes in treated group; adjusted non-recovery OR 1.5 (1.1–2.1) | Retrospective | PMID 34408744 |
| Gravenstein 1989 | 90 men aged 65–99, flu vaccine, double-blind placebo | Subcutaneous | 900 µg/m² twice weekly, 8 doses | 3–6 wk | Antibody response; no toxicity seen | Antibody levels only | PMID 2642497 |
| Carraro 2012 | ~99 hemodialysis patients (safety population), H1N1 vaccine, 3 arms, pilot | — | 3.2 or 6.4 mg | 168 days | Better antibody response than vaccine alone | Antibody levels only | PMID 22178096 |
R1–R4, R14–R18, R20, R21 Regulatory and approval sources (as of Oct 15, 2026)
- R2 The Pharmaletter, "First launch of SciClone's Zadaxin in China," Dec 9, 1996: https://www.thepharmaletter.com/first-launch-of-sciclone-s-zadaxin-in-china
- R3 SciClone Pharmaceuticals (Holdings), Hong Kong listing document, "History, reorganization and corporate structure" (2021; company source, used only for the company's own claims): https://www1.hkexnews.hk/listedco/listconews/sehk/2021/0219/9626734/2021021900034.pdf
- R4 SciClone press release, Apr 1998 (Italian approval acquired from Sclavo; Argentina, Peru, Kuwait approvals; company source, not used for any listed approval): https://www.newswit.com/en/j2z237y7omxmouvwx1lzfmtxfyel34sa
- R14 Drugs@FDA (openFDA, Oct 15, 2026): no match for thymalfasin or Zadaxin.
- R15 FDA, Pharmacy Compounding Advisory Committee, Dec 4, 2024, meeting minutes (saved copy): Final Summary Minutes, separate votes for free base and acetate, each Yes 4 / No 17 / Abstain 0: https://www.fda.gov/media/185642/download
- R16 FDA 503A nominations list (May 14, 2026): https://www.fda.gov/media/94155/download
- R17 FDA 503B nominations list (Mar 21, 2025), Category 3: https://www.fda.gov/drugs/human-drug-compounding/503b-bulk-drug-substances-list
- R18 China national pharmaceutical data center (NMPA registration data), 注射用胸腺法新 (Zadaxin) imported-drug registration 国药准字HJ20171177 (formerly H20171177), holder SciClone Pharmaceuticals Italy, issued 2022-05-06, valid to 2027-05-05 (Chinese): https://pharm.ncmi.cn/zysjk/ypjkyp/202312/t20231205_400230.html
- R21 AIFA (Italian Medicines Agency) medicines database: ZADAXIN, AIC 028364, holder SciClone Pharmaceuticals Italy S.r.l., status authorised; queried Oct 15, 2026: https://medicinali.aifa.gov.it/ (search "Zadaxin")
- R20 WADA 2026 Prohibited List: https://www.wada-ama.org/en/resources/world-anti-doping-code-and-international-standards/prohibited-list
Full reference list (PMIDs verified on PubMed, Oct 15, 2026)
- R1 Garaci E, et al. Front Med. 2024. doi:10.3389/fmed.2024.1388959. PMID 38903817 (review; three authors declare involvement in a SciClone-sponsored phase II trial of thymosin alpha-1).
- R5 Naing C, et al. Cochrane Database Syst Rev. 2026;9:CD014610. doi:10.1002/14651858.CD014610.pub2. PMID 42713852. No dedicated funding.
- R6 Wu J, et al. BMJ. 2025;388:e082583. doi:10.1136/bmj-2024-082583. PMID 39814420. Supported by the Sun Yat-sen University Clinical Research Program 5010, the Guangdong Clinical Research Center for Critical Care Medicine and SciClone Pharmaceuticals. Erratum: BMJ 2025;389:r1098.
- R7 Chien RN, et al. Hepatology. 1998;27(5):1383-7. doi:10.1002/hep.510270527. PMID 9581695.
- R8 Sherman KE, et al. Hepatology. 1998;27(4):1128-35. doi:10.1002/hep.510270430. PMID 9537454.
- R9 Gravenstein S, et al. J Am Geriatr Soc. 1989. doi:10.1111/j.1532-5415.1989.tb01561.x. PMID 2642497.
- R10 Liu Y, et al. Clin Infect Dis. 2020;71(16):2150-2157. doi:10.1093/cid/ciaa630. PMID 32442287.
- R11 Liu J, et al. Front Immunol. 2021;12:673693. doi:10.3389/fimmu.2021.673693. PMID 34408744.
- R12 Liu T, et al. Am J Emerg Med. 2022;53:252-253. doi:10.1016/j.ajem.2021.04.043. PMID 33896653.
- R13 Carraro G, et al. Vaccine. 2012. doi:10.1016/j.vaccine.2011.12.014. PMID 22178096.
- R19 Wu J, et al. Crit Care. 2013;17(1):R8. doi:10.1186/cc11932. PMID 23327199.
Disclaimer
This page is for education and harm reduction. It is not medical advice and not a recommendation to use thymosin alpha-1 outside a prescription in a country where it is approved. Please talk to a clinician you trust, especially if you have hepatitis, an immune condition, or are pregnant, or are a tested athlete. Seek care right away for a serious reaction, and report it to FDA MedWatch (https://www.fda.gov/safety/medwatch) or your national regulator.