Peptides / Immune and antimicrobial

Natural fragment · 28 amino acids · 3,108.3 Da

Thymosin alpha-1

Approved in Singapore, China +1Not banned in sport

Thymosin alpha-1 is a 28-amino-acid peptide cut from the protein prothymosin alpha. As thymalfasin (Zadaxin) it is approved in some countries but not by the FDA or EMA, and studies in people tested it on the immune system, inflammation and the liver. PepBank shows 603 results on thymosin alpha-1 from 107 studies in people, and 842 from animal and lab studies. The strongest evidence is a randomized trial in people. Data as of 2026-10-30.

Also known as Ta1, Tα1, Thymosin alpha 1, Thymosin alpha1, alpha1-Thymosin, Thymalfasin and 1 more

28 amino acids, from first to last1 changed amino acid

Evidence level: Some studies in people603 of 1,450 results come from studies in people.

Results in people

603

42% of 1,450 results

Results in animals

380

26% of 1,450 results

Results in lab cells

462

32% of 1,450 results

From computer models

under 1% of 1,450 results

Overview

Key points

Thymosin alpha-1 is a natural peptide fragment, 28 amino acids long, from the human protein prothymosin alpha.¹
In a randomized trial of 361 ICU patients with severe sepsis, 28-day mortality was 26.0% with thymosin alpha-1 and 35.0% with control, a marginally significant difference.²
Other randomized trials in people found no clear difference, including a trial in 690 people with hepatitis B cirrhosis and a trial in people with predicted severe acute necrotising pancreatitis.^3,4
As thymalfasin (Zadaxin), thymosin alpha-1 is approved in some countries for chronic hepatitis B, has no FDA or EMA approval, and is not named on the WADA 2026 Prohibited List.^1,5,6,7,8

Thymosin alpha-1 at a glance

What it is	Natural fragment, 28 amino acids
Approval	Approved outside the US and EU (Singapore, China, Philippines)
In sport	Not listed as banned by WADA
Studies	615 studies with results. 332 of them gave thymosin alpha-1, with 1,450 results. 603 in people380 in animals462 in lab cells5 from computer models
Best study in people	Randomized controlled trial with 690 people (2018)
Clinical trials	56 registered: 13 active or planned, 2 with posted results
Community use	General immune support and illness prevention (off-label); Lyme disease co-treatment, chronic fatigue and mold illness protocols (off-label, community claims); Chronic hepatitis B and C (approved use in some countries, with a prescriber)

The science

What is thymosin alpha-1?

Thymosin alpha-1 (thymalfasin) is a short natural peptide, a small chain of amino acids taken from the start of a human protein called prothymosin alpha.¹ It is described as a thymus peptide found in thymosin fraction 5 and is now made by synthesis.¹

Other names include Zadaxin, Tα1 and alpha1-Thymosin.¹ SciClone Pharmaceuticals is named as the developer of Zadaxin.⁵

Amino acids in the chain¹

The history of thymosin alpha-1

1977
The oldest paper on thymosin alpha-1 in PepBank is from 1977.⁹
1991May
The FDA gave SciClone Pharmaceuticals an orphan designation for chronic active hepatitis B, and the FDA lists it as not approved for that use.⁶
1993September
Singapore approved Zadaxin for chronic hepatitis B, with a patient surveillance programme.¹⁰
1996September
In China, the Ministry of Public Health licensed Zadaxin for chronic hepatitis B, and it launched there in January 1997.¹¹
2002July
The European Union granted SciClone Pharmaceuticals Italy an orphan designation for thymalfasin in hepatocellular carcinoma.⁷
2016September
The phase 3 TESTS trial in sepsis started in September 2016 and is listed as completed in March 2021, with an enrollment of 1,106 and no posted results.¹²

Thymosin alpha-1 structure and chemistry

The key facts about the molecule. Long codes are in the closed section below.

Sequence, 28 amino acidsFrom the first amino acid to the last

S1−DAAV5−DTSS−E10ITT+K−D15L+K−E+K+K20−EVV−E−E25A−EN

Darker means more water-repelling+ and − show charge in the bodyOutlined: changed amino acid

Structure

Thymosin alpha-1 is a chain of 28 amino acids with no ring, taken from prothymosin alpha, and it carries an acetyl group on the amino acid at the start of the chain.¹

Formula

C₁₂₉H₂₁₅N₃₃O₅₅

Molecular weight

3,108.3 g/mol

CAS number

62304-98-7

Target

Toll-like receptor 9 (gene TLR9): activation of TLR9/MyD88 signalling in plasmacytoid dendritic cells (direct binding not shown in the abstract)Evidence: primary literature (mouse cytomegalovirus model, 2007); ChEMBL mechanism of action: Unknown

Development

SciClone Pharmaceuticals (Zadaxin). Highest phase: past the trial stage (see status).

Identifiers

PubChem 16130571, ChEMBL CHEMBL2103979, UNII W0B22ISQ1C, DrugBank DB04900, UniProt P06454, PDB 2L9I

Full sequence, SMILES and InChIKey

Three-letter sequence
Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-OH

InChIKey
NZVYCXVTEHPMHE-ZSUJOUNUSA-N

SMILES
CC[C@H](C)[C@@H](C(=O)N[C@@H]([C@@H](C)O)C(=O)N[C@@H]([C@@H](C)O)C(=O)N[C@@H](CCCCN)C(=O)N[C@@H](CC(=O)O)C(=O)N[C@@H](CC(C)C)C(=O)N[C@@H](CCCCN)C(=O)N[C@@H](CCC(=O)O)C(=O)N[C@@H](CCCCN)C(=O)N[C@@H](CCCCN)C(=O)N[C@@H](CCC(=O)O)C(=O)N[C@@H](C(C)C)C(=O)N[C@@H](C(C)C)C(=O)N[C@@H](CCC(=O)O)C(=O)N[C@@H](CCC(=O)O)C(=O)N[C@@H](C)C(=O)N[C@@H](CCC(=O)O)C(=O)N[C@@H](CC(=O)N)C(=O)O)NC(=O)[C@H](CCC(=O)O)NC(=O)[C@H](CO)NC(=O)[C@H](CO)NC(=O)[C@H]([C@@H](C)O)NC(=O)[C@H](CC(=O)O)NC(=O)[C@H](C(C)C)NC(=O)[C@H](C)NC(=O)[C@H](C)NC(=O)[C@H](CC(=O)O)NC(=O)[C@H](CO)NC(=O)C

See charge, composition and 3D structure on the Scientific page

How does thymosin alpha-1 work?

Step 1In mouse and cell studies, thymosin alpha-1 activates Toll-like receptor signalling (TLR9/MyD88)

Step 2Dendritic cells become activated^1,13

Mouse and cell studies report that thymosin alpha-1 activates dendritic cells through Toll-like receptor signalling.¹ In a 2007 mouse study of cytomegalovirus infection, thymosin alpha-1 activated TLR9 and MyD88 signalling in plasmacytoid dendritic cells.¹³

In miceIn lab cells

ChEMBL records the mechanism of action as unknown.^1,13

The evidence

What thymosin alpha-1 studies show

Results grouped by what the studies measured. Each card shows where its results come from.

Some studies in people603 of 1,450 results come from studies in people.

Immune system and inflammation

672 results · 203 in people · 199 animal · 270 lab

In ICU patients with severe sepsis, a marker of immune function improved more with thymosin alpha-1 than with control on day 3, and in people with tuberculosis and diabetes, adding it to chemotherapy gave higher CD3+ T cell levels than chemotherapy alone.^2,14

Top results

In ICU patients with severe sepsis, a marker of immune function (monocyte HLA-DR) improved more with thymosin alpha‑1 than with control on day 3. (Critical care, 2013)
In people with tuberculosis and diabetes, thymosin alpha‑1 plus chemotherapy gave lower IL-4 in sputum than chemotherapy alone. (Pakistan journal of medical sciences, 2022)
In people with lung cancer, thymalfasin treatment lowered the share of immune-suppressing MDSC cells in tumor tissue compared with before treatment. (American journal of translational research, 2024)

Infections

151 results · 117 in people · 19 animal · 15 lab

In adults with hepatitis B cirrhosis, adding thymosin alpha-1 to entecavir made no clear difference in virus response at week 104, and in hepatitis C patients who had not responded to earlier treatment, adding it to standard treatment gave a similar cure rate to adding placebo.^3,15

Top results

In adults with HBeAg-positive chronic hepatitis B, adding thymosin alpha‑1 to interferon did not significantly increase HBeAg loss at 72 weeks versus interferon plus placebo. (Antiviral therapy, 2006)
In people with hepatitis B cirrhosis, adding thymosin α1 to entecavir made no clear difference in virus response at week 104. (Expert opinion on biological therapy, 2018)
In adults with acute necrotising pancreatitis and a higher lymphocyte count, thymosin alpha‑1 lowered the risk of infected pancreatic necrosis compared with placebo. (EClinicalMedicine, 2023)

Survival and serious illness

136 results · 116 in people · 20 animal

In a small trial of 86 adults with septic shock, adding thymosin alpha-1 to blood purification shortened the time in shock but did not change overall survival at follow-up.¹⁶

Top results

In ICU patients with severe sepsis, fewer died within 28 days with thymosin alpha‑1 than with control, but the difference was borderline. (Critical care, 2013)
In adults with septic shock, adding thymosin alpha‑1 to blood purification shortened the time in shock. (Alternative therapies in health and medicine, 2022)
In metastatic melanoma, people given thymosin alpha‑1 lived a median 9.4 months and controls 6.6 months, but the difference was not statistically significant. (Journal of clinical oncology, 2010)

Liver

41 results · 39 in people · 2 animal

In people with chronic hepatitis C, thymosin alpha-1 plus interferon cleared the virus in more people than interferon alone (37.1% versus 18.9%), while in adults with HBeAg positive chronic hepatitis B, adding it to interferon did not significantly increase HBeAg loss at 72 weeks.^17,18

Top results

In people with hepatitis B cirrhosis, adding thymosin α1 to entecavir made no clear difference in liver decompensation, liver cancer or death. (Expert opinion on biological therapy, 2018)
In adults with HBeAg-positive chronic hepatitis B, adding thymosin alpha‑1 to interferon made no significant difference to liver tissue changes compared with interferon plus placebo. (Antiviral therapy, 2006)
In people with chronic hepatitis C, thymosin alpha1 plus interferon gave more normal liver enzymes at treatment end than interferon alone (37.1% versus 16.2%). (Hepatology, 1998)

Cancer

99 results · 27 in people · 37 animal · 35 lab

In a small trial of 57 patients with liver cancer after surgery, median survival was longer with thymosin alpha-1 plus TACE but one-year recurrence did not change, and in metastatic melanoma the survival difference from control was not statistically significant.^19,20

Top results

In metastatic melanoma, more tumors responded with thymosin alpha‑1 added to dacarbazine and interferon alfa than with dacarbazine and interferon alfa alone. (Journal of clinical oncology, 2010)
In people with hepatitis B cirrhosis, adding thymosin α1 to entecavir made no clear difference in liver cancer. (Expert opinion on biological therapy, 2018)
In patients with liver cancer after surgery, adding thymosin alpha‑1 to TACE did not change one-year recurrence compared with TACE alone or surgery only. (Hepato-gastroenterology, 2004)

Lungs and breathing

21 results · 17 in people · 4 animal

In adults with a COPD flare-up, thymosin alpha-1 plus routine care improved blood oxygen more than routine care plus placebo, and in people with COPD fewer patients had flare-ups with thymosin alpha-1 than in the control group.^21,22

Top results

In adults with a COPD flare-up, thymosin alpha‑1 plus routine care improved blood oxygen more than routine care plus placebo. (Immunopharmacology and immunotoxicology, 2015)
In mice given radiation, no pleural effusion occurred with thymosin alpha‑1, while it occurred with radiation alone. (Zhongguo fei ai za zhi = Chinese journal of lung cancer, 2011)
In people with COPD, fewer patients had flare-ups with thymosin alpha‑1 than in the control group. (Sichuan da xue xue bao. Yi xue ban = Journal of Sichuan University. Medical science edition, 2008)

All 615 thymosin alpha-1 studies by area Open the Scientific page

Key thymosin alpha-1 studies

Studies in people come first, then studies in animals and in the lab.

People
Combination of entecavir with thymosin alpha-1 in HBV-related compensated cirrhosis: a prospective multicenter randomized open-label study
Wu et al. 2018 · Expert opinion on biological therapy · 690 people · cited by 15
9 results
People
Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial
Ke et al. 2022 · Intensive care medicine · 508 people · cited by 45
5 results
People
Association between pretreatment lymphocyte count and efficacy of immune-enhancing therapy in acute necrotising pancreatitis: a post-hoc analysis of the multicentre, randomised, placebo-controlled TRACE trial
Ke et al. 2023 · EClinicalMedicine · 502 people · cited by 4
3 results
People
The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial
Wu et al. 2013 · Critical care (London, England) · 361 people · cited by 105
4 results
People
A randomized, placebo-controlled trial of thymosin-alpha1 and lymphoblastoid interferon for HBeAg-positive chronic hepatitis B
Lim et al. 2006 · Antiviral therapy · 98 people · cited by 14
5 results

All 615 Thymosin alpha-1 studies

Thymosin alpha-1 clinical trials

ClinicalTrials.gov lists 56 trials of thymosin alpha-1. 13 are active or planned, and 2 have posted results. PepBank does not show trial results.

Solid bars are dates that happened. Hatched bars are planned dates. Data from ClinicalTrials.gov.

Experimental Trial of rhIFNα Nasal Drops to Prevent 2019-nCOV in Medical Staff

Phase 3status unknown2,944 planned

Thymosin-alpha 1 for Adjuvant Treatment After Radical Resection of High-risk Stage II and III Colorectal Cancer

Phase 3recruiting2,500 planned

The Efficacy and Safety of Ta1 for Sepsis

Phase 3completed1,106 people

All 19 Thymosin alpha-1 trials

Status and safety

Is thymosin alpha-1 approved?

FDA

United States

Not approved

No approved medicine contains it.

EMA

European Union

Not approved

No approved medicine contains it.

WADA

Sport

Not banned

Not on the 2026 Prohibited List.

Yes. Approved outside the US and EU (Singapore, China, Philippines). No FDA approval and no central EU authorisation (EMA). Not listed as banned by WADA.

Laws and labels change, so check the regulator for the current status.

Thymosin alpha-1 side effects and safety

PepBank has 54 safety results from studies of thymosin alpha-1. 45 of them come from studies in people.

Safety results from studies (54)

In people with hepatitis B cirrhosis, both thymosin α1 plus entecavir and entecavir alone were reported to be well tolerated. (Expert opinion on biological therapy, 2018)
In hepatitis C patients, thymosin alpha‑1 and placebo groups had no significant difference in side effects. (Journal of viral hepatitis, 2012)
In people with severe acute pancreatitis, new organ failure was not different with thymosin α1 than with placebo. (Intensive care medicine, 2022)
In ICU patients with severe sepsis, no serious side effect linked to thymosin alpha‑1 was recorded. (Critical care, 2013)
In Japanese adults with chronic hepatitis B given thymosin alpha‑1, all adverse drug reactions were mild and most involved changes in liver enzyme levels. (Journal of viral hepatitis, 2005)
In dialysis patients, fewer deaths were counted with thymalfasin (3) than in the control group (7), without a statistical test. (International immunopharmacology, 2023)
In people with tuberculosis and diabetes, adding thymosin alpha‑1 to chemotherapy did not change how often adverse reactions happened. (Pakistan journal of medical sciences, 2022)
In people with chronic hepatitis B, no significant side effects were seen with thymosin alpha1. (Hepatology, 1998)
In elderly men given influenza vaccine, no toxicity was seen with thymosin alpha‑1 or with placebo. (Journal of the American Geriatrics Society, 1989)
In adults with septic shock, adding thymosin alpha‑1 to blood purification did not change how often adverse events happened. (Alternative therapies in health and medicine, 2022)
In HBeAg-positive chronic hepatitis B, adding thymosin alpha‑1 to peginterferon did not significantly change the rate of side effects. (Scandinavian journal of gastroenterology, 2012)
In people with chronic hepatitis B, thymosin-alpha1 treatment caused no side effects. (Digestive diseases and sciences, 2000)
In people with chronic hepatitis B, thymosin-alpha1 was well tolerated by all patients, unlike interferon. (Hepatology, 1996)
In adults with chronic hepatitis B, all patients given thymosin alpha‑1 tolerated it well and none reported side effects. (World journal of gastroenterology, 2006)
In adults with liver cancer, the same number of patients had serious side effects with thymalfasin plus TACE as with TACE alone. (Hepatology international, 2009)
In adults with HIV and low CD4 counts on treatment, thymosin alpha‑1 was well tolerated, with no serious adverse events. (Clinical and experimental immunology, 2003)
In people with chronic hepatitis C, thymosin alpha‑1 caused no reported side effects except discomfort at the injection site in some patients. (Liver, 1996)
In transplant patients with infection, thymosin α1 did not cause graft versus host disease. (International journal of hematology, 2013)
In metastatic melanoma, adding thymosin alpha‑1 to dacarbazine and interferon alfa did not cause extra toxicity. (Journal of clinical oncology, 2010)
In hospitalized COVID-19 patients, nine serious adverse events in the thymalfasin group were judged not related to the treatment. (The Journal of infectious diseases, 2023)
In people with chronic hepatitis B, thymosin-α1 may lead to fewer serious side effects than control, based on low-certainty evidence. (The Cochrane database of systematic reviews, 2026)
In people with hepatitis B cirrhosis, adding thymosin α1 to entecavir led to fewer adverse events than entecavir alone. (BMC gastroenterology, 2020)
In people with gastric cancer, adding thymosin α1 to chemotherapy was linked to fewer gut side effects in pooled trials. (Frontiers in immunology, 2026)
In dialysis patients, no side effect was linked to thymosin α1 or to the flu vaccine. (Vaccine, 2012)

See every safety result on the Scientific page

Doses studied (40 shown)

The doses that these studies used. They are not recommendations.

Dose as reported	Class	Species	Route	Duration	Design	Source
1.6 mg every 12 h for 7 days, then 1.6 mg once a day for 7 days	Human	human	subcutaneous	14 days	Randomized trial in people · n = 508	Ke 2022
1.6 mg every 12 h for the first 7 days, then 1.6 mg once a day for 7 days	Human	human	subcutaneous	14 days	Randomized trial in people · n = 290	Ke 2023
1.6 microg three times per week	Human	human	Not reported	24 weeks	Randomized trial in people · n = 98	Lim 2006
3.2 mg	Human	human	Not reported	Not reported	Randomized trial in people	Maio 2010
1.6-6.4 mg	Human	human	Not reported	Not reported	Randomized trial in people	Maio 2010
1.6 mg twice weekly	Human	human	subcutaneous	48 weeks	Randomized trial in people · n = 552	Ciancio 2012
0.8 mg	Human	human	Not reported	24 weeks	Randomized trial in people · n = 316	Iino 2005
0.8 mg or 1.6 mg	Human	human	Not reported	24 weeks	Randomized trial in people · n = 316	Iino 2005
0.8 mg and 1.6 mg	Human	human	Not reported	24 weeks	Randomized trial in people · n = 316	Iino 2005
1.6 mg twice weekly	Human	human	subcutaneous	8 weeks	Randomized trial in people · n = 194	Tuthill 2023
1.6 mg twice weekly	Human	human	subcutaneous	26 weeks	Randomized trial in people · n = 109	Sherman 1998
1.6 mg twice weekly	Human	human	subcutaneous	26 or 52 weeks	Randomized trial in people · n = 98	Chien 1998
1.6 mg two times a week	Human	human	Not reported	26 or 52 weeks	Randomized trial in people · n = 98	Chien 2006
1.6 mg twice weekly	Human	human	Not reported	6 months	Randomized trial in people · n = 97	Mutchnick 1999
900 micrograms/m2 twice weekly	Human	human	subcutaneous	eight doses	Randomized trial in people · n = 90	Gravenstein 1989
1.6 mg	Human	human	hypodermic injection	10 injections, every other day	Randomized trial in people · n = 80	Zheng 2008
1.6 mg twice a week	Human	human	subcutaneous	24 weeks	Randomized trial in people · n = 67	Lee 2008
1.6 mg twice a week	Human	human	subcutaneous	6 months	Randomized trial in people · n = 62	You 2006
1.6 mg once daily	Human	human	subcutaneous injection	7 days	Randomized trial in people · n = 52	Zhang 2015
1.6 mg twice a week	Human	human	Not reported	12 weeks	Randomized trial in people · n = 51	Kim 2012
1.6 mg	Human	human	subcutaneous	7 days	Randomized trial in people · n = 47	Li 2009
1.6 mg	Human	human	subcutaneous	7 days	Randomized trial in people · n = 47	Zhou 2009
900 microg/m2 twice a week	Human	human	Not reported	six months	Randomized trial in people · n = 44	Zavaglia 2000
1.6 mg twice daily	Human	human	subcutaneous	1 week	Randomized trial in people · n = 42	Chen 2007
11.6 mg daily	Human	human	subcutaneous	7 days	Randomized trial in people · n = 42	Huang 2006
900 microg/m2 body surface area	Human	human	Not reported	6 months	Randomized trial in people · n = 41	Andreone 2004
1 mg twice weekly	Human	human	Not reported	6 months	Randomized trial in people · n = 34	Moscarella 1998
900 microg/m2 twice weekly	Human	human	Not reported	6 months	Randomized trial in people · n = 33	Andreone 1996
1.6 mg, 5 times weekly	Human	human	subcutaneous	24 weeks	Randomized trial in people · n = 25	Gish 2009
1.6 mg or 3.2 mg	Human	human	Not reported	52 weeks	Randomized trial in people · n = 25	Jiang 2010
3.2 mg	Human	human	Not reported	52 weeks	Randomized trial in people · n = 25	Jiang 2010
3.2 mg twice weekly	Human	human	subcutaneous	12 weeks	Randomized trial in people · n = 20	Chadwick 2003
900 micrograms/m2 twice weekly	Human	human	Not reported	six months	Randomized trial in people · n = 19	Andreone 1996
0.8 mg or 1.6 mg	Human	human	Not reported	two weeks six times weekly, then 22 weeks twice weekly	Randomized trial in people · n = 16	Arase 2003
900 µg/m2	Human	human	subcutaneous	single dose and 5 days	Randomized trial in people · n = 9	Rost 1999
1.6 mg	Human	human	Not reported	24 weeks	Randomized trial in people	Iino 2005
1.6 mg once a day in week 1, then twice a week from week 2 to week 12	Human	human	subcutaneous	12 weeks	Randomized trial in people	Chen 2022
1.6 mg once per day	Human	human	subdermal injection	6 days	Randomized trial in people	Xiao 2015
1.6 mg twice a week	Human	human	Not reported	Not reported	Randomized trial in people	Niu 2024
1.6 mg thrice a week	Human	human	Not reported	Not reported	Randomized trial in people	Niu 2024

From the community

How people use it

What people report online. It comes from forums and guides, not from studies.

Community-reported. Not tested in trials.

Thymosin alpha-1 is an approved drug (Zadaxin) in some countries for chronic hepatitis B and C. Community sources report off-label use for general immune support at the label amount (about 1.5 to 1.6 mg twice a week), with a lower daily plan and some higher-amount plans.

Reported routines and cautions

What people use it for

General immune support and illness prevention (off-label)S2S3
Lyme disease co-treatment, chronic fatigue and mold illness protocols (off-label, community claims)S2
Chronic hepatitis B and C (approved use in some countries, with a prescriber)S1

Reported regimens

Regimens that community sources report for Thymosin alpha-1. Community-reported, not tested in trials.
Context	Route	Amount	How often	How long	Agreement	Sources
Chronic hepatitis B (label, Singapore register for Zadaxin)Official label dosing of an approved product	subcutaneous injectionalone or with interferon; patients under 40 kg get 40 mcg/kg	1.6 mg per dose	twice a week	6 to 12 months	single source (official label)	S1
General immune support (standard protocol)	subcutaneous injection	1.5 to 1.6 mg per dose	twice weekly	8 to 12 weeks	2 sources agree on about 1.5 to 1.6 mg twice weekly; S3 reports some higher community amounts. Both sources carry seller links.	S2S3
Daily low-dose plan for gradual immune support	subcutaneous injection	300 to 500 mcg per dose	once daily	4 to 8 weeks	single source. The source carries seller links.	S2
Acute illness (front-loading, then twice weekly)	subcutaneous injection	1.6 mg per dose	daily for 3 to 5 days, then twice weekly (S3: daily)	2 to 4 weeks (S3: 7 to 14 days)	sources differ: amount agrees (1.6 mg); S2 says daily for 3 to 5 days then twice weekly for 2 to 4 weeks, S3 says daily for 7 to 14 days. Both sources carry seller links.	S2S3

Reported side effects

generally very well tolerated; occasional mild injection-site reactions and brief tirednessS2
a short rise in liver enzyme ALT can occur during treatment for hepatitis B (label)S1

Reported benefits (claims, not shown in trials)

fewer colds, better energy and symptom control during infection (self-reported)S2

Cautions

Community outcomes are self-reported, without controls, blinding or objective measurement.S2
The safety record in clinical use does not validate off-label uses. Immune support in healthy people was not the focus of clinical trials.S2S3
The label says Zadaxin is contraindicated after hypersensitivity to thymosin alpha 1 and should be considered contraindicated in people who are deliberately immunosuppressed, such as organ transplant patients.S1
Product quality varies between compounding pharmacies and research chemical suppliers.S2

Status notes

Zadaxin is a prescription medicine for hepatitis B and C in places such as Singapore. The FDA page current as of 2026-04-22 lists thymosin-alpha 1 among compounding substances that were in Category 2 and whose nominations were withdrawn.S1 S4

Community sources

S1ZADAXIN INJECTION [SIN07483P] product information (opens in a new tab)ndf.gov.sg
S2Thymosin Alpha-1: Community Protocols & Reportspeptideprotocolwiki.comcarries seller links, not linked
S3Thymosin Alpha-1outliyr.comcarries seller links, not linked
S4Certain bulk drug substances for use in compounding that may present significant safety risks (opens in a new tab)fda.gov

Gaps

Only one non-seller community source (S2) gives amounts, and S3 carries affiliate or shop links, so it is marked seller-linked. No forum threads were readable (Reddit is blocked). The label is from Singapore; no US FDA label exists to check, and no EMA label was found. The long-term maintenance plan in S2 (1.5 mg once weekly, 3 months on and 1 month off) was left out for space. No harm-reduction source was found.

Questions and more

Common questions

What benefits do studies report for thymosin alpha-1?

Results are mixed.^4,23 In a randomized trial of people with hepatitis B liver failure, 90-day transplant-free survival was 75.0% with thymosin alpha-1 and 53.4% with standard care alone.²³ In a randomized trial of 52 ventilated patients, ICU stay and time on the ventilator were shorter with thymosin alpha-1 than with routine care.²⁴ See what thymosin alpha-1 studies show

Is thymosin alpha-1 the same as Zadaxin?

Yes.¹ Zadaxin is the SciClone Pharmaceuticals brand for thymalfasin, the name used for thymosin alpha-1 made by synthesis.^1,5 Zadaxin was approved for chronic hepatitis B in Singapore in 1993, in China in 1996 and in the Philippines by 1997.^1,10,11,25 The FDA and EMA have not approved it.^6,7 See if thymosin alpha-1 is approved

Is thymosin alpha-1 safe?

It is not known what risks compounded thymosin alpha-1 carries, because the FDA calls the safety information inadequate.⁶ The FDA also says compounded thymosin alpha-1 may carry a significant risk of immune reactions for certain routes of administration.⁶ In a trial of 361 patients with severe sepsis, no serious drug-related adverse event was recorded with thymosin alpha-1.² See thymosin alpha-1 side effects and safety

What results did people see in thymosin alpha-1 studies?

In people with predicted severe acute necrotizing pancreatitis, infected pancreatic necrosis occurred in 15.7% with thymosin alpha-1 and 18.1% with placebo, a non-significant difference.⁴ In a retrospective study of people with mild COVID-19, progression to severe disease was 2.17% with thymosin alpha-1 and 2.71% with standard care alone, which did not differ.²⁶ See the key thymosin alpha-1 studies

Ask a question about thymosin alpha-1

The answer links to every study it uses.

What does the evidence say about thymosin alpha-1?Is thymosin alpha-1 tested in people?Compare with Vasoactive intestinal peptide (VIP, aviptadil)Compare with Thymalin

Sources

Database: PepBank profile: identity and structure (GSRS THYMALFASIN (UNII W0B22ISQ1C); UniProt P06454 (PTMA_HUMAN); PubChem CID 16130571)
People: Wu et al., 2013, Critical care (London, England) (PMID 23327199)
People: Wu et al., 2018, Expert opinion on biological therapy (PMID 30063860)
People: Ke et al., 2022, Intensive care medicine (PMID 35713670)
Database: Development record
Regulator: FDA (United States) status record, as of 2026-10-08
Regulator: EMA (European Union) status record, as of 2026-10-08
Regulator: WADA Prohibited List 2026
Database: PepBank data for Thymosin alpha-1 (data version 308541)
Regulator: Other regulator or record: Singapore
Regulator: Other regulator or record: China
Trial registry: ClinicalTrials.gov NCT02867267: The Efficacy and Safety of Ta1 for Sepsis
Database: Target record: Toll-like receptor 9 (TLR9)
People: Wu et al., 2022, Pakistan journal of medical sciences (PMID 35035422)
People: Ciancio et al., 2012, Journal of viral hepatitis (PMID 22233415)
People: Bai et al., 2022, Alternative therapies in health and medicine (PMID 35951068)
People: Sherman et al., 1998, Hepatology (Baltimore, Md.) (PMID 09537454)
People: Lim et al., 2006, Antiviral therapy (PMID 16640105)
People: Shuqun et al., 2004, Hepato-gastroenterology (PMID 15362772)
People: Maio et al., 2010, Journal of clinical oncology (PMID 20194853)
People: Jia et al., 2015, Immunopharmacology and immunotoxicology (PMID 26250523)
People: Zheng et al., 2008, Sichuan da xue xue bao. Yi xue ban = Journal of Sichuan University. Medical science edition (PMID 18798500)
People: Chen et al., 2022, Hepatology international (PMID 35616850)
People: Zhang et al., 2015, Sichuan da xue xue bao. Yi xue ban = Journal of Sichuan University. Medical science edition (PMID 26867337)
Regulator: Other regulator or record: Philippines
People: Huang et al., 2021, Frontiers in medicine (PMID 33968969)

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Thymosin alpha-1

Approved in Singapore, China +1Not banned in sport

Also known as Ta1, Tα1, Thymosin alpha 1, Thymosin alpha1, alpha1-Thymosin, Thymalfasin and 1 more

What it is

Natural fragment, 28 amino acids

Approval

Approved outside the US and EU (Singapore, China, Philippines)

In sport

Not listed as banned by WADA

Studies

615 studies with results. 332 of them gave thymosin alpha-1, with 1,450 results.
603 in people380 in animals462 in lab cells5 from computer models

Best study in people

Randomized controlled trial with 690 people (2018)

Clinical trials

56 registered: 13 active or planned, 2 with posted results

Community use

General immune support and illness prevention (off-label); Lyme disease co-treatment, chronic fatigue and mold illness protocols (off-label, community claims); Chronic hepatitis B and C (approved use in some countries, with a prescriber)

Dose as reported

Class

Species

Route

Duration

Design

Source

1.6 mg every 12 h for 7 days, then 1.6 mg once a day for 7 days

Human

human

subcutaneous

14 days

Randomized trial in people · n = 508

Ke 2022

1.6 mg every 12 h for the first 7 days, then 1.6 mg once a day for 7 days

Human

human

subcutaneous

14 days

Randomized trial in people · n = 290

Ke 2023

1.6 microg three times per week

Human

human

Not reported

24 weeks

Randomized trial in people · n = 98

Lim 2006

3.2 mg

Human

human

Not reported

Randomized trial in people

Maio 2010

1.6-6.4 mg

Human

human

Not reported

Randomized trial in people

Maio 2010

1.6 mg twice weekly

Human

human

subcutaneous

48 weeks

Randomized trial in people · n = 552

Ciancio 2012

0.8 mg

Human

human

Not reported

24 weeks

Randomized trial in people · n = 316

Iino 2005

0.8 mg or 1.6 mg

Human

human

Not reported

24 weeks

Randomized trial in people · n = 316

Iino 2005

0.8 mg and 1.6 mg

Human

human

Not reported

24 weeks

Randomized trial in people · n = 316

Iino 2005

1.6 mg twice weekly

Human

human

subcutaneous

8 weeks

Randomized trial in people · n = 194

Tuthill 2023

1.6 mg twice weekly

Human

human

subcutaneous

26 weeks

Randomized trial in people · n = 109

Sherman 1998

1.6 mg twice weekly

Human

human

subcutaneous

26 or 52 weeks

Randomized trial in people · n = 98

Chien 1998

1.6 mg two times a week

Human

human

Not reported

26 or 52 weeks

Randomized trial in people · n = 98

Chien 2006

1.6 mg twice weekly

Human

human

Not reported

6 months

Randomized trial in people · n = 97

Mutchnick 1999

900 micrograms/m2 twice weekly

Human

human

subcutaneous

eight doses

Randomized trial in people · n = 90

Gravenstein 1989

1.6 mg

Human

human

hypodermic injection

10 injections, every other day

Randomized trial in people · n = 80

Zheng 2008

1.6 mg twice a week

Human

human

subcutaneous

24 weeks

Randomized trial in people · n = 67

Lee 2008

1.6 mg twice a week

Human

human

subcutaneous

6 months

Randomized trial in people · n = 62

You 2006

1.6 mg once daily

Human

human

subcutaneous injection

7 days

Randomized trial in people · n = 52

Zhang 2015

1.6 mg twice a week

Human

human

Not reported

12 weeks

Randomized trial in people · n = 51

Kim 2012

1.6 mg

Human

human

subcutaneous

7 days

Randomized trial in people · n = 47

Li 2009

1.6 mg

Human

human

subcutaneous

7 days

Randomized trial in people · n = 47

Zhou 2009

900 microg/m2 twice a week

Human

human

Not reported

six months

Randomized trial in people · n = 44

Zavaglia 2000

1.6 mg twice daily

Human

human

subcutaneous

1 week

Randomized trial in people · n = 42

Chen 2007

11.6 mg daily

Human

human

subcutaneous

7 days

Randomized trial in people · n = 42

Huang 2006

900 microg/m2 body surface area

Human

human

Not reported

6 months

Randomized trial in people · n = 41

Andreone 2004

1 mg twice weekly

Human

human

Not reported

6 months

Randomized trial in people · n = 34

Moscarella 1998

900 microg/m2 twice weekly

Human

human

Not reported

6 months

Randomized trial in people · n = 33

Andreone 1996

1.6 mg, 5 times weekly

Human

human

subcutaneous

24 weeks

Randomized trial in people · n = 25

Gish 2009

1.6 mg or 3.2 mg

Human

human

Not reported

52 weeks

Randomized trial in people · n = 25

Jiang 2010

3.2 mg

Human

human

Not reported

52 weeks

Randomized trial in people · n = 25

Jiang 2010

3.2 mg twice weekly

Human

human

subcutaneous

12 weeks

Randomized trial in people · n = 20

Chadwick 2003

900 micrograms/m2 twice weekly

Human

human

Not reported

six months

Randomized trial in people · n = 19

Andreone 1996

0.8 mg or 1.6 mg

Human

human

Not reported

two weeks six times weekly, then 22 weeks twice weekly

Randomized trial in people · n = 16

Arase 2003

900 µg/m2

Human

human

subcutaneous

single dose and 5 days

Randomized trial in people · n = 9

Rost 1999

1.6 mg

Human

human

Not reported

24 weeks

Randomized trial in people

Iino 2005

1.6 mg once a day in week 1, then twice a week from week 2 to week 12

Human

human

subcutaneous

12 weeks

Randomized trial in people

Chen 2022

1.6 mg once per day

Human

human

subdermal injection

6 days

Randomized trial in people

Xiao 2015

1.6 mg twice a week

Human

human

Not reported

Randomized trial in people

Niu 2024

1.6 mg thrice a week

Human

human

Not reported

Randomized trial in people

Niu 2024

Context

Route

Amount

How often

How long

Agreement

Sources

Chronic hepatitis B (label, Singapore register for Zadaxin)Official label dosing of an approved product

subcutaneous injectionalone or with interferon; patients under 40 kg get 40 mcg/kg

1.6 mg per dose

twice a week

6 to 12 months

single source (official label)

General immune support (standard protocol)

subcutaneous injection

1.5 to 1.6 mg per dose

twice weekly

8 to 12 weeks

2 sources agree on about 1.5 to 1.6 mg twice weekly; S3 reports some higher community amounts. Both sources carry seller links.

S2S3

Daily low-dose plan for gradual immune support

subcutaneous injection

300 to 500 mcg per dose

once daily

4 to 8 weeks

single source. The source carries seller links.

Acute illness (front-loading, then twice weekly)

subcutaneous injection

1.6 mg per dose

daily for 3 to 5 days, then twice weekly (S3: daily)

2 to 4 weeks (S3: 7 to 14 days)

sources differ: amount agrees (1.6 mg); S2 says daily for 3 to 5 days then twice weekly for 2 to 4 weeks, S3 says daily for 7 to 14 days. Both sources carry seller links.

S2S3

Thymosin alpha-1

Key points

Thymosin alpha-1 at a glance

What is thymosin alpha-1?

The history of thymosin alpha-1

Thymosin alpha-1 structure and chemistry

How does thymosin alpha-1 work?

What thymosin alpha-1 studies show

Immune system and inflammation

Infections

Survival and serious illness

Liver

Cancer

Lungs and breathing

Key thymosin alpha-1 studies

Thymosin alpha-1 clinical trials

Is thymosin alpha-1 approved?

Thymosin alpha-1 side effects and safety

How people use it

What people use it for

Reported regimens

Reported side effects

Reported benefits (claims, not shown in trials)

Cautions

Status notes

Community sources

Common questions

What benefits do studies report for thymosin alpha-1?

Is thymosin alpha-1 the same as Zadaxin?

Is thymosin alpha-1 safe?

What results did people see in thymosin alpha-1 studies?

Ask a question about thymosin alpha-1

Related peptides

Sources

Thymosin alpha-1

Key points

Thymosin alpha-1 at a glance

What is thymosin alpha-1?

The history of thymosin alpha-1

Thymosin alpha-1 structure and chemistry

How does thymosin alpha-1 work?

What thymosin alpha-1 studies show

Immune system and inflammation

Infections

Survival and serious illness

Liver

Cancer

Lungs and breathing

Key thymosin alpha-1 studies

Thymosin alpha-1 clinical trials

Is thymosin alpha-1 approved?

Thymosin alpha-1 side effects and safety

How people use it

What people use it for

Reported regimens

Reported side effects

Reported benefits (claims, not shown in trials)

Cautions

Status notes

Community sources

Common questions

What benefits do studies report for thymosin alpha-1?

Is thymosin alpha-1 the same as Zadaxin?

Is thymosin alpha-1 safe?

What results did people see in thymosin alpha-1 studies?

Ask a question about thymosin alpha-1

Related peptides

Sources