Peptide dossier, updated Nov 1, 2026

Thymosin alpha-1

A synthetic version of a thymus-derived peptide, also called thymalfasin. SciClone, the company that markets it as ZADAXIN, says in its 10-K that it is approved in over 30 countries. FDA has not approved it, and lists it as a compounding substance that may pose safety risks. It is the most studied of this batch, with several randomized trials whose results are mixed. This page lays out what each source actually says.

See all 11 verified records for Thymosin alpha-1 on the Records page

In plain terms

Approved for: Nothing from FDA, and we found no application in openFDA’s data. Abroad, SciClone’s 2015 annual report says its product ZADAXIN (thymalfasin) is approved in over 30 countries, principally for hepatitis B and as an immune system enhancer, with China about 96% of sales. That is the company’s statement; we did not check each country.

What it is: A synthetic version of a peptide that comes from the thymus gland. A 2010 trial paper describes it as an immunomodulatory polypeptide that enhances effector T-cell responses.

What it is said to do, and by whom:

The 2009 review: calls it the first of the thymosins in clinical use, and reports applications in hepatitis, as an immune stimulant, and in sepsis, lung infections and chemotherapy support.
Researchers: a 2013 sepsis trial in China (361 patients) reported 28-day mortality of 26.0% versus 35.0% with a marginal p-value. A 2010 melanoma trial (488 patients) reported tumor responses in the thymosin arms and concluded it had activity.
Researchers: a 2022 double-blind trial in 508 patients with severe pancreatitis found it did not reduce infected necrosis.

How strong the evidence is: Mixed, and the strongest in this batch. There are several randomized trials, mostly in hospitalized or cancer patients, with some positive signals, some marginal and some negative. None tests the wellness uses sellers promote, and two registered trials list SciClone Pharmaceuticals, its marketer, as sponsor.

FDA safety-risk page

Listed

FDA says compounded drugs containing it may pose significant immunogenicity risk, and that safety information is inadequate to understand the extent of any safety issues.

Approval abroad

Over 30 countries, per the company

SciClone’s 10-K for 2015 says ZADAXIN is approved in over 30 countries. We did not check each country. No FDA application appears in openFDA’s data.

HHS enforcement, Oct 30

Not covered

The draft policy’s covered list names six peptides: BPC-157, epitalon, KPV, MOTS-c, Semax and TB-500. Thymosin alpha-1 is not one of them. Draft policy. Not binding.

FDA advisory panel, July

Not reviewed

FDA’s Federal Register notice for the July 23–24 meeting lists seven peptides. Thymosin alpha-1 is not among them.

WADA prohibited list

Not named

We did not find it in the 2026 list. We read a copy hosted by an athletics federation, and checked only the 2026 edition.

Human evidence

Several randomized trials, mixed

ClinicalTrials.gov lists 66 studies. Published randomized trials are in sepsis, pancreatitis, melanoma and hepatitis, with mixed results.

Human studies

ClinicalTrials.gov lists 66 studies for thymosin alpha-1 or thymalfasin as of Nov 1, 2026. Selected phase 2 to 3 records are below. None of these shows posted results.

Registry	Study	Sponsor	Status
NCT00039962	Phase 3: thymosin plus peginterferon in hepatitis C patients with cirrhosis who did not respond to treatment	SciClone Pharmaceuticals	Completed
NCT01178996	Phase 3: thymosin alpha-1 with peginterferon alfa-2a and ribavirin	sigma-tau	Completed
NCT04487444	Phase 2: thymalfasin for COVID-19 infection	Rhode Island Hospital	Terminated
NCT06584006	Phase 2: thymalfasin with recombinant IL-2 for lymphocytopenia	First Affiliated Hospital of Xiamen University	Recruiting

Registry entries are written by sponsors and are not reviewed for scientific merit. A registered study is not a result. We did not open each record.

FDA review

FDA’s safety-risk page (content current Apr 22, 2026) is the one FDA document on thymosin alpha-1 that we read.

What the page says

It lists “Thymosin-alpha 1 (Ta1)” in the table of bulk drug substances nominated but withdrawn, previously in category 2 under the interim policies.
It says compounded drugs containing it may pose significant risk for immunogenicity for certain routes and may have complexities with peptide-related impurities and API characterization.
It says the safety-related information is inadequate for the agency to sufficiently understand the extent of any safety issues raised by the proposed compounded drug.

What we did not find

We found no FDA briefing document, advisory committee review or press release specific to thymosin alpha-1.
We found no FDA warning letter naming it. Absence is not proven.

Sources: FDA: bulk substances that may present significant safety risks

Published research

PubMed returns 581 results for “thymosin alpha 1” and 59 for “thymalfasin” in the title or abstract as of Nov 1, 2026. We read the abstracts of four randomized trials.

What the trials show

Severe sepsis, 2013. 361 patients in six Chinese hospitals, single-blind. 28-day mortality was 26.0% with thymosin versus 35.0% in controls (p = 0.062 non-stratified, 0.049 by log rank). The authors report no serious drug-related adverse event. Crit Care PubMed
Severe pancreatitis, 2022. 508 patients, double-blind and placebo-controlled. Infected pancreatic necrosis occurred in 15.7% with thymosin versus 18.1% with placebo (p = 0.48). The authors conclude it did not reduce infected necrosis. Intensive Care Med PubMed
Metastatic melanoma, 2010. 488 patients across five arms. Tumor responses were 10 and 12 in two thymosin arms versus 4 in the control arm. Survival differences were not statistically significant (p = .08). J Clin Oncol PubMed
Review, 2009. Describes approvals in over 35 countries and the range of clinical uses. Expert Opin Biol Ther PubMed
Company filing, 2016. SciClone’s 10-K for 2015 says ZADAXIN is approved in over 30 countries, principally for hepatitis B and as an immune system enhancer, that China was about 96% of its sales, and that worldwide sales passed $146 million. SEC EDGAR SEC filing

Read with care

The sepsis result sits at the edge of conventional significance, and the trial was single-blind.
Two registry records list SciClone Pharmaceuticals, the company that markets it as ZADAXIN, as sponsor. We did not check the sponsorship of each paper.
We read abstracts only, not full text, funding or disclosures.

Timeline

Newest first. Every entry links to the document it comes from.

Government or registry record
Journal

Oct 30, 2026Regulatory
HHS publishes draft policy pausing enforcement on six peptides; Thymosin alpha-1 is not one of them
The draft policy’s appendix names six peptides: BPC-157, epitalon, KPV, MOTS-c, Semax and TB-500. The policy is a draft and not FDA approval. We read the appendix through a text extraction.
Federal Register Docket HHS policy appendix BakerHostetler summary
July 23–24, 2026Regulatory
FDA advisory committee meets on seven peptides; Thymosin alpha-1 is not among them
The committee recommended six of the seven, all nonbinding. FDA’s notice of the meeting does not list Thymosin alpha-1.
Federal Register notice Holland & Knight summary
Apr 22, 2026Regulatory
FDA’s safety-risk page lists Thymosin alpha-1
FDA lists thymosin alpha-1 as nominated-but-withdrawn and says the safety-related information is inadequate.
FDA page
2022Literature
Double-blind trial in severe pancreatitis: no reduction in infected necrosis
508 patients. Published in Intensive Care Med.
PubMed
Mar 11, 2016SEC filing
SciClone 10-K says ZADAXIN is approved in over 30 countries
The company reports China at about 96% of sales and worldwide sales above $146 million for 2015.
SEC EDGAR
2013Literature
Sepsis trial reports 28-day mortality of 26.0% versus 35.0%
361 patients, p = 0.062 non-stratified. Published in Crit Care.
PubMed
2010Literature
Melanoma trial of thymosin alpha-1 with dacarbazine and interferon
488 patients. Published in J Clin Oncol.
PubMed

Still not covered

Left off rather than guessed:

HHS policy: we read the draft policy appendix through a text extraction, not as the original PDF layout. It names six covered peptides and not thymosin alpha-1.
FDA review: we found no FDA briefing document or advisory committee evaluation for thymosin alpha-1. FDA’s notice for the July meeting does not name it, so the safety-risk page entry is the only FDA statement on it that we read.
Approvals abroad: the company’s 2015 10-K and a 2009 review give different counts (over 30 and over 35). We did not find a regulator’s own record, and the 10-K is the company speaking about its own product.
Trials and sponsors: we did not open every registry record or check who funded each trial.
Drugs@FDA: we searched openFDA’s copy of the Drugs@FDA data by active ingredient and found no application. FDA’s own Drugs@FDA site could not be searched from our tools.
Patents and SEC filings: not researched for this dossier.
Seller claims and independent lab reports: how gray-market product is marketed versus what testing finds. We have not collected testing data.
Unread items: full text of most papers; EU and other non-US regulators and registries; WADA lists for years other than 2026; FDA warning letters beyond those listed, which rest on web searches.