Is Thymosin Alpha 1 FDA Approved? The Full Record

Is thymosin alpha 1 FDA approved? It isn't, and it never has been: no thymosin alpha-1 product has ever been FDA-approved in the United States. Overseas it's a different story. Its drug form, thymalfasin, sold as Zadaxin, is licensed in dozens of countries, according to its maker, mostly for hepatitis B. Here it collected four orphan-drug designations and several late-stage trials, and none of that ended in approval.

A separate question is whether pharmacies may compound it. On December 4, 2024, FDA's outside advisers voted 4 to 17 against adding it to the federal list that decides that, and FDA hasn't turned the vote into a rule. The molecule and its trials have their own page: the thymosin alpha-1 trial record.

Is thymosin alpha 1 FDA approved? No: the record, date by date

Zadaxin: licensed abroad, never approved in the U.S.

Thymosin alpha-1 was pulled out of calf thymus and sequenced in 1977 (Goldstein et al., PNAS). Thymalfasin is its drug name, and Zadaxin is the brand SciClone Pharmaceuticals built around it.

SciClone's annual report for 2007 said that, besides China, Zadaxin was "approved in over 34 countries, primarily in Asia, the Middle East and Latin America," mainly for hepatitis B (SciClone Form 10-K). FDA's reviewers wrote in 2024 that the agency was "unable to independently verify" claims like these.

At home, FDA's orphan-drug database lists four designations: chronic active hepatitis B in 1991, DiGeorge anomaly in 1998, liver cancer in 2000 and advanced melanoma in 2006. An orphan designation is a package of incentives for developing a rare-disease drug, not an approval, and all four entries still read "Not FDA Approved for Orphan Indication."

The trials didn't deliver. A phase 3 trial led from Wayne State University in Detroit gave 97 people with chronic hepatitis B the peptide or a placebo: complete response came to 14% versus 4%, short of statistical significance (P=0.084). The authors wrote that their results "do not confirm observations of treatment efficacy reported in other clinical studies" (Mutchnick et al., Journal of Viral Hepatitis 1999). Two phase 3 hepatitis C trials, completed in 2005 and 2006, also missed statistical significance, the company reported.

The 503A nomination and Category 2

Compounding means a pharmacy preparing a medicine for one patient's prescription. Under Section 503A of federal drug law, a pharmacy can start from a raw ingredient only if it has an official USP monograph (a published quality standard), is part of an approved drug, or sits on the 503A bulks list. Thymosin alpha-1 has no monograph and is not a component of any FDA-approved drug, so the list is its only route.

Wells Pharmacy Network sent in the nomination, logged on February 9, 2021. In a document marked "Updated September 29, 2023," preserved by the Alliance for Pharmacy Compounding, FDA placed it in Category 2, its group for nominated ingredients that raise significant safety concerns. FDA's safety summary says compounded thymosin alpha-1 "may pose significant risk for immunogenicity," meaning the immune system could react to the drug itself.

The withdrawal reached the docket on September 18, 2024. FDA's update dated September 27, 2024 removed it from Category 2 "because the nomination was withdrawn" and, in the same entry, announced a committee review. That wasn't a step toward approval: FDA kept evaluating it on its own initiative.

What FDA's staff review found

FDA's briefing document, dated November 15, 2024, covered two forms, the free base and the acetate salt, since the nomination hadn't made clear which it meant. Staff looked at 12 uses, including hepatitis B and C, melanoma, sepsis and COVID-19; five of them FDA added on its own.

• Identity and purity. Data on impurities, clumping and bacterial toxins were missing, so neither form was "well-characterized."
• Safety. Most trials found it well tolerated, with irritation or redness at the injection site the most common reaction. The concern was the compounded injection, which "may pose a significant risk for immunogenicity."
• Effectiveness. Staff found "a lack of evidence to support the effectiveness" for all 12 uses, and noted that approved treatments exist for most of them.

The conclusion took one line: "we propose not adding Ta1 (free base) or Ta1 acetate to the 503A Bulks List."

The December 2024 vote: 4 to 17

The Pharmacy Compounding Advisory Committee (PCAC) is an outside expert panel that advises FDA. It met on December 4, 2024; 21 members voted on thymosin alpha-1, 11 of them seated for this topic alone. Six public speakers, including clinicians, a compounding pharmacy and a peptide-medicine society, argued for keeping it available; one warned that leaving it off would push patients toward "online fake pharmacies."

The official minutes record 4 votes for listing the free base and 17 against, and the same split for the acetate. Several members who voted no found "no compelling evidence demonstrating clinical effectiveness and safety." In the transcript, Robin Bogner, PhD, voting yes, said, "in this case I fell toward access." Brian Lee, MD, voting no, said the data "has not met that bar."

What has happened since the vote

Six weeks later, a 1,106-patient sepsis trial called TESTS found "no clear evidence" that the peptide lowered deaths (Wu et al., BMJ 2025). In April 2026, FDA moved several other peptides out of Category 2 and scheduled new committee meetings, but thymosin alpha-1 wasn't among them. The July 23–24, 2026 meeting covered seven other peptide groups, and the agenda for the next one, due before the end of February 2027, doesn't list it.

As of September 23, 2026, the day this article was written, FDA had published no proposed or final rule on thymosin alpha-1; the Federal Register's last mention of it was the October 2024 meeting notice. The regulation itself, 21 CFR 216.23, names six substances pharmacies may use and four FDA has turned down, and thymosin alpha-1 is on neither list. FDA's category document marked "Updated May 14, 2026" puts it in no category, while its safety summary stays posted. ClinicalTrials.gov listed one recruiting U.S. study: a small phase 1 trial at Houston Methodist pairing it with COVID-19 boosters in adults 65 and older.

The next formal step, if FDA takes one, would be a proposed rule with a public comment period. There is no published deadline.

What it means if a provider prescribes it

None of this is a ruling on one person; the review asked whether an ingredient belongs on a federal list. Thymosin alpha-1 isn't a controlled substance: it doesn't appear on the DEA's controlled substances list dated August 27, 2026. A licensed provider may still prescribe a compounded formulation; that decision is between you and your doctor. Federal and state compounding rules still apply to the pharmacy that fills it.

At Promise, thymosin alpha-1 is dispensed as a compounded medication and is not FDA-approved. The visit happens online, a licensed provider reviews every request, and not everyone qualifies. That conversation draws on the same record FDA read, including what the trials found on side effects.

A vial bought from a website comes with no prescriber, no pharmacy of record and no one to call. A prescription names what was ordered, a licensed U.S. compounding pharmacy dispenses and labels it, and a clinician is there if something feels wrong.