Thymosin Alpha-1: Legal Status and What FDA Reviewed

Legal status of Thymosin alpha-1

Not allowed in compounding

Thymosin alpha-1 cannot be legally compounded ^[1]. An FDA advisory committee voted against it in December 2024 ^[2], and we found no new review scheduled ^[14].

FDA status

FDA placed it in Category 2 on Sept 29, 2023 ^[7]. FDA now lists it as "nominated but withdrawn," which is outside every category ^[3]. We could not confirm when the nomination was withdrawn. It was not one of the 12 peptides FDA removed from Category 2 in April 2026 ^[8]. It is not in Category 1 and is not on the 503A bulks list, so a 503A pharmacy may not lawfully compound it today ^[1]. FDA says it may pose a significant immunogenicity risk for some routes and that safety information is inadequate ^[3].

Advisory committee

On Dec 4, 2024, the committee voted 4 yes and 17 no on both the free base and acetate forms ^[2].

FDA-approved products

None. We found no FDA-approved drug that contains Thymosin alpha-1.

Sports (WADA)

Thymosin alpha-1 is not named on the 2026 list ^[6]. The list's S0 class covers substances with no approval by any government health authority for human use ^[6]. Whether that class covers Thymosin alpha-1 is a judgment call, so athletes should ask their anti-doping agency before use.

What happens next

We found no pending FDA review. It is not on the July 2026 agenda or the five-peptide list planned for before the end of February 2027 ^{[4] [14]}. A new nomination or another FDA action would be needed before a pharmacy could compound it ^[9].

Checked against FDA sources on Oct 24, 2026. We update this box when FDA acts. Report a change: [email protected].

Voted down 17 to 4

FDA brought thymosin alpha-1 before its compounding advisory committee in late 2024. On Dec 4, 2024, the committee voted 4 yes and 17 no on the free base and 4 yes and 17 no on the acetate ^[2]. Members who voted no on the free base said there was "no compelling evidence demonstrating clinical effectiveness and safety," and the majority voted against the acetate "due to the lack of convincing effectiveness data" ^[2].

It was a closer vote than for the other peptides that day. Some members who voted yes said it "should be accessible to patients as an option for use" ^[2]. The majority still said no.

The uses the committee reviewed

FDA's minutes list the proposed uses, among them ^[2]:

• Hepatitis B
• Hepatitis C
• HIV
• COVID-19
• Depressed response to vaccinations
• Sepsis and COPD, among several others

None of those uses led to a favorable vote. Online marketing for general immune support goes further than anything the committee considered. One telehealth seller, PeRx, lists thymosin alpha-1 on its menu ^[13]; we rate it Avoid.

Where it sits today

FDA put thymosin alpha-1 in Category 2 in September 2023 ^[7]. It now appears on FDA's nominated but withdrawn list; we could not confirm when the nomination was withdrawn ^[3]. It was not among the 12 peptides FDA removed from Category 2 in April 2026, and it is not on the July 2026 or February 2027 committee agendas ^{[8] [4] [5]}. Without a USP or NF monograph, an approved US drug or a bulks listing, a 503A pharmacy may not compound it ^{[9] [1]}.

We found no report that the interim peptide access policy sent to the White House in October 2026 covers thymosin alpha-1; its text is not public ^[10].

FDA's safety concerns

FDA writes that thymosin alpha-1 "may pose significant risk for immunogenicity for certain routes of administration" and that "the safety-related information is inadequate for the agency to sufficiently understand" its risks ^[3]. Immunogenicity means the immune system may react to the peptide itself, which matters for a product sold to change immune function.

Thymosin alpha-1 vs thymosin beta-4

The names are similar, but these are different peptides with different legal paths. Thymosin beta-4 fragments are sold as TB-500, which won a nonbinding 8-6-1 committee vote in July 2026 but still cannot be compounded ^{[11] [1]}. WADA names thymosin beta-4 and its derivatives under S2 ^[6]; it does not name thymosin alpha-1 ^[6]. See our TB-500 page.

Thymosin alpha-1 and WADA

The 2026 WADA list names thymosin beta-4 but not thymosin alpha-1 ^[6]. Unnamed does not mean allowed. S0 covers substances with no current government approval for therapeutic use in humans ^[6], and whether any approval outside the US counts is something your anti-doping agency decides.

Legal routes

FDA has rejected "research use only" labels as a legal shield ^[12]. See our peptide FDA status tracker, CJC-1295 and ipamorelin, which were voted down in the same 2024 meetings, BPC-157, the legal peptide price tracker, wellness injections and FDA warning letters.

Status history

• Apr 22, 2026: FDA's safety page lists it as nominated but withdrawn. The withdrawal date is not confirmed ^[3].
• Dec 4, 2024: On Dec 4, 2024, the committee voted 4 yes and 17 no on both the free base and acetate forms ^[2].
• Sep 29, 2023: FDA placed it in Category 2, citing significant safety risks ^[7].

Other peptides with no FDA review under way: Selank and CJC-1295 and ipamorelin. Peptides that did get a favorable vote in 2026: MOTS-c and Semax.

How we check

The 17 to 4 vote and the list of uses are quoted from FDA's Dec 4, 2024 minutes ^[2]. FDA's safety wording is from its safety-risk page ^[3]. Both, plus the 503A categories document, were reopened on Oct 24, 2026 to look for any new action ^[1]. None was found. See our editorial standards.