Thymosin alpha-1 is one of the few peptides in this market with large, well-run trials, and both large trials were negative. In TESTS, sepsis mortality did not move. In TRACE, infected pancreatic necrosis did not move. In the US it has no compounding pathway.
Key points
- In TESTS (sepsis, 1,106 patients), 28-day mortality was 23.4% vs 24.1% with placebo; HR 0.99 [1].
- In patients under 60 the HR was 1.67 (95% CI 1.04 to 2.67): a subgroup, but in the wrong direction [1].
- In TRACE (necrotizing pancreatitis, 508 patients), infected necrosis did not change: 15.7% vs 18.1% [2].
- Cochrane 2026 (hepatitis B): very low certainty; “we are not sure” it reduces mortality [4].
US status (October 2026): Thymosin alpha-1 is not FDA-approved and has no compounding pathway; FDA’s advisory committee voted 4 to 17 against listing it in December 2024. MDside providers do not prescribe it. See the thymosin alpha-1 status page.
Thymosin alpha-1 has a real pharmaceutical history
Unlike most trendy peptides, thymosin alpha-1 has been studied for decades in hepatitis B [4] and is approved in more than 35 countries for hepatitis B and C, according to a 2009 review [7]. That history gives it credibility. It is also why the large trials of recent years carry so much weight: they are the test that history invites, and few peptides in this market have faced one.
TESTS found no mortality benefit in sepsis
TESTS was a phase 3, double-blind, placebo-controlled trial at 22 centers in China, with 1,106 patients with sepsis (1,089 in the modified intention-to-treat analysis). 28-day mortality was 23.4% with thymosin alpha-1 vs 24.1% with placebo (HR 0.99; 95% CI 0.77 to 1.27; P = 0.93) [1].
The subgroups showed something uncomfortable. In patients under 60, the HR was 1.67 (1.04 to 2.67), a possible harm signal. In patients with diabetes, the HR was 0.58 (0.35 to 0.99) [1]. Subgroups generate hypotheses. They do not settle anything. The trial was partly funded by SciClone Pharmaceuticals [1], the company that also supplied the thymosin alpha-1 in TRACE [2].
- HR 0.99: 28-day mortality in sepsis (TESTS, 1,106 patients) [1]
- HR 1.67: under-60 subgroup [1]
- 15.7 vs 18.1%: infected necrosis in pancreatitis (TRACE) [2]
TRACE found no benefit in pancreatitis
In TRACE, 508 patients with predicted severe necrotizing pancreatitis received thymosin alpha-1 or placebo. Infected pancreatic necrosis was 15.7% vs 18.1% (P = 0.48): a negative result [2]. A later analysis by lymphocyte count suggested possible benefit in the subgroup with lymphocytes ≥0.8 × 10⁹/L, but its authors note the subgroup was not prespecified and must be confirmed in a prospective trial [3].
Hepatitis B and COVID-19 data are low certainty
The 2026 Cochrane review pooled 10 trials with 1,349 patients with chronic hepatitis B (1991 to 2018). Mortality (3 trials, 907 patients) showed an RR of 0.53 (0.29 to 0.96), but with very low certainty: “we are not sure whether thymosin-α1 … reduces all-cause mortality” [4]. In COVID-19, a meta-analysis of 8 studies gave RR 0.59 with very high heterogeneity (I² = 84%); the authors call for randomized trials [5].
The paradox. Thymosin alpha-1 is one of the few peptides in this market with large, well-run trials. Those very trials were negative [1][2]. In the US, the FDA lists it among substances whose nomination was withdrawn, with safety information it considers “inadequate” [6].
The other side. Thymosin alpha-1 has decades of clinical use outside the US [7]. In hepatitis B, the Cochrane review found lower mortality (RR 0.53), albeit with very low certainty [4], and in TESTS the diabetes subgroup showed an HR of 0.58 [1]. For its supporters, these signals justify studies targeted at specific populations rather than dismissing it.
What this means for you
Keep thymosin alpha-1 off your menu, including immune support bundles sold during cold and flu season. Foreign approvals and hepatitis data do not create a US pathway, and a “research use only” label does not either: see why that label is no shield. If a patient asks, the honest summary is two large negative trials and one subgroup signal in the wrong direction. For what an immune or wellness offering can lawfully include, see peptide programs.
References
- Wu J, et al. The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ. 2025;388:e082583. PMID 39814420. Link
- Ke L, et al. Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial. Intensive Care Med. 2022;48(7):899-909. PMID 35713670. Link
- Ke L, et al. 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. EClinicalMedicine. 2023;58:101915. PMID 37007743. Link
- Naing C, et al. Thymosin-α1 for people with chronic hepatitis B. Cochrane Database Syst Rev. 2026;9(9):CD014610. PMID 42713852. Link
- Soeroto AY, et al. The efficacy of thymosin alpha-1 therapy in moderate to critical COVID-19 patients: a systematic review, meta-analysis, and meta-regression. Inflammopharmacology. 2023;31(6):3317-3325. PMID 37845598. Link
- U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Link
- Goldstein AL, Goldstein AL. From lab to bedside: emerging clinical applications of thymosin alpha 1. Expert Opin Biol Ther. 2009;9(5):593-608. PMID 19392576. Link
This is general information, not medical or legal advice. Rules vary by state and change. Confirm your own facts with counsel.