Peptides · Thymic immunomodulatory peptide

Thymosin alpha-1: what the studies show

Every line below comes from a study, label or regulator record, checked by two models, with the source linked. Information, not medical advice. For adults 18+.

What it is

Thymosin alpha-1 (Ta1, also called thymalfasin) is a 28-amino-acid peptide first found in the thymus gland. The version used in trials is made synthetically and given under the skin. It is an immune modulator, not a growth or repair peptide.^[1]^[2]
It is a different molecule from thymosin beta-4 and the TB-500 fragment, despite the similar name. Evidence for those does not apply to Ta1, and the reverse is also true.^[2]

Bottom line

Thymosin alpha-1 has been tested in many human trials, mostly in China and mostly in hospital patients with sepsis, pancreatitis, hepatitis or cancer. The largest, best-designed trials were negative on their main goals. It is not FDA approved, and FDA's advisory committee voted 4 yes to 17 no on letting pharmacies compound it.^[1]^[3]^[4]^[5]

What the human studies found

Sepsis, TESTS (double-blind RCT, 1,106 adults with sepsis at 22 Chinese centres, 28 days): 28-day death was 23.4% on Ta1 versus 24.1% on placebo (hazard ratio 0.99, p=0.93). Subgroups pointed both ways: worse in people under 60 and better in people with diabetes. The authors found no clear evidence that Ta1 reduces mortality.^[1]
Sepsis, pooled: a 2025 meta-analysis of 11 RCTs (967 on Ta1, 960 controls) found lower 28-day death (odds ratio 0.73), but the high-quality and multicentre subgroups showed no benefit.^[6]
Severe acute pancreatitis (double-blind RCT, 508 people, Ta1 1.6 mg every 12 hours for 7 days): infected pancreatic necrosis occurred in 15.7% on Ta1 versus 18.1% on placebo (p=0.48), so no benefit on the main outcome.^[3]
Hepatitis C that had failed earlier treatment (double-blind RCT, 552 people, Ta1 1.6 mg twice weekly plus peginterferon and ribavirin for 48 weeks): sustained virus clearance was 12.7% versus 10.5% on placebo (p=0.41). In those who completed all 48 weeks it was 41.0% versus 26.3% (p=0.048), a subgroup finding.^[4]
Hepatitis B with compensated cirrhosis (RCT, 690 people, Ta1 plus entecavir for 52 weeks versus entecavir alone): decompensation, liver cancer or death were similar in both groups over a median 38 months. A 2026 Cochrane review of Ta1 for chronic hepatitis B rated the evidence low or very low certainty for the outcomes it reported.^[7]^[8]
COVID-19 (open-label RCT, 49 hospitalised patients with low oxygen and low lymphocytes): recovery was not significantly faster, though CD4 T-cell counts rose faster on Ta1.^[9]

Known risks and side effects

In the large trials, serious side effects did not differ significantly from placebo (sepsis and pancreatitis trials).^[1]^[3]
In TESTS, mortality was higher on Ta1 than placebo in people under 60 (hazard ratio 1.67) in a prespecified subgroup analysis. This may be chance but was not explained.^[1]
FDA says compounded Ta1 may carry a significant risk of immune reactions for some routes, that peptide impurities add risk, and that safety information is inadequate for FDA to understand the extent of safety issues.^[10]

Legal status

As of 2026-10-09 Ta1 is not an FDA-approved drug. FDA's category 2 page lists it among bulk substances that may pose significant risks if compounded.^[10]
On 2024-12-04 the Pharmacy Compounding Advisory Committee considered Ta1 free base and acetate for the 503A bulks list. FDA evaluated 12 uses including hepatitis B and C, HIV, COVID-19, sepsis and cancers. The committee voted 4 yes and 17 no on each form. The vote is advisory.^[5]^[2]
A 2020-12-07 FDA warning letter to Paradigm RE LLC said its Thymosin Alpha 1 sold with COVID-19 claims was an unapproved and misbranded new drug.^[11]