# Thymosin Alpha-1: A Weighed Appraisal of the Thymalfasin Research > Thymosin Alpha-1 is a 28-amino-acid thymic immune peptide with decades of human data — strongest in chronic hepatitis B, while the largest rigorous sepsis trial was null. The record, appraised. A sober reading of four decades of trials: where the evidence is strongest, where it is suggestive, and where the largest rigorous study came back null. Every quantitative claim is cited. ## The short version Thymosin Alpha-1 (also written Tα1; the synthetic drug form is called thymalfasin) is a small immune-signaling peptide — a chain of 28 amino acids — that the body makes from a larger parent protein. It is not a muscle, growth, or performance compound. It works on the immune system: it helps certain immune cells (dendritic cells, which act like the body's alarm-callers) mature and switch on T cells, while also engaging a calming, regulatory pathway. People have studied it for chronic hepatitis B, sepsis, COVID-19, cancer support, and autoimmune conditions. The honest summary: the evidence is real but uneven, strongest in chronic viral hepatitis, and the single largest, most careful sepsis trial found no survival benefit [3]. It is not approved for sale in the United States, though it is approved in roughly 35 other countries [4]. What people report — including the downsides — is on [the effects page](/effects). ## What the Thymosin Alpha-1 record shows Thymosin Alpha-1 is a 28-amino-acid, N-terminally acetylated thymic peptide first isolated from calf thymus and sequenced by Goldstein and colleagues in 1977 [1]. It is cleaved inside the body from a larger 113-amino-acid precursor called prothymosin alpha, and the small acetyl tag on its front end (the "acetyl" mark) is essential for it to work [1]. Across four decades it has been tested in dozens of human trials, with the most consistent results in chronic viral hepatitis. In hepatitis B, combining Thymosin Alpha-1 with the antiviral lamivudine produced markedly higher rates of hepatitis B e-antigen seroconversion than lamivudine alone — 45.1% versus 15.2% across eight trials and 583 patients (P<0.00001) [14]. A separate meta-analysis reached the same direction: higher virological response and fewer viral breakthroughs with the combination [13]. This is the part of the record where the signal is strongest and most reproducible. The peptide's appeal is its mechanism. It acts at the meeting point of innate and adaptive immunity — restoring effector immunity when the immune system is exhausted, while damping over-inflammation through a regulatory arm [5]. That dual character is the lens this site reads it through, and it is laid out in detail on the [thymosin alpha 1 mechanism of action](/mechanism-of-action) page. ## Where the strongest trial came back null The discipline of an appraisal is holding the positive results apart from the negative ones. The largest, most rigorous test of Thymosin Alpha-1 to date is the phase-3 TESTS trial: 1,106 adults with sepsis across 22 centers, double-blind and placebo-controlled, published in the BMJ in 2025. It found no statistically significant difference in 28-day all-cause mortality — 23.4% on the peptide versus 24.1% on placebo, a hazard ratio of 0.99 (95% CI 0.77–1.27, P=0.93) [3]. That result matters because earlier sepsis work looked promising. The 361-patient ETASS trial in 2013 reported 28-day mortality of 26.0% with the peptide versus 35.0% in controls — about a 9-point absolute difference, but one that only reached marginal significance [2]. TESTS, larger and more rigorous, did not confirm it. The lesson the data teaches is to keep "studied" and "proven" clearly separated, and not to assume a survival benefit outside the settings where the evidence is firmest. ## A different molecule from its frequently-confused relatives Thymosin Alpha-1 is constantly confused with other "thymosin" peptides, and the distinction is real. It is a different molecule from thymosin beta-4 (sold as research material under the label TB-500), which is a 43-amino-acid actin-binding peptide with a different sequence, size, and function — and it is thymosin beta-4, not Thymosin Alpha-1, that appears on anti-doping watchlists. In one classic experiment the two peptides did opposite things: Thymosin Alpha-1 enhanced lymphocyte proliferation through helper T cells, while thymosin beta-4 suppressed it through suppressor T cells [9]. Thymosin Alpha-1 is also distinct from thymulin (a zinc-dependent nonapeptide), thymopentin (a pentapeptide), thymalin (a separate bovine thymic-extract preparation), and prothymosin alpha (its own larger precursor). The full disambiguation, side by side, is on [Thymosin Alpha-1 research](/research). The downsides people actually report appear on the [Thymosin Alpha-1 effects](/effects) page; the full source list is on [Thymosin Alpha-1 references](/references). --- Thymosin Alpha-1 Reviews is an evidence-appraisal desk that weighs the published thymalfasin record — strongest in chronic hepatitis B, null in the largest sepsis trial — held by no clinic and selling no product.