What is thymosin alpha 1?

Thymosin alpha 1 is a naturally occurring, highly acidic 28-residue peptide from the thymus, and thymalfasin is its synthetic N-acetylated form. Goldstein's group isolated it from thymosin fraction 5, a calf thymus extract, and described it in 1977 as "heat stable, highly acidic" and one of several peptides that may take part in T cell regulation and differentiation. ^[1] MeSH classifies thymalfasin as an immunologic adjuvant. ^[2]

Two facts explain most of the literature. First, researchers in 1979 reported it was 10 to 1,000 times as active as the crude fraction 5 in their T cell assays, which is why the field moved from a thymus extract to one defined peptide. ^[9] Second, the peptide was later made by chemical synthesis, so clinical programmes ran on a synthetic molecule with the natural sequence. A 2010 review traces that programme from small physician-sponsored studies of the impure extract in immune deficiency to phase 3 trials of synthetic thymosin alpha 1 in the United States, Italy and China. ^[10]

Thymosin alpha 1 in 10mg vials is in stock with a batch certificate.

Studies describe thymosin alpha 1 acting on dendritic cells through Toll-like receptor (TLR) signalling and on T cells through interleukin-2 receptor expression. Reviewers call it pleiotropic because the reported effects span several cell types. ^[11]

The main lines of mechanistic work:

1. T cells, in vitro (1990). In human blood lymphocytes stimulated with a mitogen, synthetic thymosin alpha 1 increased the number of high-affinity IL-2 receptors without changing their affinity. It had no effect without the mitogen. ^[12]
2. Dendritic cells and fungal infection, mice (2004). Thymosin alpha 1 induced maturation and IL-12 production in dendritic cells through the MyD88-dependent pathway, involving distinct TLRs, and protected transplanted mice from aspergillosis. ^[13]
3. Viral sensing, mice (2007). In murine cytomegalovirus infection, the effect ran through TLR9 and MyD88 in plasmacytoid dendritic cells and activated interferon regulatory factor 7. ^[14]
4. Tolerance (2007 review). The same Perugia group reported that thymosin alpha 1 induced indoleamine 2,3-dioxygenase activity in dendritic cells, and they describe it as an endogenous regulator of inflammation and tolerance. ^[4]

A structural line of work adds a membrane step. NMR studies found the peptide unstructured in water, inserting its N-terminus into membrane regions exposed by phosphatidylserine, and binding serum albumin through its C-terminal region. ^[11] Most of this mechanism comes from one research network and from mouse models. It describes proposed biology, and no single pathway has been confirmed as the explanation for any clinical result.

Thymosin alpha 1 is a linear 28-residue peptide with an acetylated N-terminal serine and a free C-terminal acid. It contains no cysteine, so it has no disulfide bonds. ^[2]

We checked each identifier against PubChem on 29 September 2026. ^[2] The parent-protein position comes from the human prothymosin alpha record: after the starting methionine, its first 28 residues are the thymosin alpha 1 sequence. ^[15] Rat work in 1984 first showed that the thymus holds a larger protein of about 112 residues with this sequence at its N-terminus, and concluded thymosin alpha 1 was a fragment generated while fraction 5 was being prepared. ^[3]

The structure is flexible. In a water and trifluoroethanol mixture, NMR showed an alpha-helix from residues 14 to 26 and a distorted helical region across the first 12. ^[16] In plain water it has no stable structure. ^[11] The 1984 study also found synthetic thymosin alpha 1 ran on gel filtration at an apparent molecular weight of 10,000 to 11,000, and the authors proposed it forms oligomers in solution. ^[3]

Thymosin alpha 1 has been examined across cell, mouse and human studies, including several randomised controlled trials, which is more human data than most research peptides have. The trials cover chronic hepatitis B and C, sepsis, melanoma and vaccine response, and their results are mixed. A 2009 review reported that thymalfasin was approved in over 35 countries for hepatitis B and C and as an immune stimulant and adjuvant. ^[17]

The vaccine line is the thinnest to read from abstracts. The 1989 abstract is truncated before its results, and a 2007 review by the same investigators summarises animal and human trials as showing enhanced vaccine responses. ^[23] Cancer work is broad and uneven: a 2026 scoping review found 26 clinical publications since 2016, mostly retrospective studies and case reports from China. ^[24]

Every row describes what one study reported for its own population, using clinical-grade material under trial conditions. None of it is a claim about a research vial.

The thymosin alpha 1 evidence does not establish a clinical effect with confidence in any condition we reviewed. The trials are real and numerous, and the best-designed ones are the least positive. Four limits matter most.

1. The largest trial found no mortality difference. TESTS enrolled 1,106 adults with sepsis and reported a hazard ratio of 0.99 for 28-day mortality. Its authors found "no clear evidence" of a reduction. ^[5] The 2025 meta-analysis pooled a mortality benefit, but its high-quality and multicentre subgroups did not show one, and it judged the total sample size inadequate. ^[22]
2. Hepatitis B certainty is low. The 2026 Cochrane review included trials published from 1991 to 2018, four of them industry-funded, and concluded the authors were "not sure" whether thymosin alpha 1 changes mortality or adverse events. ^[6]
3. Results depend on setting. A 2001 review described hepatitis B and C trials as mixed, with one hepatitis C trial finding no difference from placebo in ALT normalisation. ^[25] Reviewers in 2015 noted that the amount given, the schedule, combinations and endpoints had not been properly settled. ^[26]
4. No published trial used research-grade material. Every human study used a pharmaceutical product. A 1999 study even found exposure differed between three pharmaceutical formulations of the same peptide. ^[19] What is in a research vial is a separate question, and the batch certificate is what answers it.

Published trials of thymosin alpha 1 report few adverse-event differences from control groups, and several abstracts list no specific event types. These are the reported observations, each tied to its study.

• Sepsis, phase 3 (TESTS, 2025). In 1,106 adults, no secondary or safety outcome differed statistically significantly between thymosin alpha 1 and placebo. ^[5] The abstract does not list event types.
• Hepatitis B (Japan, 2005). In 316 adults, all adverse drug reactions were rated mild, and most involved fluctuating liver enzymes. Incidence was similar in the two study groups. ^[20]
• Hepatitis B (Cochrane, 2026). Pooled serious adverse events gave a risk ratio of 0.72 across 5 trials and 1,056 participants, rated low certainty. ^[6]
• Melanoma (2010). Adding thymosin alpha 1 to chemotherapy and interferon alfa did not lead to additional toxicity in 488 patients. ^[21]
• Influenza vaccine in older men (1989). No toxicity was observed in either group. ^[18]
• Earlier trials (2001 review). Most studies observed only local irritation where the peptide entered the skin. ^[25]
• Cancer studies (2026 scoping review). Safety reporting was inconsistent, and one case described severe multisystem immune-related toxicity during combination treatment, without establishing that thymosin alpha 1 caused it. ^[24]

These are clinical-trial observations in specific populations, reported as the published record.

Thymosin alpha 1 is not named in the Poisons Standard. We searched the June 2026 instrument (F2026L00633), which commenced on 1 June 2026, for thymosin alpha 1 and thymalfasin and found no individual entry. The only thymosin entry is thymosin beta 4, which is listed in Schedule 4 and Appendix D clause 5. ^[7] A missing entry is a dated search result about the Poisons Standard only. It says nothing about medicine registration.

For sport, thymosin alpha 1 is not named on the WADA 2026 Prohibited List, effective 1 January 2026. ^[8] The List's S0 class prohibits at all times any pharmacological substance not addressed elsewhere that has no current approval by any governmental regulatory health authority for human therapeutic use. ^[8] Whether S0 applies turns on current approval status. A 2009 review reported approvals in over 35 countries, ^[17] and we did not verify current approvals, so athletes should check with Sport Integrity Australia. Our guide to Australian peptide law and the Poisons Standard explains each schedule.

No. Thymosin alpha 1 and TB-500 come from different proteins and differ in size, sequence and legal status. The shared word "thymosin" dates from the 1970s, when several peptides were named after the thymus extract they came from. ^[1]

The thymosin alpha 1 column comes from PubChem ^[2] and the TB-500 figures from its own PubChem record. ^[27] Scheduling is from the June 2026 instrument ^[7] and the WADA index. ^[8] The full TB-500 picture is in our explainer on what TB-500 is and how it relates to thymosin beta-4. Both compounds sit in our recovery research peptides range.

No published stability study covers lyophilised research-grade thymosin alpha 1, so storage follows general peptide practice: sealed, cold, dry and dark. Bachem advises keeping peptides long term as lyophilisate in a tightly closed container below -15°C, and letting the container reach room temperature in a desiccator before opening, because peptides absorb moisture. ^[28]

The sequence helps. Thymosin alpha 1 has no cysteine, methionine or tryptophan, the residues Sigma-Aldrich flags as prone to air oxidation. ^[29] It does end in one asparagine, and Sigma-Aldrich lists asparagine among residues that make peptides unstable in solution. ^[29] A reconstituted solution is therefore the weak point: keep it refrigerated, protect it from light, avoid repeated freezing and thawing, and label it with the date, solvent and concentration in mg per mL. Our peptide storage guide covers each step.

On solvents, Bachem classifies a peptide as acidic when its acidic groups outnumber its basic ones. Such peptides "may often be solubilized in PBS at pH 7.0 to 7.4" at 1 mg/mL or less, or started in a small amount of a basic solvent. ^[30] By that count thymosin alpha 1 is strongly acidic: 10 acidic groups against 4 basic, because its N-terminus is capped. Structural studies dissolved it in water and in water with trifluoroethanol. ^[16][11] We stock BAC Water, sterile water with 0.9% benzyl alcohol, in 3ml vials for A$8, and no study in our set tested thymosin alpha 1 in it. The peptide reconstitution guide covers solvent choice and concentration arithmetic.

Peptides Collective sells thymosin alpha 1 for laboratory research use only, in 10mg vials from A$118. Stock ships from Western Australia with tracking.

Every batch is tested by an independent lab before it goes on sale. The certificate reports purity by HPLC and identity by mass spectrometry, and it is published under the batch number printed on the vial. You can search the certificate of analysis library by that batch number and match the report to the vial in your hand.

Read the certificate against the structure table above. The identity result should match an acetylated 28-residue peptide of about 3108 g/mol, and our guide on how to read a peptide certificate of analysis explains the HPLC trace, the mass spectrum and net peptide content. The thymosin alpha 1 product page links the certificate for the current batch.

Thymosin alpha 1 is a 28-residue, acetylated, highly acidic peptide cut from prothymosin alpha, with a short half-life of about 2 to 3 hours in human studies. It has decades of human trials behind it, and the largest and best-graded of them report no clear effect or low-certainty evidence. In Australia it is not named in the June 2026 Poisons Standard, and WADA's 2026 List does not name it. For a research vial, the batch certificate is the evidence that settles what is inside.