Thymosin alpha-1: evidence, half-life, and how to track it

Thymosin alpha-1 is a 28-amino-acid peptide first isolated from calf thymus and sequenced in 1977 (Goldstein et al., Proceedings of the National Academy of Sciences, 1977); thymalfasin is its synthetic form (Chien and Liaw, Expert Review of Anti-infective Therapy, 2004). A 2001 review reports a serum half-life of about 2 hours (Ancell et al., American Journal of Health-System Pharmacy, 2001). A 2009 review describes it as approved in over 35 countries for hepatitis B and C (Goldstein and Goldstein, Expert Opinion on Biological Therapy, 2009), but DailyMed lists no US label for it.

By Tessaro Pty Ltd, the maker of Pepti · Last reviewed October 2026

This page is a reference, not a protocol. It sets out what the published research reports and in which settings, what a half-life of about two hours means for a record, and what a clean log holds. It gives no dose figures and no schedule, and the section below explains why that is deliberate rather than an omission.

Reference

Property	Value
Class / type	Acidic 28-amino-acid peptide first isolated from thymosin fraction 5, a calf thymus extract; thymalfasin is the synthetic form — (Goldstein et al., 1977; Chien and Liaw, 2004)
Evidence base	Randomised trials in chronic hepatitis B (Chien and Liaw, 2004), pooled in a 2026 Cochrane review that rated the evidence low to very low certainty (Naing et al., 2026); a phase 3 sepsis trial of 1,106 adults (Wu et al., 2025); a COVID-19 meta-analysis of 8 studies (Soeroto et al., 2023)
Half-life	About 2 hours in serum, with peak levels within two hours and a return to baseline within 24 hours, as reported in a 2001 review — (Ancell et al., 2001)
Regulatory status	Described in 2009 as approved in over 35 countries for hepatitis B and C and as an immune stimulant (Goldstein and Goldstein, 2009); no label listed on DailyMed (checked October 2026)

What the research shows

Thymosin alpha-1 was isolated from calf thymus and sequenced in 1977: a heat-stable, highly acidic molecule of 28 amino acid residues, one of several peptides in thymosin fraction 5 that may take part in the regulation, differentiation and function of T cells (Goldstein et al., Proceedings of the National Academy of Sciences, 1977). Thymalfasin is the same 28-amino-acid peptide made synthetically (Chien and Liaw, Expert Review of Anti-infective Therapy, 2004).

Its proposed mechanism comes from the laboratory. In vitro studies report effects on T-cell production and maturation, on Th1 cytokines such as interferon-gamma and interleukin-2, and on natural killer cell activity (Chien and Liaw, Expert Review of Anti-infective Therapy, 2004); later studies reported increased MHC class I and Toll-like receptor expression (Garaci, Annals of the New York Academy of Sciences, 2007). These describe immune signalling in experimental systems, not a clinical benefit in themselves.

The older trials cited here are in chronic viral hepatitis. A 2004 review of seven randomised controlled studies of thymalfasin alone in chronic hepatitis B reported a significantly higher sustained response after six months of treatment than in untreated controls, with a trend for complete virological response to build gradually after treatment ended (Chien and Liaw, Expert Review of Anti-infective Therapy, 2004). Hepatitis C was less consistent: a 2001 review found no significant difference in liver-enzyme (ALT) normalisation against placebo in one trial, and higher response rates when it was combined with interferon than with interferon alone in two others; it summarised the hepatitis B and C trials as mixed, with effects on illness and death still to be shown (Ancell et al., American Journal of Health-System Pharmacy, 2001).

The most recent pooled analysis is a 2026 Cochrane review of 10 randomised trials in 1,349 adults with chronic hepatitis B, published between 1991 and 2018. It found that thymosin alpha-1 may reduce all-cause mortality and serious adverse events, but it rated the evidence very low certainty for every outcome except serious adverse events (low), and its authors concluded that they are not sure whether it reduces mortality or serious adverse events (Naing et al., Cochrane Database of Systematic Reviews, 2026).

The phase 3 sepsis trial is negative. In TESTS, a double-blind, placebo-controlled phase 3 trial of 1,106 adults with sepsis at 22 centres in China, 28-day all-cause mortality among the 1,089 analysed was 23.4% with thymosin alpha-1 and 24.1% with placebo (hazard ratio 0.99), and no secondary or safety outcome differed significantly; the authors found no clear evidence that it reduces 28-day mortality in sepsis. A prespecified subgroup analysis suggested a possible difference by age, with higher mortality on thymosin alpha-1 in under-60s (hazard ratio 1.67), and by diabetes, with lower mortality in people with diabetes (hazard ratio 0.58); subgroup signals like these need confirming (Wu et al., BMJ, 2025).

The COVID-19 evidence is less settled. A 2023 meta-analysis pooling eight studies of moderate to critical COVID-19 found lower mortality with thymosin alpha-1, but with high heterogeneity between studies and no difference in the need for mechanical ventilation or in hospital stay; its authors called for randomised trials to verify the finding (Soeroto et al., Inflammopharmacology, 2023).

The regulatory picture differs by country. A 2009 review describes thymosin alpha-1 as approved in over 35 countries for hepatitis B and C and as an immune stimulant and adjuvant, and as still in late-stage clinical testing in the United States and Europe at the time (Goldstein and Goldstein, Expert Opinion on Biological Therapy, 2009). DailyMed, the US National Library of Medicine’s label database, lists no label for it (checked October 2026), so there is no US label to point to.

On compounding, the US FDA’s list of bulk substances that may present significant safety risks, current as of April 2026, places thymosin alpha-1 among substances previously in its “category 2” whose nominations were withdrawn (FDA, 2026). That is not an approval.

Sources (10)

Goldstein AL, et al., Proceedings of the National Academy of Sciences of the United States of America, 1977 — isolation and sequence analysis of thymosin alpha-1 from calf thymus. Find on PubMed
Chien RN, Liaw YF, Expert Review of Anti-infective Therapy, 2004 — thymalfasin for the treatment of chronic hepatitis B. Find on PubMed
Ancell CD, et al., American Journal of Health-System Pharmacy, 2001 — thymosin alpha-1: pharmacology, pharmacokinetics and clinical trials (review). Find on PubMed
Garaci E, Annals of the New York Academy of Sciences, 2007 — thymosin alpha-1: a historical overview. Find on PubMed
Wu J, et al., BMJ, 2025 — TESTS: multicentre, double-blind, randomised, placebo-controlled phase 3 trial in sepsis. Find on PubMed
Soeroto AY, et al., Inflammopharmacology, 2023 — thymosin alpha-1 in moderate to critical COVID-19 (systematic review and meta-analysis). Find on PubMed
Goldstein AL (Allan), Goldstein AL (Adam), Expert Opinion on Biological Therapy, 2009 — emerging clinical applications of thymosin alpha-1 (review). Find on PubMed
Manning MC, et al., Pharmaceutical Research, 2010 — stability of protein pharmaceuticals (review). Find on PubMed
Naing C, et al., Cochrane Database of Systematic Reviews, 2026 — thymosin alpha-1 for people with chronic hepatitis B (systematic review of 10 randomised trials). Find on PubMed
U.S. Food and Drug Administration, Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks, content current as of 22 April 2026 — lists thymosin alpha-1 among nominations withdrawn from category 2. Read on FDA.gov

What a half-life of about two hours means for your record

A 2001 review reports that thymosin alpha-1 is rapidly absorbed, reaching peak serum concentrations within two hours, with a serum half-life of approximately 2 hours and blood levels back to baseline within 24 hours (Ancell et al., American Journal of Health-System Pharmacy, 2001). The review summarises the figure rather than reporting a new pharmacokinetic study, and its abstract does not say which route or product the figures come from, so they describe the peptide in serum, not the product or form you may have.

For a record, the point is the shape rather than the number. A peptide reported back to baseline in serum within a day leaves no lasting blood level to read, while the effects studied in the trials above were read over weeks and months. The dated log of what you entered and when is therefore the only timeline that lines up with those slower changes; a clearance curve on its own says little about them.

That is also how this site handles the number. The half-life calculator on this site projects clearance from a value you enter yourself. Neither the site nor the app supplies the figure or presents one as settled.

Storage and handling

This is general handling, not product-specific instruction. Peptides degrade by both chemical and physical routes, and formulations are stabilised differently in aqueous solution than in the dried (lyophilized) state (Manning et al., Pharmaceutical Research, 2010). Material supplied as a dried powder is generally the more robust form and is inert until a diluent is added; once in solution it is more vulnerable, so it is kept cold and dark, used within a limited window, protected from repeated freeze-thaw, and handled with clean technique.

The record-keeping point is the one Pepti cares about: the moment a powder becomes a solution, two facts are created that you will need later and will not otherwise remember — the diluent volume you added and the date you mixed it. Writing them down at the time is the difference between a vial record you can trust and one you are guessing about.

How to track it in Pepti

Pepti is built for exactly this situation: a compound you already have a figure for, supplied in a vial that needs a careful record. If you mix it yourself, the free reconstitution calculator on this site (not the app) takes the variables you enter — the amount in the vial and the diluent volume — and returns the concentration and the draw volume for the figure you already hold. Every input is a value you supply; none is a dose the site suggests.

From there the injection-site rotation tracker keeps a 12-site sequence so each injection lands somewhere other than the last, and the vial record keeps its lot and dates. The app holds the record and the history; the clinical figures stay with you.

Why this page has no dosing section

There is no US label for thymosin alpha-1 on DailyMed, so there is no US-labelled dose to point to. The regimens in the trials above were set for specific populations — people with chronic viral hepatitis, adults in intensive care with sepsis — under investigator supervision, and approvals elsewhere apply to their own indications and their own clinicians. Lifted out of those settings and printed on a reference page, they stop being findings and become instructions nobody actually gave.

Pepti is a record-keeping tool. It logs the figure you already have with the date, time, site and vial, and remembers where the last injection went — but it does not supply or calculate the figure, for this compound or any other. The figure belongs to you and whoever directs your use; the record is what we are for.

What a clean thymosin alpha-1 record holds

A peptide that clears from serum within hours, studied for effects read over weeks, is only legible over time, so the record earns its keep through completeness and consistency rather than precise timing of any one entry.

Date and time — the actual clock time, not “morning”. Patterns are invisible until written down.
The figure you already have — whatever was decided with whoever directs your use, in the unit you think in. This page does not supply it.
Route and form — injected or otherwise, and whether the vial was a powder you reconstituted or arrived as a solution. The forms are not interchangeable in a record.
The date any figure changed — not the figure itself, the date. The dates of change are what turn a list of entries into a readable history.
Injection site — which of the twelve zones, so the next one goes somewhere else.
Vial records — if the vial arrived as a powder, the diluent volume, resulting concentration and the date it was mixed, so a later draw is not a guess.
Measured trend — whatever is actually being measured, recorded the same way each time. A single reading means little; the line across weeks is the part worth keeping.

The free reconstitution calculator on this site (not the app) converts the figures you already have into a draw volume and a count of doses per vial; the peptide tracking app guide shows how to keep your log, the site sequence and your notes on one timeline.

Common questions

What is thymosin alpha-1?

Thymosin alpha-1 is a heat-stable, highly acidic peptide of 28 amino acids, first isolated from calf thymus and sequenced in 1977 (Goldstein et al., Proceedings of the National Academy of Sciences 1977). It is one of several peptides in thymosin fraction 5, a thymus extract, that may take part in T-cell regulation and function.

Is thymalfasin the same as thymosin alpha-1?

Yes. Thymalfasin is the synthetic form of the same 28-amino-acid peptide, originally isolated from thymosin fraction 5, a bovine thymus extract (Chien and Liaw, Expert Review of Anti-infective Therapy 2004). It is not the same as TB-500, a different peptide.

What is thymosin alpha-1's half-life?

A 2001 review reports a serum half-life of approximately 2 hours, with peak serum concentrations within two hours and blood levels back to baseline within 24 hours (Ancell et al., American Journal of Health-System Pharmacy 2001). The half-life calculator on this site works from a value you enter yourself, never one we supply.

Does thymosin alpha-1 work for sepsis?

A large phase 3 trial found no clear benefit. In TESTS, 1,106 adults with sepsis were randomised to thymosin alpha-1 or placebo, and 28-day all-cause mortality among the 1,089 analysed was 23.4% versus 24.1% (hazard ratio 0.99), with no secondary or safety outcome differing significantly (Wu et al., BMJ 2025).

Is thymosin alpha-1 approved?

A 2009 review describes it as approved in over 35 countries for hepatitis B and C and as an immune stimulant (Goldstein and Goldstein, Expert Opinion on Biological Therapy 2009). DailyMed, the US National Library of Medicine's label database, lists no label for it (checked October 2026).

Does Pepti tell me what dose to take?

No. Pepti supplies no dose figures for thymosin alpha-1 or for anything else. It records the figure you already have from whoever directs your use, with the date, time, injection site and vial, and keeps the 12-zone site sequence. The record is ours; the figure is not.

This page is a reference on published evidence and record-keeping. It does not recommend thymosin alpha-1 or any other substance, and it provides no dose figure, no titration amount, and no schedule. DailyMed lists no US label for thymosin alpha-1.

The Pepti peptide tracker for iPhone keeps the log, the site sequence, the vial records and your notes in one place.

Not medical advice. Pepti is a record-keeping tool, not a medical device.

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