Thymosin Alpha-1

One of the best-evidenced peptides in this guide. It rebalances the immune system rather than simply revving it up.

Evidence: AApproved what's this?
Grade A. Approved in 35+ countries; 80+ trials and over 11,000 patients.
Also known as: Tα1 · Thymalfasin · Zadaxin
Class: Synthetic 28-amino-acid thymic peptide; immunomodulator. Approved in 35+ countries.

The 30-second version

WhatA single, precisely defined thymic peptide isolated in the 1970s, made synthetically.

Proven forChronic hepatitis B, immune deficiency, and as an adjunct to cancer therapy (outside the US).

The honest catchThe list of claims is very broad, and the largest sepsis trial missed its main endpoint.

What it is

Tα1 is unrelated to TB-500 (Thymosin β4), apart from the name, and it isn’t the same as Thymalin, which is a multi-peptide extract. Sold as Zadaxin, it’s approved across Asia, parts of Europe and South America. In a genuine regulatory paradox, it has never been FDA-approved despite orphan designation in 1991.

How it works

TLR2 and TLR9 on dendritic cells, the immune system’s command cells, are activated.

Defence up. A Th1 response, plus T-cell and NK-cell maturation, against viruses, infection and tumours.

Balance. Through the enzyme IDO, it promotes regulatory T-cells that calm overreaction.

Both at once. Strengthens weak immunity and tempers excessive immunity.

Outcome. More competent, balanced immune function, which is what fails with age and immunosuppression.

What the research shows

Hepatitis B: meaningfully higher sustained viral response than placebo, which established it across Asia². Cancer: more than 40 trials as an adjunct to chemotherapy or immunotherapy, with preserved immune counts, better quality of life and, in some, longer survival. Vaccines: antibody responses in the elderly improved by about 40%. Sepsis: the TESTS trial (1,106 patients, BMJ 2025) is the largest Tα1 RCT. It did not significantly reduce 28-day mortality overall, which tempers earlier hopes from smaller studies³. The safety record across more than 11,000 patients is consistently clean^1,2.

Its safety and core immune effect are firmly established. The size of the benefit in each separate disease is less certain.

Evidence at a glance

Use	Grade	Best evidence	Main gap	Read
Chronic hepatitis B	AApproved	Higher sustained viral response²	Regional data	Approved
Cancer adjunct	BHuman trials	Preserved immunity; some survival gains	Variable design	Supportive
Sepsis	BHuman trials	TESTS: no overall mortality reduction³	Subgroups debated	Not proven
Immune ageing	CClinical off-label	Restores competence; vaccine response	Extrapolated to healthy	Reasonable

Dosing: what has been reported

Not a recommendation. These figures describe what was studied or what circulates in practice, kept separate so you can see how solid each one is. Speak with a qualified clinician before acting on any of it.

Setting	Figure	Route	Grade
Approved (hepatitis)	1.6 mg twice weekly for 6–12 months	Subcutaneous	A
Cancer / sepsis research	1.6–3.2 mg twice weekly, or per protocol	Subcutaneous	B
Community loading	1–1.5 mg daily for 10–30 days	Subcutaneous	D
Community maintenance	1.6 mg twice weekly	Subcutaneous	D

The 1.6 mg dose is unusually consistent across settings, a sign of an established pharmaceutical standard.

Preparing & storing

Reconstitute with bacteriostatic water (or as the label directs), keep cold and away from light, and don’t shake.

Reported side effects

Mild injection-site redness or discomfort, often the only effect
Occasional minor, passing reactions
No significant treatment-related adverse events at therapeutic doses in large trials

It’s used alongside interferon in hepatitis and as a vaccine adjuvant. Immunosuppressants oppose its effect. Track a CBC with lymphocytes, and T-cell subsets if available.

Who should avoid it

Organ transplant on immunosuppression: specialist guidance only
Active autoimmune disease: specialist input
Pregnancy and breastfeeding: medical guidance only

Regulatory status checked Oct 2026

Body	Status	Detail
FDA (US)	Not approved	Investigational; restricted compounding since 2023.
EMA (EU)	Not centrally	National approvals, e.g. Italy.
Other markets	Approved	Zadaxin in 35+ countries (China, SE Asia, S. America).
WADA	Not prohibited	Permitted, unlike TB-500.

The NexGen read

An immune peptide with real clinical weight

Tα1 is a defined, approved, very safe molecule with a large trial record. It’s best supported for restoring immune competence in people who have lost it. Some disease-specific claims, including sepsis, are less certain than its marketing suggests.

References

Goldstein AL, Low TL, McAdoo M, et al. Thymosin α1: isolation and sequence analysis of an immunologically active thymic polypeptide. PNAS. 1977;74(2):725–729.
Garaci E, Pica F, Rasi G, Favalli C. Thymosin α1: from bench to bedside. Ann N Y Acad Sci. 2007;1112:225–234.
Wu J, et al. Thymosin α1 in patients with sepsis (TESTS): a multicentre randomized controlled trial. BMJ. 2025.