Thymosin Alpha-1
Also known as Ta1, Thymalfasin, Zadaxin
A thymic immune-modulating peptide approved in many countries, with extensive international clinical data.
Medically reviewed by Dr. Jonathan Snipes, MD
Reviewed for clinical accuracy · Last reviewed July 22, 2026 · Review policy
Quick answer
Thymosin alpha-1 is a naturally occurring thymic peptide that modulates the immune system. It is approved and widely used in many countries (as Zadaxin) for hepatitis and as an immune adjunct, with a large clinical literature, but it is not FDA-approved in the US, where it is used through compounding.
- Type
- Thymic immune-modulating peptide
- US FDA status
- Not approved; approved in many other countries
- Human evidence
- Extensive international clinical data
- Evidence grade
- B (Clinical Evidence)
- Banned in sport
- Not specifically listed
Key takeaways
- →Thymosin alpha-1 is a natural thymic peptide that helps regulate immune responses, especially T-cell function.
- →It is approved in many countries and has a large clinical literature in hepatitis and as an immune adjunct in cancer and infection.
- →It is not FDA-approved in the US, so US access is through compounding.
- →It has one of the stronger human-evidence bases of the research-associated peptides, hence a B grade.
Thymosin alpha-1 stands out among peptides for the depth of its human clinical evidence. It is a naturally occurring peptide from the thymus gland that modulates immune function, and it is approved in dozens of countries for indications like chronic hepatitis and as an immune adjunct. The nuance for US readers is that it is not FDA-approved here, so despite the strong international record, US access runs through compounding.
How Thymosin Alpha-1 works
Thymosin alpha-1 enhances immune function primarily by supporting the maturation and activity of T-cells and dendritic cells, helping the immune system respond to infection and, in some settings, cancer. Unlike many research peptides, these effects are supported by controlled human trials in specific conditions.
What the evidence shows, by use
Each use is graded on the same A-E scale, based on human-trial quality rather than popularity.
Chronic hepatitis / antiviral immune support
BClinical EvidenceSupported by international clinical trials and approvals; this is its best-evidenced use.
General immune enhancement / longevity
CEmerging Human DataPopular off-label use with weaker, less specific evidence than its approved indications.
Dosing
In the countries where it is approved, thymosin alpha-1 is given by subcutaneous injection at defined doses for defined indications. US compounded protocols vary. Given its immune effects, dosing should be individualized by a licensed clinician, particularly in anyone with autoimmune disease or on immune-modulating therapy.
Side effects
- •Injection-site reactions · Common
- •Fatigue · Reported
- •Transient flu-like symptoms · Reported
- •Immune-related effects · Reported
Legal & regulatory status
Thymosin alpha-1 is not FDA-approved in the US (though approved in many other countries) and is accessed here through compounding, by prescription.
Is Thymosin Alpha-1legal? Full regulatory status →Where to get it: TeleRanked independently ranks the telehealth providers that offer clinician-prescribed peptides. See our Peptide Therapy rankings. We rank providers, we do not sell compounds, and rankings are never for sale.
Frequently asked questions
Is thymosin alpha-1 FDA-approved?+
Not in the United States. It is approved in many other countries and, in the US, is used through compounding.
Is thymosin alpha-1 the same as TB-500?+
No. Thymosin alpha-1 is an immune-modulating peptide with strong clinical evidence. TB-500 is derived from thymosin beta-4, a different peptide involved in tissue repair.
How we grade evidence
Grade B: Clinical Evidence. Human randomized or controlled trials support use, but it is not FDA-approved for this purpose. Our A-E scale reflects the strength of human evidence, not how popular a compound is.
Sources
- 1.Compounding and the FDA: Questions and Answers · U.S. Food & Drug Administration
- 2.Drugs@FDA: FDA-Approved Drugs database · U.S. Food & Drug Administration