Immune & inflammation
Thymosin alpha-1
A thymic immune peptide approved in dozens of countries for specific indications, but never approved in the US — and marketed far beyond any approval.
Also known as: thymalfasin, Zadaxin, Tα1
Evidence passport
Last reviewed 2026-08-23
- Evidence level
- L3Early human
- Confidence
- Moderate confidence
- Human efficacy
- 45/100
- Human safety
- 45/100
- Regulatory status
- Approved — specific region(s)
- Development
- Approved
- Routes
- SC injection
- Evidence base
- Includes human data
- Furthest stage
- Approved
- Source curation
- Sources fully curated
- Clinical maturity
- Approved in multiple non-US regions for specific indications; studied in oncology and infectious disease settings
Overview
Clinical maturity: Approved in multiple non-US regions for specific indications; studied in oncology and infectious disease settings
Routes & formulations
Studied / approved routes
Approved products abroad (e.g. thymalfasin) are subcutaneous injections for their specific licensed indications. Anything else sold online is outside approved supply.
Route availability is not evidence of efficacy, and evidence from one route does not transfer to another. The Registry never provides dosing or sourcing information.
Peptide lifecycle
Discovery
Preclinical
Phase I
Phase II
Phase III
Approved
Approved in parts of Asia-Pacific, Latin America, Eastern Europe and the Middle East for various indications; never approved by the FDA.
What it is
A 28-amino-acid peptide originally isolated from thymic tissue, developed as an immune-response modifier.
What people claim
- Boosts immune function
- Adjunct benefit in hepatitis and some cancers
- General immune 'optimisation' in healthy people
What the evidence actually says
This is a real medicine in many countries with genuine clinical trial history — which makes it the most over-extrapolated compound in its class. Region-specific approvals for defined diseases do not translate into evidence for healthy-person immune enhancement, and the FDA has never approved it.
Human evidence
- Clinical trials in hepatitis B/C and as an adjunct in some oncology settings, largely supporting its regional approvals.
- No evidence base supporting general 'immune boosting' in healthy people.
Preclinical evidence
- Immune cell assays and animal models of infection and tumour immunology.
Animal and cell findings are Level 1–2 evidence.
Mechanism and pathways
- Modulates T-cell maturation and dendritic-cell function; effects on TLR signalling described.
Safety and unknowns
- Generally described as well tolerated within its approved indications abroad.
- Products sold outside approved supply carry unverified quality.
Cancer relevance
Monitored in trials; not demonstrated in humans
Regulatory status
Not FDA-approved. The FDA's 2024 advisory review notes approvals in parts of Asia-Pacific, Latin America, Eastern Europe and the Middle East for various indications. Those approvals are region- and indication-specific; they do not generalise to 'immune boosting' in healthy people or to US availability.
Evidence grade
Small, short or uncontrolled human studies. Suggestive, not conclusive.
What would change our rating?
- A regulatory decision in a major Western region.
- Large independently run trials in the marketed use cases.
References and sources
- Regulatory / labelFDA — Thymosin alpha-1 briefing material (PCAC 2024)
Source hierarchy: regulatory documents and trial registries first, peer-reviewed work next, sponsor material flagged as non-independent. We never use supplier or clinic marketing as evidence, and where a verified source has not yet been curated we say so rather than inventing one.
Evidence change history
No recorded changes yet. Baseline position set on 2026-08-23.