Immune Support
Thymosin Alpha-1
Zadaxin · Thymalfasin · Tα1
One of the most human-tested peptides in this entire library, genuinely different territory from most of what's here. It's a real approved drug in over 35 countries, just not the UK or US, prescribed mainly for chronic hepatitis B and as a support alongside cancer treatment. The evidence is strongest for that specific use; a large 2025 trial testing it for sepsis found no clear benefit, a useful reminder that strong evidence for one condition doesn't automatically carry over to every other use it gets marketed for.
Immunomodulatory thymic with substantial but heterogeneous human trial evidence. Some older hepatitis and critical-care studies are positive, while a large modern phase 3 sepsis trial was negative.
How well studied
Tier Guide: A = Well studied, B = Some good studies, C = Early evidence & D = Barely studied
Tested in people, but in smaller or fewer studies. A decent picture, just less certain.
UK status
How you could legitimately come across it here, if at all
No authorised UK medicine contains this, and we have no record of a routine UK clinic route. Material sold online is unregulated.
Evidence strength and UK regulatory status answer different questions.
Heightened caution: this compound carries unresolved regulatory, safety or supply-chain concerns in the UK. Nothing here is a recommendation to use it.
Overview
How it works
Trains your immune system's "threat recognition" cells to work better and helps immature immune cells mature into the type that fights infection. It adjusts the immune response rather than just switching it up to maximum.
Activates toll-like 2 and 9 on dendritic and myeloid antigen-presenting cells, driving T-cell differentiation, increasing T-cell diversity, and shifting immune responses toward a Th1-polarised profile.
Reported benefits
- Randomised human trials exist in chronic hepatitis and critical-care populations
- Evidence varies by condition and trial quality; a large 2025 phase 3 sepsis trial found no mortality benefit
- General wellness or non-specific immune-boosting benefit is not established
Who it's typically used for
Timeline to results
Safety & UK access
Dosage
1.6 mg subcutaneously twice weekly is the protocol used in the chronic hepatitis B trials and in Zadaxin prescribing in the countries where it is licensed. It is a supervised clinical protocol for specific infectious and immune indications, not an MHRA-approved dose and not a wellness schedule.
Side effects
- Raised liver enzymes in people who already have liver diseasereported in the hepatitis trials; usually reflects the immune response acting on the infected liver rather than direct toxicity, but it needs monitoring
- Immune overactivation if you have an autoimmune conditionreported; a mechanism-based caution rather than a measured rate
- Injection site reactionsreported in the clinical trials of the licensed indications in other countries
Getting it in the UK
No authorised UK medicine contains this, and we have no record of a routine UK clinic route. Material sold online is unregulated.
Where it turns up
- Not routinely available in the UK
Thymalfasin has been marketed or authorised in some non-UK jurisdictions, but no authorised UK medicinal product was identified in this audit. Foreign availability does not establish UK authorisation.
Approved as Zadaxin in 35+ countries (including China and Italy) for hepatitis B, but not MHRA-licensed in the UK. Prescribable off-label by a private doctor via the unlicensed-medicines route, same pattern as Tesamorelin
MHRA: the UK regulator that assesses whether a medicine is safe and works before it can be authorised for use here. Something not being MHRA-licensed does not automatically mean it is illegal, and it does not mean it is safe.
This is background information about UK regulation, not advice about what you can or should obtain.
Evidence & sources
Why this rating?
The A to D rating shown above comes from our earlier editorial review and is still waiting to be migrated into the structured review record below. That is a gap in our record-keeping, not a sign the rating is wrong.
Evidence fingerprint
No route and indication scope has been published for this profile yet, so no fingerprint is shown.
Sources
Structured source audit not yet published for this profile. The references behind this page are being catalogued one compound at a time, and this one has not been through that process yet.
Content freshness
- Last reviewed
- 24 Sept 2026
- Regulatory status last checked
- 21 Aug 2026