Thymosin α-1 (Thymalfasin): Evidence, Side Effects, and Regulatory Status (2026)
Thymosin α-1 (Thymalfasin) is FDA-approved (some markets). Evidence grade: moderate. This page is clinically reviewed.
TL;DR / Quick Facts
Thymosin α-1 (Thymalfasin) is Thymosin α-1 is a 28-amino-acid thymic peptide. FDA-approved in some markets (Zadaxin) for chronic hepatitis B and as an immune adjuvant. In the U.S., it is available via 503A compounding. FDA status: FDA-approved (some markets). Typical use cases: immune, autoimmune, longevity. Evidence grade: moderate. Dosing is per the FDA label — set by your clinician. Common side effects: see below. Medriva editorial stance: follow the FDA label; do not use off-label without clinical supervision.
What it is
Thymosin α-1 (Thymalfasin) is a member of the Immunomodulatory thymic peptide class. Thymosin α-1 modulates T-cell maturation and function, increasing T-helper 1 (Th1) cytokines and supporting immune surveillance.
What the evidence says
Evidence for Thymosin α-1 (Thymalfasin) is moderate. Multiple phase 3 trials and post-market data support the labeled indications.
[Detailed evidence breakdown in the corresponding claim or pillar pages is linked at the bottom of this page.]
What it's used for
Commonly discussed uses of Thymosin α-1 (Thymalfasin):
- Immune — moderate evidence.
- Additional uses listed in the linked use-case hubs; evidence varies by indication.
For the full list, see the linked use-case hubs below.
Typical dosing
Thymosin Alpha 1 dosing is determined by the approved label, indication, comorbidities, current medications, and clinician judgment. Medriva does not publish individualized dosing instructions or titration schedules. Review the current prescribing information and make changes only with a licensed clinician.
Side effects and risks
- Common: Side effects vary by compound and indication; review the approved label or profile-specific safety data with a clinician.
- Serious: Seek urgent care for severe allergic symptoms, chest pain, severe abdominal pain, persistent vomiting, or other severe reactions.
- Long-term unknowns: For non-approved or research-use compounds, long-term human safety data may be limited.
Regulatory status
- FDA-approved use(s): Approved in some markets for chronic hepatitis B and as an immune adjuvant. In the U.S., 503A compounding is the legal route.
- Compounded availability: see 503A vs 503B explainer
- Research-use-only (RUO) availability: n/a
- Banned in sport: see WADA & sports explainer
Cost and access
Thymosin α-1 (Thymalfasin) is available by prescription; see the cost page for the relevant indication. For pricing, see our cost pages or the GLP-1 price/supply tracker where applicable.
Who it might be appropriate for
Adults with a relevant diagnosed condition or clinical goal, under the supervision of a licensed clinician, who have no contraindications. Thymosin α-1 (Thymalfasin) is not for self-experimentation.
Who should not use it
Contraindications vary by compound, indication, pregnancy status, comorbidities, and current medications. For the full list, see the contraindications checklist and discuss with your clinician.
Medriva editorial stance
We describe the literature. We do not promote Thymosin α-1 (Thymalfasin) as a cure, treatment, or performance enhancer. We do not recommend it for self-experimentation. We do recommend that readers (a) understand the evidence grade (moderate), (b) understand the regulatory status (FDA-approved (some markets)), and (c) discuss with a licensed clinician before acting.
How to talk to a clinician
See our guide on how to talk to a clinician for a templated conversation.
Frequently Asked Questions
Is Thymosin α-1 (Thymalfasin) FDA-approved?
FDA-approved (some markets). See the regulatory status section above for details.
Does Thymosin α-1 (Thymalfasin) work for immune?
Evidence is moderate. See the linked use-case hub for the full breakdown.
What are the side effects?
See the side effects section above. Discuss with your clinician.
How much does Thymosin α-1 (Thymalfasin) cost?
See the cost pages or the GLP-1 price/supply tracker where applicable.
Can I buy Thymosin α-1 (Thymalfasin) online?
By prescription only. Medriva does not sell peptides.
Author + Clinical reviewer
Author: Sara Iqbal, MS Clinical reviewer: Jonathan Reeves, MD Last reviewed: 2026-06-05
Next steps
- Review the evidence grade and regulatory status before making decisions about Thymosin Alpha 1.
- Bring this page to a licensed clinician if you are discussing benefits, risks, or alternatives.
- Subscribe to the Medriva Peptide Brief for evidence and regulatory updates.
Related use-case hubs
Related comparisons
Editorial process
This page follows the Medriva Editorial Policy and the Clinical Review Methodology. Page last reviewed: 2026-06-05. Author: Sara Iqbal, MS. Clinical reviewer: Jonathan Reeves, MD.
Current source updates
For new regulator actions, compounding-policy changes, warning letters, shortage updates, and sports-rule changes, review the Peptide Tracker before relying on older summaries.
