Peptide Encyclopedia / Thymosin Alpha-1
EncyclopediaThymosin alpha-1, also called thymalfasin, is a thymic peptide used as an immune modulator. Under the brand Zadaxin it is approved in roughly 30 countries for conditions such as chronic hepatitis B and as a vaccine adjuvant, but it is not FDA-approved in the US, where it exists only as a compounded or research substance. Below you'll find reported dosing, reconstitution, safety, and legal status. Educational only, not medical advice.
| Also known as | Thymosin alpha-1, Thymalfasin, Talpha1, Ta1, Zadaxin |
| Half-life | 2 hours after subcutaneous administ |
| Regulatory status | Thymosin alpha-1 (INN: thymalfasin) is NOT FDA-approved in the US. |
Thymosin alpha-1 (INN: thymalfasin) is NOT FDA-approved in the US. As the brand Zadaxin it is approved/marketed in many other countries (reported in roughly 30+ countries), for example for chronic hepatitis B and as an immune adjuvant/vaccine enhancer (e.g., in China). In the US it is available only as an unapproved/compounded or research substance.
Thymosin alpha-1 is a 28-amino-acid immunoregulatory peptide derived from prothymosin alpha and originally isolated from thymic tissue. It is reported to activate Toll-like receptor signaling (notably TLR9 and TLR2) in dendritic and other immune cells, augmenting T-helper 1 (Th1) responses, natural killer (NK) cell activity, dendritic-cell maturation, and antibody responses, while modulating regulatory T cells. The net effect is immunomodulation/immune restoration rather than broad immunosuppression. Pharmacokinetics (half-life Reported elimination half-life approximately 2 hours after subcutaneous administration (thymalfasin).): Administered subcutaneously (commonly 1.6 mg in chronic hepatitis B regimens). Thymalfasin is well absorbed subcutaneously with a relatively short plasma half-life of roughly 2 hours; immunologic effects outlast plasma presence. PK has been characterized in the context of approved (non-US) use.
Thymosin alpha-1 has been studied in many clinical trials internationally. Approved-country efficacy is best established for chronic hepatitis B and immune/vaccine adjunct use. In sepsis, evidence is mixed: the smaller ETASS RCT (n=361) suggested a 28-day mortality benefit trend, but the larger multicenter, double-blind phase 3 TESTS trial (n=1106) found NO significant difference in 28-day all-cause mortality versus placebo. Honest level: human-trials (mixed results by indication; not FDA-approved in US). Reported use: In countries where approved, a commonly REPORTED regimen for chronic hepatitis B is thymalfasin 1.6 mg subcutaneously twice weekly. Clinic/community-reported off-label immune-support use elsewhere mirrors this subcutaneous dosing. These reflect approved-country labeling and reported practice, not a US-sanctioned recommendation.
Thymosin alpha-1 is generally well tolerated in trials, with adverse events typically comparable to placebo; local injection-site reactions are the most common. Large RCTs (including TESTS, n=1106) did not show safety signals distinct from placebo. As a US-unapproved/compounded product, sourcing, sterility, and product-quality risks apply..
Known hypersensitivity to thymosin alpha-1 or formulation components, Caution in immunosuppressed transplant recipients where enhanced immune activity could be undesirable (theoretical).
No major drug interactions established; theoretical interaction with immunosuppressant therapy given its immune-stimulating action
PepWise is an informational and educational tracking tool, not medical advice and not a medical device. Thymosin Alpha-1 may be experimental, restricted, or prescription-only; many research peptides are not FDA-approved. Consult a licensed healthcare provider before starting, changing, or stopping any protocol. Operated by STC Consulting, Inc.
