Thymosin Alpha-1

Areas of active research — not promised effects

Each tag links to other compounds with research into that goal. Research use only: these are areas of study, not human-use claims.

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Thymosin alpha-1 has never received FDA approval as a drug product in the United States. It was placed on the FDA Category 2 bulk drug substances list (substances that may present significant safety risks for compounding under 503A), restricting compounded preparation. Based on regulatory actions in early 2026, certain peptides including thymosin alpha-1 were removed from Category 2 around April 2026, but this removal does not constitute approval for compounding or human use. A PCAC review is scheduled (July 23–24, 2026 meeting at FDA White Oak Campus, docket FDA-2025-N-6895) where inclusion on the 503A Bulks permitted list will be assessed. A December 2024 PCAC meeting considered thymosin alpha-1 (free base and acetate), with FDA proposing they not be included on the 503A Bulks List. The final regulatory outcome remains pending. Until a rulemaking is concluded, thymosin alpha-1 cannot be legally compounded for human use in the US under 503A.

Transparent blend · bci-1.0 · never paid-placement

Primary name

Thymosin Alpha-1

Origin

Thymosin alpha-1 (Tα1) is the N-terminal 28-amino-acid fragment of prothymosin alpha, originally isolated from bovine thymic tissue by Allan Goldstein and colleagues in the 1970s. The synthetic form (thymalfasin; brand name Zadaxin, SciClone Pharmaceuticals) is manufactured via solid-phase peptide synthesis and is chemically identical to the endogenous fragment. It carries CAS 62304-98-7, molecular formula C129H215N33O55, and a molar mass of approximately 3108 Da. The peptide is N-terminally acetylated and contains 28 residues. It has been approved as a pharmaceutical product (Zadaxin) in more than 35 countries including China, Italy, the Philippines, and various markets in Asia, South America, and the Middle East for the treatment of chronic hepatitis B and as an immune restoration agent. It has not received FDA approval in the United States.

Registry IDs

PubChem CID

16130571

CAS

62304-98-7

InChIKey

NZVYCXVTEHPMHE-ZSUJOUNUSA-N

ChEMBL

CHEMBL2103979

Molecular formula

C129H215N33O55

Molar mass

3108.3 g/mol

Monoisotopic

3106.5041281 Da

InChIKey

NZVYCXVTEHPMHE-ZSUJOUNUSA-N

Appearance

White to off-white lyophilized powder

Solubility

Freely soluble in water at physiological pH; highly hydrophilic due to multiple …

Sequence not available in current seed.

Stability: Stable as lyophilized powder under cold-chain conditions. Reconstituted solution is relatively stable at neutral pH but susceptible to aggregation under prolong

Vial sizes

1.6 mg · 5 mg

Purity grades

≥99% (HPLC)

Salt forms

Free base (primary)

• GHS hazard class on file
• PPE & spill response
• Disposal guidance
• Not-for-human-consumption posture

How much research exists, and of what maturity — never a verdict on whether it works.

Mechanism of action

• Thymosin alpha-1 acts as a biological response modifier by engaging Toll-like receptors (TLR2, TLR3, TLR4, TLR7, and TLR9) on myeloid and plasmacytoid dendritic cells, triggering activation of the downstream IRF3 and NF-κB signaling cascades
• This TLR-mediated signaling promotes dendritic cell maturation, augments type I interferon production, and enhances antigen presentation, thereby bridging innate and adaptive immune responses
• In the adaptive compartment, Tα1 facilitates differentiation of immature thymocytes into functionally competent CD4+ helper and CD8+ cytotoxic T-cell subsets, in part by upregulating surface expression of CD2, CD3, CD4, and CD8 on progenitor cells
• The net immunological effect is context-dependent immunomodulation: in states of immune deficiency or anergy (as seen in chronic hepatitis, sepsis-associated immune suppression, and advanced cancer), Tα1 shifts the immune balance toward activation, while preclinical data also suggest it can dampen excessive inflammatory responses by promoting regulatory T-cell activity under hyperinflammatory conditions

Pharmacokinetics (ADME)

Half-life

Approximately 2 hours after subcutaneous administration (human volunteer pharmacokinetics study; PubMed PMID 10027483 — retrieved via web search, not in compound topPmids; reviewer to confirm)

Clearance

Proteolytic degradation by tissue and circulating aminopeptidases to constituent amino acids; volume of distribution approximately 5–8 L, consistent with extracellular fluid distribution

PK–PD note: Tmax approximately 1–2 hours post-subcutaneous injection across formulations. No significant drug accumulation occurs at twice-weekly dosing schedules, consistent with the short half-life. A PASylated…

Reading the evidence

• Evidence quality and gaps vary by application — see the cited grades above.
• Indexed-article counts span all evidence tiers, not only completed human trials.
• No first-party human-dosing, efficacy, or benefit claims are made here.

Key reviews & evidence-gap sources

• Dominari A, et al. Thymosin alpha 1: A comprehensive review of the literature. World J Virol. 2020;9(5):67–78. — Anchoring narrative review covering mechanism, clinical trials, and regulatory status
• Li J, et al. Thymosin alpha 1: Biological activities, applications and genetic engineering production. Peptides. 2010;31(11):2151–2158. — Mechanism-focused review detailing TLR/MyD88, p38 MAPK, NF-κB, IRF7, Akt, IDO pathways
• Wu J, et al. The efficacy and safety of thymosin α1 for sepsis (TESTS): phase 3 trial. BMJ. 2025;388:e082583. — Largest completed Phase 3 RCT (n=1106); found no clear evidence of 28-day mortality reduction in sepsis
• Systematic review/meta-analysis: Thymosin alpha-1 in moderate to critical COVID-19. 2023. — Pooled 8 studies; reported lower mortality RR 0.59 but high heterogeneity (I²=84%)
• Wu J, et al. Thymosin alpha1 based immunomodulatory therapy for sepsis: systematic review and meta-analysis. Crit Care. 2013. — Earlier sepsis meta-analysis preceding the TESTS trial

5 registered trials — 0 currently recruiting.

Phase 4
NCT02883595
Efficacy of Thymosin Alpha 1 on Improving Monocyte Function for Sepsis

COMPLETED

Phase 3
NCT04320238
Experimental Trial of rhIFNα Nasal Drops to Prevent 2019-nCOV in Medical Staff

UNKNOWN

Phase 2
NCT06056804
Neoadjuvant Chemoradiotherapy Combined With PD-1 Inhibitor and Thymalfasin for pMMR/MSS Locally Advanced Mid-low Rectal Cancer

ACTIVE_NOT_RECRUITING

Phase 2
NCT02787447
Radiotherapy Combined With Thymosin for Metastatic NSCLC Patients Who Showed Stable Disease After First Line TKI Therapy

UNKNOWN

Phase 2
NCT02366208
Phase II Trial for Combination Treatment of PEG-Tα1 and Adefovir for HBeAg Positive Chronic Hepatitis B

COMPLETED

Summary (literature)

Across decades of international clinical use in approved markets and multiple Phase 2–4 trials encompassing thousands of patients, thymalfasin (Zadaxin) has demonstrated a favorable safety profile. The most common adverse event is mild injection-site reaction (erythema, transient…

WADA status

Not specifically listed by name on the WADA 2026 Prohibited List. Thymosin alpha-1 is an immunomodulatory peptide and does not fall within the explicitly named …

Dominant research route: Subcutaneous (SC)

Human pharmacokinetics in healthy Caucasian volunteers (n=9, 900 µg/m², single- and 5-day multiple-dose, 3-way crossover) and multiple randomized controlled trials in chronic hepatitis B and C (Zadaxin label, pooled RCTs)

Bioavailability: Well absorbed after SC injection; mean tmax 1–2 h; Cmax 30–80 µg/L; AUC(0–inf) 95–267 µg·h/L; elimination half-life <3 h; apparent volume of distribution Vz/f ~30–40 L (extracellular distribution). No accumulation observed between single- and multiple-dose.

Dominant research and labeled route. Zadaxin (thymalfasin) is formulated as a lyophilized 1.6 mg vial reconstituted to 1.6 mg/mL for SC injection; pivotal hepatitis B/C trials used 1.6 mg SC twice weekly. PK comparable to prior Japanese-volunteer and cancer-patient data but influenced by formulation.

Mentioned in secondary/aggregator literature as having been studied without pharmacokinetic or clinical advantage over SC; no primary human PK or RCT retrieved for IV

Bioavailability: No IV pharmacokinetic parameters retrieved from primary sources; SC is the characterized route.

IV route is referenced in aggregator/secondary sources as studied but offering no advantage over SC; lacking primary citation. Treated as community-tier, unverified.

Animal & human figures are kept visibly separate so studied animal doses are never misread as human guidance.

Sorted A–Z by vendor — never by price

Weekly median $/mg from the live vendor crawl.

Researched storefront prices, bucketed

p25 $8.20 · median $13.00 · p75 $13.60 · 8 researched vendors

Legit, COA-backed band: $7.00–$16.20/mg.

Value rule: don't just buy the cheapest — a price under $3/mg is a red flag. Pair price with COA and independent-test grade.

Estimated cost of research (10 mg)

Vial (best researched price)

$40

Bacteriostatic water (generic estimate)

$6

Syringes / supplies (generic estimate)

$12

What each test proves — general guidance, plus this compound's researched purity data

Purity on the current market (researched)

99.349%–99.86% HPLC purity reported across independent Janoshik Analytical tests of research-grade Thymosin Alpha-1 samples (Panda Peptides batch and a Peptide Sciences 3mg vial). A separate aggregator-reported HPLC test of a Pura Peptide 10mg vial reported 99.85% purity.

Independent labs cited for this compound

No FDA recalls or market withdrawals specific to Thymosin Alpha-1 were found in the FDA Recalls, Market Withdrawals, and Safety Alerts database during research. This is an honest 'none found' result, not an assertion of absence.

Buyer red-flag checklist

• Marketed as COVID-19 treatment/prevention without FDA approval (FDA/FTC warning letter, Dec 2020).
• Classified by FDA as an unapproved new drug; no FDA-approved application in effect for Thymosin Alpha-1 in the U.S.
• Research-grade (RUO) products sold online with human-use/dosing claims and reconstitution instructions.
• Independent lab testing observed underfill/underdosing in at least one commercial vial (2.66mg vs 3mg advertised).

GMP vs research-grade: the chemistry (SPPS + HPLC + MS) is identical — the difference is the quality system.

Underdosing / mislabeling: A single de-identified independent lab test (Janoshik, referenced via a community review aggregator) reported a Thymosin Alpha-1 vial advertised as 3mg containing only 2.66mg of peptide (purity 99.86%), indicating underfill/underdosing in that one sample. Sample size is too small (n=1 observed underdosed among limited public tests) to compute a reliable prevalence; value set to null.

• FDA Import Alert 66-41 authorizes Detention Without Physical Examination (DWPE) of unapproved new drugs promoted in the U.S. The alert applies generally to unapproved new drug products, including peptides marketed without FDA approval; Thymosin Alpha-1 is not individually named on the Red List in the retrieved alert text, but the alert's scope encompasses unapproved peptide drug products promoted for human use.66-41
• An RUO label is not an import exemption — CBP judges actual intended use.
• Lyophilized powder is ambient-stable in transit; temperature control needed for > 7-day transit.
• US-warehouse vendors dodge import scrutiny — they cost more but ship more reliably.

Every item dated & sourced

Not prohibited. WADA Prohibited List prohibits Thymosin-β4 and its derivatives (e.g., TB-500) under S2.3 (growth factors and growth factor modulators), but Thymosin Alpha-1 is not listed as a prohibited substance. The Court of Arbitration for Sport (Essendon case) distinguished Thymosin Alpha (immune booster, not prohibited) from Thymosin Beta-4 (prohibited).

No granted patents identified in current seed. Composition-of-matter coverage is limited given the peptide's synthetic origin.

• IACUC / IRB research context
• RUO buyer responsibilities & documentation
• Veterinary / alternative-use where lawful
• Jurisdiction-aware "who may lawfully obtain"

What people discuss

Reported concerns — discussion, not established effects

Reading caveats

• Self-selection bias: dramatic responders over-represented in long-COVID communities
• Subjective outcome reporting: users rarely verify with biomarkers (CD4/CD8, NK cell activity)
• Vendor-affiliated aggregator content present (realpeptides.co)
• No placebo-controlled validation in community reports
• Conflation of degradation/contamination effects with peptide effects

Manually researched from reddit, youtube— theme weights are research estimates, not live counts; aggregated & de-identified. No individual posts, quotes, or usernames are ever shown.

Relative research / market volume — populated once the activity stream is wired

Inline tooltips for lyophilized, RUO, EU/mg, SPPS, 503A and more.

Toggle plain-language ↔ scientific in the header.

• How to read a COA
• Free base vs acetate
• Understanding evidence grades

Synthetic 28-amino-acid thymic peptide approved in 35+ countries for hepatitis B and immune deficiency; studied in sepsis, oncology, and viral infections. Approximately 577 articles are indexed (literature last scanned 2026-05-29). US regulatory status: Not FDA-approved; previously Category 2 bulk drug substance; removed from Cat-2 list ~April 2026; PCAC review pending. Research use only.

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