Is Thymosin Alpha-1 approved anywhere as a drug?

Yes. Thymosin Alpha-1 is approved in several Asian and some European markets as the branded product Zadaxin (SciClone Pharmaceuticals) for specific hepatitis B and C indications and, in some jurisdictions, as a cancer immunotherapy adjuvant. It is not FDA-approved for any therapeutic indication in the United States. Compounded Tα1 sold as a research chemical in the US is a distinct product from the approved pharmaceutical. Note: following an HHS announcement in February 2026, thymosin alpha-1 was moved to a compounding-eligible category in the US, though it remains without an approved indication.

What are the known risks and side effects of Thymosin Alpha-1?

In controlled trials for hepatitis B and C, adverse event rates were generally low and comparable to placebo. The most common reported adverse events were mild, transient injection-site reactions and occasional flu-like symptoms. A theoretical risk exists for individuals with autoimmune disease, as immunomodulation via TLR pathways could provoke inappropriate immune activation. Patients on immunosuppressive regimens (e.g., organ transplant recipients) should be especially cautious. The safety profile in community users self-administering for immune support or wellness has not been evaluated in controlled trials.

What is Thymosin Alpha-1 different from TB-500?

They are distinct compounds from different thymosin subfamilies. Thymosin Alpha-1 (Tα1) is a 28-amino-acid peptide primarily associated with immune modulation, studied in hepatitis and oncology contexts. TB-500 is a synthetic analogue of Thymosin Beta-4, a 43-amino-acid protein associated with tissue repair and cell migration. They share the 'thymosin' name because both were originally characterised from thymic tissue, but their mechanisms, evidence bases, and applications are different.

How strong is the evidence for Thymosin Alpha-1?

Evidence for specific hepatitis B indications is supported by multiple randomised controlled trials and regulatory approvals in several markets, though the study populations and contexts are specific. For community-discussed wellness and immune optimisation uses in healthy adults, evidence is insufficient: there are no adequately powered, placebo-controlled trials in healthy populations. The COVID-19 retrospective analysis (Liu et al., 2020, PMID 32442287) generated interest but is not a basis for clinical conclusions.

Is Thymosin Alpha-1 legal to buy or use?

Thymosin Alpha-1 is not FDA-approved in the United States and is sold there as a research chemical. Following an HHS announcement in February 2026, it was moved to a compounding-eligible category in the US. It is an approved pharmaceutical in some Asian and European markets for specific indications under the brand name Zadaxin. Regulatory status varies by country and is subject to change; verify current status with a qualified legal or clinical professional.

Compounding · Cat 1Thymic peptide · 28 aa

Thymosin Alpha-1

28-amino-acid thymic peptide · N-terminal fragment of prothymosin alpha; approved as Zadaxin in select markets for hepatitis B/C

A 28-amino-acid thymic peptide produced endogenously as the N-terminal fragment of prothymosin alpha; first isolated in 1977 and approved as Zadaxin (SciClone) in select Asian and European markets for specific hepatitis indications. Reportedly investigated for immune modulation, hepatitis B and C management, and oncology support; compounding-eligible in the US since February 2026. Randomised controlled trial data exist for hepatitis B/C applications, though quality and scope vary; evidence for other investigated applications is less well established.

Studies tracked

This page is editorial content summarising reported literature. It does not constitute medical advice and should not be used to guide treatment decisions. Nothing on this page states that any substance cures, treats, or prevents any condition.

Safety first

Side effects & risks

Thymosin Alpha-1 (Tα1) has a more characterised human safety record than most research peptides in this class, because it has been evaluated in randomised controlled trials for hepatitis B and C, certain malignancies, and, more recently, severe sepsis. This does not mean it is without risk; it means the risk profile is better characterised than for compounds lacking any controlled human trial data.

In the most extensively studied indications — chronic active hepatitis B and hepatitis C — adverse event rates in randomised controlled trials were generally low and comparable to placebo. Hepatitis B trial data from multiple randomised trials that informed Asian-market approvals reported injection-site reactions (mild, transient) and occasional flu-like symptoms as the most common adverse events. These were assessed in populations with specific hepatitis-related immunological status.

A retrospective analysis by Liu et al. (2020, Clinical Infectious Diseases, vol. 71; PMID 32442287) evaluated Tα1 use in COVID-19 patients and reported a possible mortality benefit in severe cases. This was a non-randomised retrospective cohort from a single centre during an early-pandemic period with variable standard-of-care practices; the finding has not been replicated in prospective randomised trials and cannot be interpreted as establishing Tα1 as a COVID-19 treatment.

The immunostimulatory mechanism that is hypothesised to underlie Tα1's clinical effects also carries theoretical risk: inappropriate immune activation in individuals with autoimmune disease or organ transplant recipients (who require immunosuppression) could be clinically significant. Published trial protocols generally excluded individuals with active autoimmune disease; community users should note this exclusion.

Thymosin Alpha-1 is not FDA-approved for any therapeutic indication in the United States. It is approved in some Asian and European markets for specific hepatitis indications, under the brand name Zadaxin (SciClone Pharmaceuticals). The approved indications and the research-chemical use cases discussed in community forums are not equivalent. Individuals obtaining compounded Tα1 should note that its compounding status in the United States was reopened following an HHS announcement in February 2026, though it remains without an approved indication in the US.

Evidence summary

Hepatitis B (human, RCT data)

Mixed

Multiple RCTs and meta-analyses (Zhang et al., 2009, PMID 19467157) show modest but statistically significant seroconversion improvements in e-antigen positive HBV patients; findings specific to HBV genotypes and treatment-naive or lamivudine-treated populations.

Hepatitis C (human, limited)

Weak / none

Early pilot data exists but is limited in quality and scale; mixed results do not constitute an adequately powered efficacy demonstration.

Cancer immunotherapy adjuvant

Weak / none

Early-phase trials in NSCLC, melanoma, and HCC report immune parameter improvements in some studies but not consistent clinical endpoint benefit; no Phase III signal established.

General wellness / immune optimisation (healthy adults)

Weak / none

No adequately powered, placebo-controlled trials in healthy populations; extrapolation from hepatitis trial data is not supported by peer-reviewed evidence.

Latest studies

All 1 →

Study · Thymosin Alpha-1Weak / none

Peptide Therapies in Thyroid Health: Emerging Applications in Endocrine and Immune Modulation.

This narrative review, published in Integrative Medicine, examines whether certain peptide-based therapies might one day play a role in managing thyroid disorders — particularly autoimmune conditions like Hashimoto's thyroiditis, where patients often continue to experience symptoms even after standard thyroid hormone replacement brings their lab values back to normal. The authors reviewed existing research on four peptides: thymosin alpha-1, thymosin beta-4, BPC-157, and growth hormone secretagogues (compounds that stimulate the body's own growth hormone release). For each, they explored the biological pathways that could, in theory, connect the peptide's known actions — such as immune regulation, inflammation control, or tissue repair — to processes relevant to thyroid health. The review found that the available evidence consists mainly of animal studies, laboratory experiments, and small exploratory human reports. No large, well-designed clinical trials focused specifically on thyroid outcomes have been completed for any of these peptides. The authors note that safety profiles differ across the peptide classes and that clinical use in thyroid disease remains investigational. The review concludes that while there are plausible biological reasons to investigate these compounds further, the evidence needed to draw clinical conclusions simply does not yet exist. Well-designed human trials are needed before the role — if any — of peptide therapies in thyroid care can be...

Integrative medicine (Encinitas, Calif.)n=——April 1, 2026

Community discussion

See all 1 discussion →

1 community discussion

Community-reported · not verified

These are synthesised observations from public forum discussions. They are community-reported, not clinically verified, and should not inform any health decision. The peptide does not cure, treat, or prevent any condition based on these reports.

r/PeptidePathways · Mar 21positive

“TA1 + KPV might be one of the most underrated stacks”

A user argues that stacking thymosin alpha-1 (TA1) with KPV is an underrated combination.

Protocol Discussion

Reported protocols (with caveats)

⚠ Editor's caveat

These dose ranges describe what people are reported to do, not what is established as safe or effective. There is no FDA-approved indication. Self-injection of unscheduled peptides carries known and unknown risks. Talk to a clinician.

USE	ROUTE	COMMON DOSE	FREQUENCY	TYPICAL CYCLE
Hepatitis B (approved clinical protocol — not community use)	SC injection	1.6 mg	2× weekly	26–52 weeks (with concomitant antiviral)
Immune support (community-reported)	SC injection	0.5–1.6 mg	2–3× weekly	4–12 weeks

Frequently asked questions

Is Thymosin Alpha-1 approved anywhere as a drug?: Yes. Thymosin Alpha-1 is approved in several Asian and some European markets as the branded product Zadaxin (SciClone Pharmaceuticals) for specific hepatitis B and C indications and, in some jurisdictions, as a cancer immunotherapy adjuvant. It is not FDA-approved for any therapeutic indication in the United States. Compounded Tα1 sold as a research chemical in the US is a distinct product from the approved pharmaceutical. Note: following an HHS announcement in February 2026, thymosin alpha-1 was moved to a compounding-eligible category in the US, though it remains without an approved indication.
What are the known risks and side effects of Thymosin Alpha-1?: In controlled trials for hepatitis B and C, adverse event rates were generally low and comparable to placebo. The most common reported adverse events were mild, transient injection-site reactions and occasional flu-like symptoms. A theoretical risk exists for individuals with autoimmune disease, as immunomodulation via TLR pathways could provoke inappropriate immune activation. Patients on immunosuppressive regimens (e.g., organ transplant recipients) should be especially cautious. The safety profile in community users self-administering for immune support or wellness has not been evaluated in controlled trials.
What is Thymosin Alpha-1 different from TB-500?: They are distinct compounds from different thymosin subfamilies. Thymosin Alpha-1 (Tα1) is a 28-amino-acid peptide primarily associated with immune modulation, studied in hepatitis and oncology contexts. TB-500 is a synthetic analogue of Thymosin Beta-4, a 43-amino-acid protein associated with tissue repair and cell migration. They share the 'thymosin' name because both were originally characterised from thymic tissue, but their mechanisms, evidence bases, and applications are different.
How strong is the evidence for Thymosin Alpha-1?: Evidence for specific hepatitis B indications is supported by multiple randomised controlled trials and regulatory approvals in several markets, though the study populations and contexts are specific. For community-discussed wellness and immune optimisation uses in healthy adults, evidence is insufficient: there are no adequately powered, placebo-controlled trials in healthy populations. The COVID-19 retrospective analysis (Liu et al., 2020, PMID 32442287) generated interest but is not a basis for clinical conclusions.
Is Thymosin Alpha-1 legal to buy or use?: Thymosin Alpha-1 is not FDA-approved in the United States and is sold there as a research chemical. Following an HHS announcement in February 2026, it was moved to a compounding-eligible category in the US. It is an approved pharmaceutical in some Asian and European markets for specific indications under the brand name Zadaxin. Regulatory status varies by country and is subject to change; verify current status with a qualified legal or clinical professional.