What is the difference between thymalin and thymosin alpha-1?

Thymalin is an extract of calf thymus containing a mixture of short peptides. Thymosin alpha-1 (thymalfasin) is a single synthetic peptide of 28 amino acids with a defined sequence. Both are studied as immune modulators, but their composition, evidence and approval status differ.

Is thymalfasin the same as thymosin alpha-1?

Yes. Thymalfasin is the international non-proprietary name (INN) for synthetic thymosin alpha-1, which has the same sequence as the natural peptide.

What is the half-life of thymosin alpha-1 and thymalin?

According to its product label, thymosin alpha-1 has a serum half-life of about 2 hours after subcutaneous administration. No pharmacokinetic data have been published for thymalin.

Are thymalin and thymosin alpha-1 approved medicines?

Thymalfasin is approved in more than 35 countries, and thymalin is registered in Russia. Neither is approved by the US FDA or the EMA. The products Helica Labs supplies are research chemicals for laboratory use only.

Is thymosin alpha-1 related to TB-500?

Only by name. TB-500 is based on thymosin beta-4, a different peptide with a different structure and function.

Peptide comparison

Thymalin vs Thymosin Alpha-1

Both come from research on the thymus, but they are very different products. Thymalin is a mixture of short peptides extracted from calf thymus. Thymosin alpha-1 is one defined peptide of 28 amino acids, made by chemical synthesis and known by its international non-proprietary name (INN), thymalfasin.

Reviewed by the Helica Labs research team · Last updated October 10, 2026

Longevity

Thymalin

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Longevity

Thymosin Alpha-1

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Thymalin vs Thymosin Alpha-1
	Thymalin	Thymosin Alpha-1
What it is	Thymalin A polypeptide extract of calf (bovine) thymus, registered in Russia as a prescription immunomodulator.	Thymosin Alpha-1 A single peptide first isolated from thymosin fraction 5, a calf thymus extract. Today it is made by chemical synthesis; INN thymalfasin.
Sequence and composition	Thymalin A mixture, not one defined sequence. The developers propose short peptides such as Lys-Glu and Glu-Trp as its active components. The Russian medicine contains glycine as an excipient; research-grade vials may differ.	Thymosin Alpha-1 Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn: 28 amino acids, acetylated at the N-terminus. It is the N-terminal part of the protein prothymosin alpha.
Structure and mass	Thymalin No single molecular mass: a mixture of low-molecular-weight peptides.	Thymosin Alpha-1 C129H215N33O55, about 3,108 Da.
Proposed mechanism	Thymalin Proposed to support T-cell maturation and immune balance. In cell studies, thymalin and its proposed dipeptides lowered the inflammatory cytokines IL-1β, IL-6 and TNF-α.	Thymosin Alpha-1 Acts on both innate and adaptive immunity, including Toll-like receptor signalling in dendritic cells, T-cell maturation and natural killer cell activity.
Half-life	Thymalin Not established. No human pharmacokinetic study of the extract or its proposed peptides has been published.	Thymosin Alpha-1 About 2 hours after subcutaneous administration, according to the product label; serum levels return to baseline within 24 hours.
Evidence in humans	Thymalin Clinical studies come almost entirely from one Russian research network, including two small randomised trials in hospitalised COVID-19 patients in 2021. Not replicated independently.	Thymosin Alpha-1 Many clinical trials over several decades; approved uses include chronic hepatitis B. The large phase 3 TESTS trial in sepsis (2025, 1,089 patients analysed) found no 28-day mortality benefit.
Regulatory status	Thymalin Registered as a prescription medicine in Russia and some other CIS countries. Not approved by the FDA or the EMA.	Thymosin Alpha-1 Thymalfasin is approved as a medicine in more than 35 countries (2009 review), but not by the FDA or through the EMA's centralised procedure.

Key differences

Extract versus defined molecule: thymalin is a mixture whose make-up depends on the extraction, while thymosin alpha-1 is one synthetic peptide with a fixed sequence and mass.
Thymosin alpha-1 has a measured half-life of about 2 hours; thymalin does not have one.
The evidence differs in scale. Thymalfasin has been tested in international trials, including a large sepsis trial in 2025 that found no mortality benefit. Thymalin's data come from one research network.
Both have national approvals, in different countries. Neither is approved by the FDA or the EMA.
Neither is related to TB-500, which is based on thymosin beta-4, a different thymic peptide.

For research use only. Not for human consumption. Always verify against current literature.

Frequently asked questions

What is the difference between thymalin and thymosin alpha-1?: Thymalin is an extract of calf thymus containing a mixture of short peptides. Thymosin alpha-1 (thymalfasin) is a single synthetic peptide of 28 amino acids with a defined sequence. Both are studied as immune modulators, but their composition, evidence and approval status differ.
Is thymalfasin the same as thymosin alpha-1?: Yes. Thymalfasin is the international non-proprietary name (INN) for synthetic thymosin alpha-1, which has the same sequence as the natural peptide.
What is the half-life of thymosin alpha-1 and thymalin?: According to its product label, thymosin alpha-1 has a serum half-life of about 2 hours after subcutaneous administration. No pharmacokinetic data have been published for thymalin.
Are thymalin and thymosin alpha-1 approved medicines?: Thymalfasin is approved in more than 35 countries, and thymalin is registered in Russia. Neither is approved by the US FDA or the EMA. The products Helica Labs supplies are research chemicals for laboratory use only.
Is thymosin alpha-1 related to TB-500?: Only by name. TB-500 is based on thymosin beta-4, a different peptide with a different structure and function.

All peptide comparisons