Thymalin vs Thymosin Alpha-1: differences, evidence and safety

Answer first

Thymalin is a mixture of peptides extracted from the thymus glands of calves, approved in Russia and in no other market checked. Thymosin Alpha-1 is one fully synthetic peptide of 28 amino acids, a prescription medicine in Italy and China. No study comparing them directly could be found in the sources reviewed for this page.

At a glance

How they work

Both names point to the thymus, the gland in which T cells, a group of immune cells, mature. Both are described as acting on the immune system. Beyond that shared root, one is a mixture and the other a single molecule.

Thymalin

• It is an organ extract. Thymus glands of calves and young cattle are processed so that large proteins break down and fragments below 10 kDa survive ^[1], ^[2].
• No established mechanism could be found in the sources. The Russian label describes an effect, not how it comes about. It says the extract restores disturbed immune reactivity and regulates the number and ratio of T and B lymphocytes ^[2].
• Since around 2017 the developing group has proposed that short peptides in the extract bind to DNA and to histones in the cell nucleus. That idea was tested on two isolated dipeptides, not on the extract ^[3].
• In cultured human blood stem cells, two markers of immaturity (CD44 and CD117) fell two- to threefold. A marker of mature T cells (CD28) rose 6.8-fold ^[4].

Thymosin Alpha-1

• It is one peptide of 28 amino acids with an acetyl group capping one end. It matches a peptide first isolated from calf thymus in 1977, but the medicine is made entirely by chemical synthesis ^[5], ^[6].
• The American regulator names signalling through Toll-like receptors as the mechanism that is at least partly established. These are sensors on immune cells that recognise patterns characteristic of microbes ^[5].
• The Italian product information describes an effect on the development of T lymphocytes ^[7]. The peptide may also raise HLA-DR on monocytes, a marker of immune responsiveness that falls in severe illness ^[8].
• The regulator states that no relationship between amount and effect could be derived from the preclinical work ^[5].

The core difference is what is being given. Thymosin Alpha-1 has a sequence, a formula (C129H215N33O55) and a mass of 3108.3 ^[6]. Thymalin has none of these, because it is many peptides in proportions that depend on the batch ^[1]. Even the PubChem record found under its name describes thymulin, a different nine-unit peptide ^[9].

Evidence about a defined molecule does not transfer to a mixture, so results for one say nothing about the other, in either direction ^[6], ^[1].

What is known about their time in the body differs too. In a study of nine healthy volunteers, Thymosin Alpha-1 peaked one to two hours after an injection under the skin. Its half-life was under three hours ^[10].

The Italian product information gives the peak at six hours ^[7]. The Russian label for Thymalin has no section on absorption or elimination ^[2].

What the studies show

No study that compares Thymalin and Thymosin Alpha-1 directly could be found in the published record reviewed for this page. Neither source monograph cites a trial in which both appear. What follows are the separate studies of each substance.

How much research could be found

Literature count A PubMed search on 17 September 2026 returned 293 records for Thymalin. Of these, 254 are in Russian and 30 in English, and 100 name one of its two developers as an author ^[11]. The main public trial register returned no entry for it, while a control query returned 426 ^[12].

Register count The same register held 64 entries for Thymosin Alpha-1 in September 2026, about five sixths of them from Chinese sponsors ^[13]. A Cochrane review, a formal pooling of randomised trials, covered its use in hepatitis B in September 2026 ^[14].

Thymalin: the longevity study

Controlled clinical study The claim that Thymalin extends life rests on one paper. It appeared in Russian in 2002 and in English in 2003, with the same data ^[15], ^[1]. Its St Petersburg arm divided 94 women aged 66 to 94 into four groups of 22 to 24. They received placebo, Thymalin, the pineal preparation epithalamin, or both together ^[1].

The paper measured 44 parameters without correcting for multiple testing, gave no confidence intervals and set no primary endpoint in advance. It carries no ethics, funding or competing-interest statement, and its authors developed the substance ^[1].

Not randomised The most quoted figure comes from a separate group of 20 people, given Thymalin together with epithalamin every year for six years. Anyone still treated in the sixth year has necessarily survived six years. This distortion, called immortal time bias, makes a treatment look protective ^[1].

Thymosin Alpha-1: sepsis and pancreatitis

Phase 3 RCT The largest trial recruited 1106 adults with sepsis, a life-threatening reaction to infection, across 22 Chinese centres between 2016 and 2020. It was double-blind and placebo-controlled. The authors found no clear evidence that the peptide reduced death from any cause within 28 days, the primary endpoint ^[16].

RCT An earlier trial by the same group, with 361 patients, is the one usually cited as positive. It was only single-blind, had no placebo, and its main statistical test did not reach significance ^[8].

Meta-analysis A 2025 review pooled 11 randomised trials with 1927 participants. The pooled effect shrank and lost significance once the analysis was restricted to the higher-quality trials ^[17].

RCT A double-blind, placebo-controlled trial enrolled 508 patients with predicted severe necrotising pancreatitis, an inflammation in which pancreatic tissue dies. It ran in 16 Chinese hospitals. Treatment did not reduce infection of the dead tissue during the admission, the primary endpoint ^[18].

Thymosin Alpha-1: hepatitis B and C

Cochrane review The September 2026 review pooled ten randomised trials with 1349 participants with chronic hepatitis B. The reviewers were not sure whether treatment reduces death or serious harms. They rated the certainty of the evidence very low for every outcome but one, where it was low ^[14].

Phase 3 RCT The best-designed single trial in hepatitis B was double-blind and placebo-controlled, with 97 patients. Its authors wrote that their results did not confirm the effects reported in other clinical studies ^[19].

RCT A trial enrolled 552 people with hepatitis C who had not responded to standard antiviral treatment. Adding the peptide did not meet the primary endpoint ^[20].

Thymosin Alpha-1: the one licensed use

Pilot study The Italian licence covers boosting the response to influenza vaccination in people with weakened immune defences ^[7]. Its evidence is a pilot study in dialysis patients, 99 in the safety population, in three groups without placebo. Antibody levels were higher in the treated groups at day 21, and had fallen further by day 42 ^[21].

Regulatory assessment The American regulator reviewed five vaccine studies from 1986 to 2012, two of them only conference abstracts. It found the evidence insufficient to reach any conclusion ^[5].

COVID-19: the one illness studied for both

Randomised, single-blind In 2020 a single-centre trial gave Thymalin or saline to 80 patients in hospital with severe COVID-19. It missed both endpoints it had named as primary. These were time to clinical improvement (p = 0.41) and a lung imaging result at day 14 (p = 0.43) ^[22].

The groups did not start level. Invasive ventilation was in place for 45.4 per cent of the control group against 25 per cent of the treated group (p = 0.06). A register query found no entry for the trial ^[22], ^[12].

Meta-analysis For Thymosin Alpha-1, the regulator examined four pooled analyses. Three found no reduction in deaths. Even the positive one found no difference in the need for mechanical ventilation or in length of hospital stay ^[5], ^[23].

RCT An American trial in 194 dialysis patients compared the peptide with an untreated group, without blinding or placebo. Only an interim report could be found, and the efficacy endpoints were not analysed in it ^[24].

These results come from different illnesses, populations, endpoints and study lengths. The figures for Thymalin and Thymosin Alpha-1 therefore cannot be set against each other.

Safety

For neither substance could a modern safety profile with measured frequencies be found. The two records differ mainly in where the gaps lie.

Thymalin, from the Russian label and the published work:

• Allergic reactions are the only adverse effect the label lists, with no frequency given ^[2].
• Three contraindications are stated: individual hypersensitivity, pregnancy and breastfeeding. The label has no section on interactions with other medicines ^[2].
• Material of animal origin may carry prions, infectious agents or nucleic acids. The developers name this risk themselves. Their reassurance comes from the manufacturing side ^[1].
• The phrase "practically no side effects" comes from a review by the developing group. It summarises impressions, not collected safety data ^[25].
• The American regulator named the product in a 2024 warning letter. It was particularly concerned that the product was marketed for use in children ^[26].

Thymosin Alpha-1, from the Italian product information and the American assessment:

• Injection-site discomfort is the commonest reported effect, described as occasional, mild and transient ^[7], ^[5].
• Rises in a liver enzyme were reported in people with chronic hepatitis B, and thyroid hormone values shifted in hepatitis C studies ^[5].
• A fatal immune-driven anaemia and a graft failure were reported in stem cell transplant recipients. The regulator warns that an immune stimulant could cause or worsen graft-versus-host disease in that group ^[5].
• Antibody formation may pose a significant risk, according to the regulator, although human data on it are lacking ^[5].
• The Italian licence rules it out in pregnancy and breastfeeding, and in children and adolescents ^[7].
• Animal studies at the highest level tested showed falls in white cells and platelets with repeated administration ^[7].

For both, the sources name the same weak point outside the registered products. Grey-market Thymalin sits outside any pharmaceutical quality system ^[26]. For Thymosin Alpha-1, the regulator notes there are no safety data at all on compounded preparations ^[5].

Why this page lists no doses. Both are prescription-only medicines where they are approved, Thymalin in Russia and Thymosin Alpha-1 in Italy and China. Choosing an amount is a matter for a prescriber and valid product information. This page therefore reports what the studies measured without repeating the amounts they used.

Legal status

Thymalin has been approved in Russia since a Soviet order of 10 November 1982, prescription-only; its current registration dates from 21 June 2024 ^[1], ^[27]. No authorisation was found in the United States, the European Union, Germany, Canada or Switzerland ^[28], ^[29]. The British and Australian registers could not be read. Thymosin Alpha-1 has been prescription-only in Italy since 27 April 1993 and is registered in China until May 2027 ^[30], ^[31]. It is not approved in the United States, where an advisory committee voted 4 to 17 against its use in pharmacy compounding ^[32]. Neither is on the 2026 prohibited list; its only thymosin entry, under S2.3, is thymosin beta-4 ^[33]. Status: 17 September 2026.

Used together?

The blend directory lists no product that contains Thymalin or Thymosin Alpha-1. The full list is under blends.

No study of Thymalin and Thymosin Alpha-1 given together could be found in the sources reviewed for this page. No information on what the combination does or how safe it is could be found in them. The Italian product information for Thymosin Alpha-1 advises caution when it is used alongside other immunomodulating medicines ^[7].

Frequently asked questions

Which is better, Thymalin or Thymosin Alpha-1?

Neither can be ranked, because no study comparing them could be found in the sources reviewed for this page. Thymosin Alpha-1 has large randomised trials, but the three largest, in sepsis, pancreatitis and hepatitis C, missed their primary endpoints. Thymalin's best-known evidence is a small, unregistered study by its developers, and its one hospital trial missed its primary endpoints too.

Is Thymalin or Thymosin Alpha-1 safer?

No comparison of their safety could be found, so no ranking is possible. The Thymalin label lists only allergic reactions, without a frequency. For Thymosin Alpha-1 the American regulator describes injection-site discomfort, liver enzyme rises and serious events in stem cell transplant recipients. For neither could a modern safety profile with measured frequencies be found.

What is the difference between Thymalin and Thymosin Alpha-1?

Thymalin is a mixture of peptides extracted from the thymus glands of calves, with no sequence, formula or mass. Thymosin Alpha-1 is one synthetic peptide of 28 amino acids, with the international name thymalfasin and the WHO code L03AX25. Approvals could be confirmed in Russia for Thymalin and in Italy and China for Thymosin Alpha-1, and in no other market checked.

Can Thymalin and Thymosin Alpha-1 be taken together?

No study of the two given together could be found in the sources reviewed for this page. No data on the effect or the safety of the combination could therefore be found. The blend directory lists no product containing either. The Italian product information for Thymosin Alpha-1 advises caution alongside other immunomodulating medicines.

Is Thymalin the Russian version of Thymosin Alpha-1?

No. Both trace back to calf thymus, but Thymosin Alpha-1 was isolated from it in 1977 and is now made by chemical synthesis. Thymalin is still extracted from the gland and remains a mixture. Results for one cannot be carried over to the other, in either direction.

Where are Thymalin and Thymosin Alpha-1 approved?

Thymalin is a prescription-only medicine in Russia, where the current registration dates from 21 June 2024. Thymosin Alpha-1 is prescription-only in Italy, licensed on 27 April 1993 as an adjuvant to influenza vaccination, and registered as an import in China. The figure of thirty-plus approving countries comes from a company report that the American regulator could not verify.

Are Thymalin and Thymosin Alpha-1 banned in sport?

Neither is named on the 2026 prohibited list, whose only thymosin entry is thymosin beta-4, sold as TB-500. The catch-all class for unapproved substances does not cover Thymosin Alpha-1, because Italy and China have approved it. Absence from the list is not a clearance, since unapproved preparations still carry a contamination risk.

Were Thymalin and Thymosin Alpha-1 both tested in COVID-19?

Yes, but separately. A single-centre Thymalin trial in 80 hospital patients missed both of its primary endpoints (p = 0.41 and p = 0.43). For Thymosin Alpha-1, three of four pooled analyses found no reduction in deaths, according to the American regulator. No trial testing the two against each other could be found.

How long do Thymalin and Thymosin Alpha-1 stay in the body?

For Thymosin Alpha-1, a study in nine healthy volunteers found a half-life under three hours, with the peak level one to two hours after injection. For Thymalin, the Russian label has no section on absorption or elimination. No such data could be found in the sources reviewed for this page.