Thymosin Alpha-1: The Approval and the Evidence Are for Different Things
The only European registration I could verify is Italian, and its indication section is one sentence about influenza vaccination in immunocompromised patients. The two largest placebo controlled trials I found, in sepsis and in hepatitis C, both came back null.
What it is
Thymosin alpha-1, generic name thymalfasin, is a chain of 28 amino acids with an acetyl group capping one end. FDA's chemistry review prints the whole sequence and a molecular weight of 3,108.3 g/mol, so unlike Cerebrolysin this is a molecule a laboratory report has something definite to check against.
The origin is what the marketing leans on. FDA says the peptide was "originally isolated from thymosin fraction-5 of calf thymus in 1977", and fraction 5 is a partially purified calf thymus extract, "a family of at least 40 mostly small acidic polypeptides" in the words of the researcher who named it. The founding clinical work of the field, a first investigational new drug approval in 1974 and a 1975 New England Journal of Medicine paper in children with primary immunodeficiency, used that extract. Epithalon has the same shape and never recovered from it. Thymosin alpha-1 did, building a large literature under its own name, so a page citing decades of thymosin research is usually pointing at the extract while the trials below really are about the peptide.
What the trials found
TESTS, published in the BMJ in 2025, randomised 1,106 adults aged 18 to 85 with sepsis across 22 centres in China, double blinded, 552 to 1.6 mg of freeze dried thymosin alpha-1 injected under the skin every 12 hours for seven days and 554 to freeze dried saline given the same way. Among the 1,089 analysed, the primary endpoint, death from any cause within 28 days, occurred in 127 of 542 on the drug, 23.4 percent, against 132 of 547 on placebo, 24.1 percent. The trial "found no clear evidence to suggest that thymosin α1 decreases 28 day all cause mortality in adults with sepsis". SciClone Pharmaceuticals, the company behind the Italian product, part funded it, which makes a null result harder to set aside rather than easier. One warning before you go and check: the BMJ corrected the paper in place in May 2025, and the PubMed abstract still prints the old hazard ratio of 0.99 rather than the corrected 0.97.
The prespecified subgroup, a split planned before anyone saw the results, appears on no sales page I read. In patients under 60 the hazard ratio was 1.67 across 1.04 to 2.67, against 0.81 across 0.61 to 1.09 in patients aged 60 and over, a gap between the age groups that would arrive by chance about once in a hundred runs, and above 1 means more deaths on the drug. Adjusting for organ support given before randomisation pulls the under 60 figure to 1.45 across 0.89 to 2.36, which no longer excludes no effect. The authors describe it as a potential differential effect based on age. Read one way that is older patients benefiting more. Read the other, the younger arm did worse.
An earlier single blind trial from the same lead author split 361 patients 181 to the drug and 180 to control and reported 26.0 percent deaths against 35.0, a gap whose own range of uncertainty, 0.54 to 1.02, still includes no effect at all, and whose two P values fall on opposite sides of the conventional line at 0.062 and 0.049. Its abstract states neither the dose nor the route. The immune marker it found improving, monocyte HLA-DR, sat under exploratory outcomes in TESTS and did not move there.
A 2025 meta-analysis pooling eleven sepsis trials, 967 patients on the drug against 960 on control, does report a benefit, odds ratio 0.73 across 0.59 to 0.90. Two of its own subgroups undo it: restricted to the higher quality trials the figure is 0.82 across 0.65 to 1.03, and restricted to multicentre trials 0.86 across 0.68 to 1.08, both of which include no effect, and the authors' own sequential analysis calls the accumulated sample size inadequate.
Hepatitis is the record the sales copy actually cites, and it is the cleaner failure of the two. Ciancio and colleagues randomised 552 patients whose hepatitis C had not responded to standard treatment, 275 to 1.6 mg under the skin twice weekly on top of the standard two drug hepatitis C treatment of the time, pegylated interferon and ribavirin, and 277 to placebo on top of the same, for 48 weeks. Cure rates were 12.7 against 10.5 percent. "Thymosin alpha-1 seems to play no role in the primary therapy of the disease", the authors wrote, and their final sentence raises "the hypothesis that thymosin alpha-1 may have a secondary therapeutic role as an adjuvant in the prevention of relapses", which rests on a subgroup rather than on everyone randomised: 34 of 83 against 26 of 99, that is 83 of the 275 randomised to the drug and 99 of the 277 randomised to placebo.
In hepatitis B, Mutchnick and colleagues gave 1.6 mg under the skin twice weekly for six months to 49 patients against 48 on placebo, saw a complete response in 7 against 2, and closed that the results "do not confirm observations of treatment efficacy reported in other clinical studies". FDA's read of the whole hepatitis B file is "insufficient evidence to determine the effectiveness of Ta1", and what does the damage is not the trials: approved antivirals drive the virus to undetectable in 68 to 90 percent of patients after 48 weeks of therapy.
The use that is actually registered
Section 4.1 of the Italian summary of product characteristics is one sentence, and here it is entire: "ZADAXIN è un adiuvante della vaccinazione anti-influenzale in soggetti immunocompromessi." Zadaxin is an adjuvant to influenza vaccination in immunocompromised subjects. Not hepatitis B, which is what the sales copy cites. Not immune support, which is what it is sold for. The schedule beneath it is one vial into a muscle or under the skin twice weekly for four weeks from the first vaccination, repeated from week eight to week twelve for the second.
Now look at what sits under that sentence. Gravenstein and colleagues, Journal of the American Geriatrics Society, 1989: 90 men aged 65 to 99, mean age 77.3, randomised double blind between thymosin alpha-1 at 900 micrograms per square metre of body surface area under the skin twice weekly for eight doses and placebo on the same schedule, alongside the 1986 influenza vaccine. What was measured was antibody in a laboratory assay, in the 85 men whose blood was usable. Not whether anybody caught influenza.
FDA reviewed five vaccine adjuvant studies in December 2024 and found a "lack of sufficient evidence to determine any conclusion on the effectiveness of Ta1 as a vaccine adjuvant". Four of the five used that assay, which FDA says "is not a measure of clinical effectiveness", two existed only as conference abstracts, and control groups were missing or inadequate. So the American regulator read five studies of the use Italy registered and called the evidence insufficient to reach any conclusion. I could not find the Italian assessment report, so what Italy weighed and what FDA weighed cannot be compared directly here. That is the weld: a real registration document fixed to a real trial literature about other diseases.
Whose evidence it is
Every trial above enrolled people already ill or defined by a condition, and I could not find a completed randomised trial in healthy adults for immune support, infection prevention or anything resembling longevity. Two things sit close to that line and should be named. Rost and colleagues gave nine healthy volunteers 900 micrograms per square metre under the skin in 1999, but measured blood concentrations and nothing else. And NCT06821100, a randomised open label first stage study aiming to enrol 75 adults aged 65 and over receiving a covid booster, began recruiting in December 2024 and excludes anyone moderately or severely immunocompromised, but it is still recruiting and has posted no results. The nearest completed prevention study is in a very unhealthy group: 91 dialysis patients given 1.6 mg under the skin twice weekly for eight weeks against 98 on standard care, 5 covid infections against 7, 3 deaths against 7, no analyses posted.
Then the ageing premise, which is the load bearing transfer. The pitch is that the thymus shrinks with age, so its hormone falls, so replacing it restores immunity. Weller and colleagues measured serum thymosin alpha-1 in 681 healthy adults aged 18 to 101 and reported "no differences in the levels when analyzed according to race, sex or age". And the two researchers who built the vaccine adjuvant case opened their 2007 review with "the immune deficiency of aging (immune senescence) is not profound. In fact, it may be of little clinical consequence." Their next sentence belongs with it: "However, older people are prone to chronic and debilitating disorders which alone, or in concert with the medications used in their treatment, may add to the age effect and create a more clinically relevant immune deficiency." They are not undercutting themselves. They are saying that ageing on its own is not the problem, which is a problem for anybody selling this to a healthy person on the strength of a birthday.
Where the 1.6 mg came from
Section 4.2 of the Italian label sets the dose at 900 micrograms per square metre of body surface area, then prints a table of heights, weights, surface areas and doses so a prescriber can choose between the 1.6 mg and 2 mg vials. Every row of that table is 900 micrograms multiplied by the patient's surface area, to the nearest 10 micrograms.
| Patient on the label's table | Body surface area | Dose the label prints | 900 mcg times that area |
|---|---|---|---|
| Man, 175 cm | 1.83 m² | 1.65 mg | 1.647 mg |
| Man, 190 cm | 2.08 m² | 1.87 mg | 1.872 mg |
| Woman, 155 cm | 1.47 m² | 1.32 mg | 1.323 mg |
So 1.6 mg is not a decision about how much drug a person needs. It is an average adult multiplied by 900 and rounded to the vial on the shelf, the way shoes come in whole sizes because that is what the shop stocks and not because feet do. One line of the same section does not add up, and this reading is mine: it calls 900 micrograms per square metre the weekly dosage, while the table computes that figure as a single injection and the schedule gives two injections a week.
Where the 900 itself came from I could not establish. It is the dose in the 1989 influenza trial and in the 1999 pharmacokinetic study, and FDA's table of vaccine adjuvant studies records it in use as early as a 1986 pilot in nine subjects that exists only as a conference abstract. The trail ends there.
FDA records daily doses across the literature of roughly 1 to 16 mg and records 1.6 mg as the commonest dose in clinical studies, so the fixed number that circulates sits near the bottom of the range, and it is the vial size the hepatitis regimens were written around. I tried to read the dosage chart on one vendor page that circulates and could not confirm a single figure in it, because the numbers are drawn by the browser rather than sent by the server. From the published side: every trial in this entry dosed continuously, and I found no published evaluation of cycling this compound.
What the regulators have on file
The United States: not approved, for anything. An FDA reviewer said so on the record in December 2024, "any products containing thymosin alpha-1 are not approved in the United States by FDA", and a second reviewer, asked whether an application was ever filed, said "we don't have approval for Ta1 for any condition". FDA's slides note that a website advertises a compounded injectable product as "FDA-approved" and answer it in the same breath: "FDA has approved no drug products containing Ta1".
On 4 December 2024 the Pharmacy Compounding Advisory Committee was asked whether thymosin alpha-1 free base should join the list of substances American pharmacies may compound with, and voted 4 yes, 17 no, no abstentions, then returned the identical tally on the acetate salt. Free base and acetate are the two forms the raw powder is sold in, the same peptide packaged with a different partner, and they dissolve to different strengths. The nomination that triggered the review had already been withdrawn by the pharmacy network that filed it, and FDA evaluated the substances anyway. The vote is a recommendation rather than the end of it, since 21 CFR 216.23 lists six substances that may be used in this kind of compounding and four that may not, and thymosin alpha-1 is on neither list.
The claim that it is approved across the Asia-Pacific region, Latin America, Eastern Europe and the Middle East traces to SciClone Pharmaceuticals' 2014 annual report, and FDA's answer is one sentence: "FDA is unable to independently verify these claims of approval in all the specified countries." It adds that the drug "is not approved in the United States, Japan, or Europe (except Italy)" and is not recognised in the European or Japanese pharmacopoeias. Health Canada's database returned nothing for thymalfasin, and the Chinese pages describing an imported registration contradicted each other on the route of injection, so I am carrying that one as secondary and unconfirmed.
What could go wrong
Start with what is reassuring, because it is. FDA concluded that in most clinical studies the peptide "has not been associated with significant adverse events attributable to Ta1" at 1 to 16 mg under the skin for up to twelve months, the commonest reaction being irritation where the needle went in, and the sepsis trial found adverse events in 66.4 percent of the 542 patients on the drug against 67.6 percent of the 547 on placebo.
The specific harms are about who is taking it. In Perruccio and colleagues' study of stem cell transplant recipients, six had a haploidentical transplant, meaning from a half matched donor, and of those six, five were alive and disease free at a median of 10 months while one developed fatal immune haemolytic anaemia, in which the immune system destroys the person's own red blood cells. FDA describes that study as 8 sibling matched and 6 haploidentical recipients given 1.6 mg daily under the skin for 16 weeks, and warns that stimulating immunity in someone whose immunity is being deliberately suppressed "could cause or worsen acute or chronic graft-vs-host disease and lead to engraftment failure". It raises the same caution about the Italian indication itself: "Adding an immunomodulatory product such as Ta1 to any vaccine could pose unknown safety concerns that warrant further evaluation." The label rules the product out in pregnancy, breastfeeding and children, and says autoimmune disease must be assessed case by case.
Then the vial. FDA's chemists called both the free base and the acetate salt "not well-characterized", with data missing on impurities, aggregates and endotoxin, and flagged that a peptide injected under the skin can provoke antibodies against itself. The compounding nomination proposed 3 mg per millilitre when the free base dissolves in water only up to 2 and the acetate only up to 1, and no information was provided about how the higher concentration is achieved.
What nobody knows
Whether the approved use is supported. Italy registered it as a flu vaccine adjuvant, FDA reviewed five studies of exactly that and said the evidence was not enough to reach a conclusion, and I found no modern trial that retested either position.
Whether the age subgroup means anything. A split by age after a null primary result is a hypothesis, including the half that points the wrong way.
Whether anything happens in a healthy person. The one randomised study I found in adults screened to be free of immune compromise is phase 1, unblinded, 75 people, still recruiting.
How it behaves in the body. Nine healthy volunteers gave a peak at one to two hours and a half life below three hours, while the Italian label says a peak at six hours. I could not reconcile the two.
What this adds up to
Thymosin alpha-1 is not a fake, and that is what makes it unusual here. There is a molecule you can draw, a real marketing authorisation, a 1,106 patient double blinded trial most compounds on this site would love to have, and a safety record that is genuinely boring. None of those things is attached to the others. The approval is one sentence about flu shots in immunocompromised patients. The trials are about sepsis and hepatitis, and the largest placebo controlled ones are null. Every piece is real. The picture assembled out of them is not.
The subgroup is the part that should not be left behind. In the largest blinded trial I found, in a split planned in advance rather than fished for afterwards, patients under 60 did worse on the drug. One subgroup after a null trial is a hypothesis and not proof of harm. But this peptide is sold to people younger and healthier than anyone it has been properly tested in, and the only signal in the record that speaks to age points straight at them, in the wrong direction.
If you have seen thymosin alpha-1 for sale, check which indication the vendor attached to the Italian approval. Every page I read named hepatitis. The label names influenza.
Frequently asked
Is thymosin alpha-1 approved?
In Italy, yes, and for one use only: section 4.1 of the Italian label is a single sentence naming it an adjuvant to influenza vaccination in immunocompromised subjects. FDA staff stated on the record in December 2024 that products containing thymosin alpha-1 are not approved in the United States for any condition. FDA also states it is not approved in Japan or in Europe outside Italy, and that it was unable to independently verify a company's claim of approval in all of the other countries that claim names.
Does thymosin alpha-1 work for sepsis?
The largest placebo controlled trial I found says it does not. TESTS randomised 1,106 adults with sepsis across 22 centres in China, double blinded, 552 to the drug injected under the skin every 12 hours for seven days and 554 to a freeze dried saline dummy. Deaths within 28 days were 23.4 percent on the drug against 24.1 percent on the dummy, and the authors wrote that they found no clear evidence it lowers 28 day deaths. A subgroup split by age, planned before the results came in, pointed the other way in patients under 60.
Does it help hepatitis B or hepatitis C?
The two placebo controlled trials I found came back null. In hepatitis B, 49 patients given 1.6 mg under the skin twice weekly for six months against 48 on placebo gave a complete response in 7 against 2, a gap a study that size could not separate from chance. In hepatitis C, 552 patients were randomised, 275 to the drug on top of standard treatment and 277 to placebo on top of the same, and cure rates were 12.7 against 10.5 percent. FDA concluded it has insufficient evidence in hepatitis B and insufficient data in hepatitis C. Tablets now cure more than 90 percent of hepatitis C in 8 to 12 weeks.
Where does the 1.6 mg figure come from?
From arithmetic on the Italian label, reported here as a label figure and not as a recommendation. Section 4.2 sets the dose at 900 micrograms per square metre of body surface area and prints a table of heights and surface areas, and every row of that table is that figure multiplied by the patient's surface area, to the nearest 10 micrograms. A man of 175 cm comes out at 1.65 mg and a woman of 155 cm at 1.32 mg, so 1.6 mg is an average adult rounded to a vial size. I could not find the study that derived the 900 in the first place.
Is thymosin alpha-1 safe?
The trial record is unremarkable and should be reported as such: FDA concluded that in most clinical studies it has not been associated with significant adverse events attributable to the drug at 1 to 16 mg under the skin for up to twelve months, with injection site irritation the commonest complaint, and the sepsis trial found adverse events in 66.4 percent of 542 patients on the drug against 67.6 percent of 547 on placebo. The specific concerns are about who takes it. FDA warns it could cause or worsen graft versus host disease in stem cell transplant recipients, the Italian label rules it out in pregnancy, breastfeeding and children and says autoimmune disease must be assessed case by case, and FDA's chemists called the bulk substance offered to compounding pharmacies not well characterised, with impurity and aggregate data missing.
Does thymosin alpha-1 boost immunity in a healthy person?
I could not find a completed randomised trial that answers it. Every trial I found that measured whether people got better enrolled patients or people defined by a medical condition. The closest completed prevention study gave 1.6 mg under the skin to 91 dialysis patients twice weekly for eight weeks against 98 on standard care, and reported 5 covid infections against 7, 8 other infections against 6 and 3 deaths against 7, with no statistical analyses posted. One randomised open label study aiming to enrol 75 adults aged 65 and over receiving a covid booster began recruiting in December 2024 and has posted no results.
This content is for educational and informational purposes only and is not medical advice. Peptides discussed are research compounds and may not be approved for human use. Nothing here should be used to diagnose, treat, cure, or prevent any disease. Always consult a qualified healthcare professional before starting any peptide, supplement, or protocol. Individual responses vary. Do not self-administer compounds without proper medical supervision.
Get the next one in your inbox
Free. One email a week at most. Unsubscribe in one click.
Double opt-in · No spam · Unsubscribe anytime
More in Immune and thymic
- ARA-290 Has Real Randomised Trials, and Their Main Endpoint Was a Photograph of an EyeIts sequence does not appear in erythropoietin at all, which is the interesting part. Across a 1 mg to 8 mg range the response did not rise with the dose, the skin biopsy that diagnoses the disease did not move, and I found no trial registered anywhere after the 2017 announcement of progress.
- LL-37 Has a Human Dosing Record. I Found None of It Under the SkinThree randomised trials I found put it on a wound and one injected it into tumours. The largest missed its primary endpoint, its sponsor went into liquidation in October 2023, and the dose response ran backwards twice, the second time in a different molecule.
- Thymalin Is Calf Thymus Extract, and Its Clinical Record Is Being Lent Forward to Two Other PeptidesThe registered active substance is the words thymus extract, 10 mg from the glands of calves and cattle under one year. Khavinson's group now says the active substances are the dipeptides KE and EW, sold separately as Vilon and Thymogen. In the geroprotection paper everyone cites, 24 people received Thymalin on its own.