Peptide & Experimental
Thymosin Alpha-1 (TA1)
Immunomodulatory peptide (28 amino acids) · Zadaxin, thymalfasin
Thymosin Alpha-1 is an endogenous messenger of the thymus gland that controls the maturation and activation of T cells. Unlike most peptides in the biohacking scene, it is a real medicine: it is approved as Zadaxin in more than 30 countries. Today it is best studied as support for the immune system when illness or cancer treatment has depleted the immune cells.
In brief
Thymosin Alpha-1 is a 28-amino-acid peptide that the thymus produces itself and that acts as an immunomodulator: it helps weakened T cells get back on their feet without blindly revving up the immune defense. The most convincing clinical data come from cancer care, where it markedly cushioned the crash of immune cells during radiotherapy and chemotherapy. As a treatment for cancer itself it is not proven, and in a large sepsis trial it did not lower mortality. It is not approved in Germany, but is considered very well tolerated in studies.
What it is
Thymosin Alpha-1 comes from the thymus, the small gland behind the breastbone. There, T cells learn to distinguish pathogens from the body’s own tissue. The peptide is one of the messengers with which the thymus runs this school. It was discovered in the research group of Allan Goldstein, from the same line as Thymosin Beta-4.
As a medicine, the active substance is called thymalfasin; the best-known brand name is Zadaxin. It is approved in more than 30 countries, mainly for chronic hepatitis B and C, and in some countries also as support for the immune system. Thymosin Alpha-1 is thus backed by decades of clinical experience and is not a niche experiment.
How it is supposed to work
Its core talent is the T cell: it promotes T-cell maturation and activation and at the same time awakens natural killer cells and the sentinel cells of innate immunity. The term immunomodulator fits better than immune booster. If the immune defense is weakened, it helps it back up. If it is overreacting, it is supposed to balance it instead. The image of a conductor rather than an accelerator pedal describes this idea well.
For the longevity scene, the thymus is the real reason for the interest. It shrinks from puberty onward and, beyond the age of 50, has largely been replaced by fatty tissue in many people. Less thymus means fewer freshly trained T cells and fewer of the control signals to which Thymosin Alpha-1 belongs. Supplementing a declining endogenous signal is the approach behind it.
What it is used for
The most exciting application today lies in cancer care, with a clear division of roles. Thymosin Alpha-1 is not meant to cure cancer. Chemotherapy and radiotherapy, however, hit not only the tumor; they also set back the immune system, and lymphocytes often drop massively. This is exactly where the peptide comes in: it is meant to help rebuild the immune defense during and after treatment so that the body copes better with the therapy.
In biohacking practice, it is obtained as a research peptide via the gray market and, according to reports, used in a targeted way, for example during the infection season, when traveling or in stressful periods, as a course rather than continuously. That is reported practice, not proof of efficacy and not a recommendation.
What is well supported
Best supported is that Thymosin Alpha-1 supports the number of immune cells in people whose counts have collapsed due to illness or therapy. In lung cancer under chemoradiotherapy, a severe drop in lymphocytes occurred in 19.1 percent with Thymosin Alpha-1, compared with 62.1 percent in the comparison group. In an analysis of 48 cancer patients, the median T-cell count rose from 422.5 to 614.0 per microliter of blood after 7 days of pretreatment. Radiation-induced pneumonitis was also less frequent in two Chinese studies: in a retrospective analysis of 196 patients with lung cancer, grade 2 or higher occurred in 14.5 percent with longer administration, versus 35.4 percent without the peptide.
Then there is tolerability. In a large European melanoma trial, the peptide added to chemotherapy brought no additional toxicity, and in a placebo-controlled sepsis trial with 1,106 patients the safety endpoints did not differ from placebo.
What the studies show
Lung cancer under chemoradiotherapy (GASTO-1043, 2022)
In a phase 2 trial from China, 69 patients with locally advanced non-small cell lung cancer additionally received Thymosin Alpha-1 during and after chemoradiotherapy. They were compared with 69 retrospectively matched patients without the peptide. Radiation pneumonitis of grade 2 or higher occurred in 36.2 versus 53.6 percent, severe lymphopenia in 19.1 versus 62.1 percent. The primary endpoint was met, but the control group was not randomized.
Metastatic melanoma (Maio, 2010)
A large randomized trial from Europe with 488 patients tested Thymosin Alpha-1 in addition to dacarbazine, partly combined with interferon alfa; the control group received dacarbazine plus interferon alfa. The primary endpoint was best response at 12 months: in two thymosin groups there were 10 and 12 tumor responses, in the control group 4, and the endpoint was met in these groups. Median survival was 9.4 versus 6.6 months, narrowly not significant. No additional side effects occurred.
Severe COVID-19 (Liu, 2020)
In a retrospective analysis of 76 severely ill patients from 2 hospitals in Wuhan, mortality was 11.11 percent with Thymosin Alpha-1 and 30.00 percent without. The authors also showed that exhausted T cells recovered and T-cell counts rose again. Because treatment was not randomized, this is a strong signal but not proof. Larger retrospective studies contradict it: in 771 critically ill patients, administration was not associated with lower mortality, and in a cohort of 2,282 patients it was even associated with poorer recovery. A meta-analysis of 9 studies with 5,352 patients found no effect on mortality.
Sepsis (TESTS, 2025)
The largest placebo-controlled trial to date randomly assigned 1,106 adults with sepsis in 22 centers, double-blind, to Thymosin Alpha-1 or placebo for 7 days. After 28 days, 23.4 versus 24.1 percent had died; the primary endpoint was not met. An earlier, smaller, single-blind trial with 361 patients had shown 26.0 versus 35.0 percent, narrowly not statistically significant (p = 0.062).
Where the data stop
The cancer data are encouraging but narrow. A 2026 review found 26 clinical publications on Thymosin Alpha-1 as an adjunct to cancer therapy for the period from 2016 to March 2026, including exactly 1 randomized trial; 80.8 percent of them came from China, most of them retrospective or case reports. A large European approval trial is lacking. For hepatitis B, a 2026 Cochrane review with 10 trials rates the certainty of the evidence as very low.
For sepsis, the large phase 3 trial showed no survival benefit. And for the applications most often mentioned in the scene, there are no controlled human data: benefit for healthy people, fewer infections in athletes or a measurable rejuvenation of the aging immune system are plausible ideas, but not studied.
Status, approval and legal
Thymosin Alpha-1 is approved as a medicine in more than 30 countries, mainly for chronic hepatitis, in some cases as an immune adjuvant. There is no EU-wide approval, but there is a national one in Italy (since 1996, prescription-only). It is not approved in Germany or the US. In 2023 the FDA placed it in Category 2 (safety concerns) for compounding pharmacies; it now lists it as a withdrawn nomination (as of April 2026). What circulates in Germany is mostly research-grade product from the gray market whose purity and sterility nobody checks. Anyone competing in events with doping controls should ask the NADA about its status in advance. We do not give dosages for unapproved substances.
Safety
In studies, Thymosin Alpha-1 is considered very well tolerated; the most likely effect is a mild reaction at the injection site. Added to chemotherapy, it brought no additional toxicity. Caution applies in autoimmune diseases and in combination with immunotherapies such as checkpoint inhibitors: one case of severe immune reactions affecting several organs under such a combination has been described, without the peptide being proven as the cause. Anyone undergoing cancer treatment should discuss any addition with the treatment team beforehand.
BK-Score Supported, with caveats
| Human evidence | 7 | |
|---|---|---|
| Mechanism | 7 | |
| Safety data | 7 | |
| Hype gap | 3 | |
| Track record of use | 6 |
The best-supported immune peptide among the research peptides: approved as thymalfasin in more than 30 countries, mainly for chronic hepatitis. The data are strongest on immune support in cancer care: in the phase 2 trial GASTO-1043, severe lymphopenia under chemoradiotherapy fell to 19.1 versus 62.1 percent, and in a randomized melanoma trial with 488 patients there were more tumor responses without additional toxicity. The large placebo-controlled sepsis trial TESTS (BMJ 2025, 1,106 patients), by contrast, found no survival benefit (23.4 vs. 24.1 percent), and the earlier ETASS trial (Critical Care 2013) was only borderline. The oncology literature published since 2016 is predominantly retrospective and 80.8 percent Chinese; the 2026 Cochrane review on hepatitis B rates the evidence as very low. The safety data are good thanks to placebo-controlled trials and long-standing approval. There is no EU-wide approval, but there is a national one in Italy; it is not approved in Germany; marketing it as a general immune super-peptide for healthy people goes beyond the indications that have been tested.
The score rates the state of knowledge, not the substance. “Safety data 9” means well studied – not harmless.
Subjective assessment by Biohacking Kompakt based on published scoring rules – not a scientific rating and not a medical recommendation. Rules and all ratings (German)
Frequently asked questions about Thymosin Alpha-1 (TA1)
What is Thymosin Alpha-1?
A 28-amino-acid peptide that the thymus gland produces itself. It controls the maturation and activation of T cells and acts as an immunomodulator. As a medicine it is called thymalfasin or Zadaxin.
Does Thymosin Alpha-1 help against cancer?
As a treatment against the tumor itself, it is not proven. It is studied as an adjunct meant to support the immune system during chemotherapy and radiotherapy. There, mainly Chinese studies show fewer severe drops in immune cells.
Is Thymosin Alpha-1 approved in Germany?
No. It is approved in more than 30 other countries, mainly for chronic hepatitis; in the EU there is no EU-wide approval, but there is a national one in Italy. In Germany it is only available as research-grade product from the gray market, whose quality is unverified.
What side effects does Thymosin Alpha-1 have?
In studies it is considered very well tolerated; the most common effect is a mild reaction at the injection site. Caution applies in autoimmune diseases and in combination with immunotherapies. This should be discussed with a doctor beforehand.
What is the difference from Thymosin Beta-4?
Both come from the same line of research but have different tasks. Thymosin Alpha-1 is the immune specialist; Thymosin Beta-4 is mainly associated with tissue repair. Only Thymosin Alpha-1 is approved as a medicine anywhere.
Does Thymosin Alpha-1 help against the aging of the immune system?
The idea is plausible because the thymus shrinks over the years and produces fewer control signals. So far, however, there are no controlled studies in healthy older people showing a benefit.
The podcast episode (in German)
Episode 7
AI podcast: Thymosin Alpha-1 – the immune peptide with an approval
The podcast by Paul Höser (Episode 7) · with Paul & Paula. Fresh, positive AI dialogue episode about Thymosin Alpha-1, the “conductor” of the immune system: an endogenous thymus peptide that lets T cells mature and brings the immune defense into balance. Approved as Zadaxin in more than 30 countries; in a small retrospective COVID analysis (Liu et al., Clin Infect Dis 2020) associated with lower mortality, larger studies found no benefit. Longevity angle: thymus shrinkage and immunosenescence. Information only, no dosage or usage recommendation.
Related
- Related topicTB-500 (thymosin beta-4 fragment)
- Same sectionLL-37
Sources
- Liu F et al., Int J Radiat Oncol Biol Phys 2022 (GASTO-1043)
- Maio M et al., J Clin Oncol 2010
- Xu M et al., Cancer Manag Res 2025
- Zhang HT et al., Transl Lung Cancer Res 2025
- Liu Y et al., Clin Infect Dis 2020
- Wu J et al., BMJ 2025 (TESTS)
- Wu J et al., Crit Care 2013 (ETASS)
- Naing C et al., Cochrane Database Syst Rev 2026
- Kim SD et al., Pharmaceuticals 2026 (scoping review)
- Dinetz E, Lee E, Altern Ther Health Med 2024
Open in the database – with search, filters and comparison (German app)
Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-10-04.