Thymosin Alpha-1 Peptide: Benefits and Safety

In the United States alone, it’s estimated that 15 million people have one or more autoimmune diseases,1 3.3 million have chronic viral hepatitis,2 and roughly 110 million adults have systemic inflammation.3 While these may seem like unrelated statistics, they’re all health conditions that the peptide thymosin alpha-1 (also called TA-1) might be able to help with, according to current research.

Beyond those mentioned above, TA-1 may promote better outcomes for a wide variety of health concerns due to the peptide’s potential to modulate the immune system. From cancer and Lyme disease to sepsis and even allergies, TA-1 has an impressive collection of purported applications — but does the science back them up?

In this guide, we’ll explore everything you need to know about thymosin alpha-1, including its history, efficacy, safety, uses, and what to expect when taking it.

Over the past two decades, Innerbody Research has helped tens of millions of readers make more informed decisions involving staying healthy and living healthier lifestyles.

All told, our team has dedicated well over a thousand hours throughout the past few years to researching a collection of promising peptides, including the thymosins. For our guide to thymosin alpha-1 alone, we spent 30+ hours poring over dozens of pieces of scientific literature on the peptide’s history, safety, uses, and more. We also gleaned valuable insights from health professionals with experience prescribing it to patients. Furthermore, a member of our team has undergone peptide therapy, meaning we’re able to share firsthand details of the patient experience.

Additionally, like all health-related content on this website, this review was thoroughly vetted by one or more members of our Medical Review Board for accuracy.

First described and characterized by biochemistry and immunology specialist Dr. Allan L. Goldstein in 1972, thymosin alpha-1 (TA-1) is a 28-amino-acid peptide of the thymosin family.4

Thymosins are hormone-like peptides produced by the thymus (a small, two-lobed gland that sits behind your sternum and just above your heart) that can influence various immune and nonimmune bodily processes.5 6 TA-1 mainly affects the former, with researchers stating that the peptide “has long been recognized for modifying, enhancing, and restoring immune function.”7 It does this primarily by influencing the production and activity of the body’s T cells (a type of white blood cell known as lymphocytes, which help fight infection and disease).7 8

In contrast, other thymosins have their own specialities, so to speak. For example, research suggests that thymosin beta-4 (TB4) and its synthetic form, TB-500, are particularly good at repairing or regenerating muscle and other soft tissue.9 10

Though thymosins are substances naturally produced by the thymus gland, peptide therapy uses synthetic forms. In the case of thymosin alpha-1, the chemically synthesized version (identical to human TA-1) is called thymalfasin or Zadaxin.7 11 12

Zadaxin is the only FDA-approved thymosin-based drug. It’s used as a chemotherapy inducer and as a treatment for chronic hepatitis B and C.13 However, outside of the United States, thymalfasin is also approved as an immune response enhancer (among other things) in 35 countries in Latin America, Eastern Europe, the Middle East, and the Asia-Pacific region. 7 14

As we touched on earlier, the research-supported potential uses of thymosin alpha-1 largely involve the peptide’s effects on immune system function. The authors of a 2020 review state that TA-1 has been used “in the treatment of immunocompromised states and malignancies, as an enhancer of vaccine response, and as a means of curbing morbidity and mortality in sepsis and numerous infections.”7 However, these are only a select few possible ways that TA-1 may be able to support positive health outcomes. Besides its FDA-approved uses, there are a myriad of other reasons for which clinicians in the U.S. may prescribe off-label compounded TA-1 peptide therapy to their patients.

Below, we break down the research behind some of the most promising applications for TA-1 peptide therapy.

For most healthy adults who aren’t pregnant or breastfeeding, thymosin alpha-1 should be generally safe when used as directed by a prescribing clinician. However, it’s still worthwhile for us to discuss the data behind the safety of TA-1.

In an FDA Pharmacy Compounding Advisory Committee Meeting presentation focused on TA-1 from the end of 2024, the authors detailed the peptide’s nonclinical and clinical safety information.31

To summarize, the nonclinical findings include:31

• Acute toxicity: In rodents, a single subcutaneous injection of TA-1 (up to 20mg/kg) produced no drug-related adverse effects.
• Repeat-dose toxicity: Subcutaneous injections of TA-1 in mice, rats, and marmosets over 13 weeks (up to 6mg/kg per day) and 26 weeks (up to 1mg/kg per day) led to no drug-related adverse effects. Additionally, it’s noted that “based on body surface area, the highest tested [subcutaneous] dose (1 mg/kg/day) administered for the longest time (26 weeks) to mice, rats, and monkeys provides safety margins of ~3-fold, 6-fold, and 12-fold to the daily human [subcutaneous] dose of 1.6 mg, respectively.”
• Reproductive and developmental toxicity: SciClone Pharmaceuticals, a biopharmaceutical company, claims to have “successfully completed” adequate reproductive toxicology studies on the use of TA-1 in rodents, but the FDA notes that no published nonclinical studies with the data could be identified.
• Genotoxicity: Neither in vivo nor in vitro assays of TA-1 produced “genotoxicity signals.”
• Carcinogenicity: No nonclinical studies investigating TA-1 for this concern were identified.

Pivoting to the results of clinical research, the FDA details the following findings:31

• Most commonly reported adverse effects: Generally, the most common adverse effects from TA-1 in clinical studies are injection site discomfort, irritation, and redness.
• Other adverse effects reported in studies: In various studies, some of the notable adverse effects reported were ALT flares in subjects with chronic hepatitis B, TSH abnormalities in subjects with chronic hepatitis C, nipple pain, and fatal immune hemolytic anemia and engraftment failure in hematopoietic stem cell transplantation (HSCT) recipients. HSCT is an intense chemotherapy treatment for those with multiple sclerosis (MS), chronic or acute leukemia, lymphoma, and multiple myeloma.34 35
• FDA Adverse Event Reporting System (FAERS): Only one adverse event was reported, and it was from a 46-year-old male clinical trial participant. For the trial, the patient was receiving both TA-1 and an immunotherapy called peginterferon alfa-2a (PEG-INF). During the trial, the patient was hospitalized with anxiety, atrial fibrillation, and a “transient” decrease in his thyroid-stimulating hormone (TSH) levels. It’s noted that the use of both treatments makes it difficult to determine whether or not TA-1 played a role in these adverse effects, especially since they’re known potential side effects of PEG-INF.
• Patients undergoing deliberate immunosuppression: TA-1 may worsen or cause acute or chronic graft-versus-host disease (GVHD) and lead to engraftment failure in HSCT recipients.
• Immunogenicity concerns: In particularly high or concentrated doses above what’s typically used, TA-1 may pose a risk for immunogenicity. (This means large doses of TA-1 may provoke the immune system into producing too strong a response.)39
• As a vaccine adjuvant: Current safety information is insufficient.
• Foreign labeling safety details: Outside of the United States, approved TA-1 products include warnings against their use in children, pregnant and breastfeeding individuals, patients with autoimmune diseases, and immunosuppressed populations. Labeling in Indonesia also includes a warning of potential transient increases in liver enzymes.

Overall, the findings show that TA-1 appears to be generally safe for most adults when used in subcutaneous doses from 1mg to 16mg for up to a year.31 However, more research is needed, and this is one of many reasons to keep in close contact with your prescribing physician if you use TA-1 peptides.

Thymosin alpha-1 side effects

The insights we gained from knowledgeable experts regarding common TA-1 side effects were similar to the findings from most clinical studies, but there were also some additional symptoms reported by patients that are worth mentioning. The potential side effects of the peptide may include:

• Transient injection site swelling, redness, or discomfort
• Fatigue
• Headache
• Gastrointestinal discomfort

Additionally, if you ever experience any symptoms of an allergic reaction (e.g., hives, rashes, tongue swelling, throat closing, chest tightness, trouble breathing, anaphylaxis), then it’s important to stop using the peptide and either promptly contact your doctor or seek immediate medical attention if necessary.

Based on what we currently know about TA-1, the peptide may be most beneficial for adults (who aren’t pregnant or breastfeeding) with an immune-related concern or health condition. These may include, but aren’t limited to, people with: 7 36

• Chronic inflammation
• An autoimmune disease (especially research-supported applications like rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, or psoriatic arthritis)15 16
• Hepatitis B or C
• HIV/AIDS
• Certain cancers (as an adjunctive therapy with a doctor’s express permission)
• Mold toxicity
• Immune deficiency
• Long COVID
• ME/CFS
• Lyme disease
• Cystic fibrosis
• DiGeorge syndrome

In any case, it’s always vital to get your TA-1 through a qualified professional who has reviewed your medical history and cleared you to use the peptide.

Who should look elsewhere?

Thymosin alpha-1 isn’t an ideal option for everyone; in fact, the following populations may be better off looking elsewhere for support:

• Individuals with liver failure (TA-1 can temporarily increase ALT levels)
• Those undergoing intentional immunosuppression for MS, cancer, etc.
• People who are pregnant or breastfeeding
• Children or adolescents
• Those looking for benefits that TA-1 hasn’t demonstrated (like how another thymosin, TB4, may regenerate muscle tissue while TA-1 doesn’t appear to have that property)10
• Anyone who isn’t a fan of needles
• People who can’t afford to spend hundreds of dollars multiple times per year

As researchers learn about the peptide — including any additional potential applications or cases in which it’s not ideal — we’ll update this information accordingly.

Though TA-1 is often available as injections or a nasal spray, the former is far more common, so that’s the delivery method we’ll be detailing in this section.

Similar to the instructions for prescription thymalfasin (Zadaxin), TA-1 comes as a powder that you’ll have to reconstitute with the provided sterile water before it can be properly used.37 When it’s time to administer an injection, it should be given into subcutaneous fat (i.e., the stomach, thigh, arm).

Since TA-1 peptide therapy doesn’t appear to affect energy levels, it can be taken at any time of day (or night) — it all depends on your preference and routines.

Typically, TA-1 is administered as five injections weekly over the course of one month (four weeks of injections, five days each week). Following a month of treatment, patients take three months off. There are three “cycles” per year of the “one month on, three months off” protocol.

The potential side effects of TA-1 are generally mild and transient; they may include:

• Injection site reactions (e.g., redness, swelling, discomfort, etc.)
• Fatigue
• Headache
• Gastrointestinal discomfort

In order to reduce side effects, knowledgeable experts recommend trying some (or all) of the following:

• Start with a lower dose and gradually increase it as instructed by your doctor.
• Rotate injection sites with each dose to reduce irritation and discomfort.
• Keep hydrated to help manage symptoms like fatigue and headache.
• Take your peptide therapy with food if gastrointestinal symptoms occur.

Additionally, it’s important to maintain close communication with your doctor. They’ll be able to make sure your dosing is correct, and they may also be able to spot any adverse effects you may have missed (or wouldn’t know about).

Thymosin alpha-1 expected benefits timeline

The potential benefits of TA-1 peptide therapy can take time to become noticeable. Different effects may appear during the very short-, short-, and long-term use of the treatment.

• The first 1-2 weeks: Patients may notice better energy levels and a reduced number of infections as TA-1 enhances immune system function.
• After around a month: Improvements in immune cell activity and reductions in oxidative stress may be observed. Patients may have an enhanced response to vaccines and fewer symptoms of chronic infections.
• In the long term: Continued use of TA-1 may lead to sustained immune system improvements, greater resilience against infections, better management of chronic inflammatory conditions, and improvements in overall health. Additionally, patients with viral infections may have fewer relapses.

Currently, the only FDA-approved form of thymosin alpha-1 is Zadaxin (thymalfasin), a prescription drug used in the treatment of certain cancers and for chronic hepatitis B and C.13 Any other use of TA-1 is considered off-label and is not approved by the FDA.

There are doctors — often with specialty clinics — who prescribe TA-1 for off-label use. If you choose to go to one of them, it’s important to make sure that they use pharmaceutical-grade peptides, not research-grade ones. When peptides are research-grade, they’re meant to be used in research studies and are not held to the same strict purity and safety standards as pharmaceutical-grade ones.38 This is also one of the many reasons why we recommend against purchasing certain peptides from online distributors (except in cases like GLP-1s from reputable telehealth platforms).

As research develops and the market evolves, we’ll update this information accordingly with reliable — and safe — sources of thymosin alpha-1.