Thymosin Alpha-1_Dosage, benefits & legal status
Also known as thymalfasin, Zadaxin, Ta1
A well-studied shot that tunes up the immune system.
Common vial size is what vendors typically sell, not a recommendation. Enter your own vial in the calculator.
What is Thymosin Alpha-1?
Plain language first. The technical label stays, but it never stands alone.Overview
It tunes up the immune system to respond better to infection. It is well studied, and used abroad as an add-on therapy.
Thymosin Alpha-1 is a 28-amino-acid peptide made by the thymus that helps direct immune defenses.
What it's used for
A shot that tunes up your immune system, used for chronic infections, immune resilience, and as an add-on therapy abroad. It is well studied.
How does Thymosin Alpha-1 work?
What it does in the body, and where.Thymosin alpha-1 is made by your thymus, the gland that trains your immune cells. It is one of the better-studied peptides here and is an approved drug in more than thirty countries.
- 01It matures and directs T cellsT cells are the part of your immune system that recognises specific threats, and this peptide helps them develop and respond.
- 02The response is tuned, not amplifiedIt appears to improve how well the immune system responds rather than simply increasing activity, which matters because more immune activity is not always better.
- 03Approved abroad, not in the USUsed for hepatitis B and C and as an adjunct in some cancers in other countries. It has not been FDA-approved.
Where this compound is thought to act.
What else is it used for?
Each use below carries its own evidence level. Approved means regulators have cleared it for that purpose. Investigational means it is in trials. Early research means it is being studied and is not established.
- Helping the immune system fight chronic hepatitis B, approved in more than 35 countries as Zadaxin but not in the United StatesClinical use
- Supporting the immune system alongside cancer treatment in some countriesClinical use
- Severe infection and sepsis, where a large 2025 trial did not show a clear benefitInvestigational
The published record
872
Records indexed for Thymosin Alpha-1400 papers and 64 trials indexed in detail.
231 in humans, 122 of them original studies.
64 registered trials, 2 with posted results.
FDA: Category 3 · FDA: Nominated but withdrawn; previously category 2.
Counted from Europe PMC indexing, not read by a person. Human means indexed under humans, which includes reviews and work on human cells. Original studies exclude reviews and lab work on human cells.Last updated 12 September 2026.
At a glance
Four things to know about Thymosin Alpha-1
Evidence
Clinical use
Category
Immune support
Common vial
5 mg
Half-life
About 2 hours
How much, and do you cycle it?
The range, and whether you take breaks.1.6 mg per dose, 2x per week. Given as a defined course, typically twice weekly over monthsClinical use
Where it is registered, it is prescribed as a course rather than continuously: commonly twice-weekly injections over a set number of months for hepatitis B, or a short course alongside a vaccine. The course length comes from the indication, not from tolerance.
How long does it stay in the body?
The half-life, and where the figure comes from.About 2 hoursHuman study
Approved in more than 35 countries as Zadaxin but not in the US, so there is no FDA label to read. The immune effects reported in trials outlast the two hours substantially, which is why dosing is twice weekly.
Source: https://pubmed.ncbi.nlm.nih.gov/11381492/
You can compare this against the whole library to see where it sits.
How do I dose and price it?
Enter your vial and your dose. Pick a mix. We show the draw and the cost.The vial holds a fixed amount of drug. Adding more water does not make more drug, it just spreads it thinner, so you draw a bigger number on the syringe for the same dose.
Choose your mix
Measuring the water1 mL = one full 100-unit syringe.
Your draw
64 / 100 unitsThymosin Alpha-1 starts at $26.00 across 39 vendors, typically $4.90 – $13.00 per mg.
59 listings, last read Sep 5, 2026. Shipping and card fees are not included.
How do you store it?
Before mixing, and after.Dry powder in the freezer or fridge. Once mixed, fridge, and use within about a month.
Unmixed lyophilized Thymosin Alpha-1 keeps for a long time cold. Once you add water the clock starts: most reconstituted vials hold up for roughly 28 to 30 days at fridge temperature. Keep it out of light, and do not freeze it after mixing.
What are the side effects and cautions?
Known cautions and warnings for this compound.Who should avoid it
- Immunosuppressive therapy, including after an organ transplant
- Pregnancy
Stop and get help
- Signs of an allergic reaction
- Worsening of an autoimmune condition
Common effects
- Injection-site redness, which is the most common effect
- Generally very well tolerated
- Occasional short-lived fatigue
What regulators say
- FDA: Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (category 2 and withdrawn nominations), current as of April 22, 2026Nominated but withdrawn; previously category 2Checked 11 September 2026
- FDA: Bulk Drug Substances Nominated for Use in Compounding Under Section 503B (interim categories 1, 2, 3), updated March 21, 2025Category 3
Nominated without adequate support
Checked 11 September 2026
Where this page says nothing is established, that means nobody has studied it, not that a compound is safe.
Is Thymosin Alpha-1 approved?
And where the numbers on this page come from.Not approved, but legal to obtain. Thymosin Alpha-1 has no FDA approval, and it can be prescribed or prepared by a compounding pharmacy in the United States. It is approved in 35+ countries, but not in the United States.
- Approval statusClinical use
- RouteUnder the skin (subcutaneous)
- CheckedSeptember 2026
- Approved outside the US35+ countries: Approved in more than 35 countries as Zadaxin. Holds only orphan-drug designation in the US.This does not change the United States position above.
What has happened recently
Not FDA-approved in the United States, where it holds only orphan-drug designation. It is approved and used in more than 35 other countries.
You can compare this against the whole library, or read how to check a seller.
- DoseFrom product labeling and clinical guidelines.
- Vial sizeFrom what vendors typically list; not a recommendation.
- Sources
- Reviewed8 September 2026
What else is like Thymosin Alpha-1?
Others in Immune support, side by side.If you're weighing Thymosin Alpha-1, it's worth reading LL-37, Thymulin, and Thymogen in the same class.
A well-studied shot that tunes up the immune system.
- Dose
- 1.6 mg per dose
- How often
- 2x per week
A natural germ-fighting peptide for stubborn infections and wound healing.
- Dose
- 0.1 up to 0.5 mg per dose (start low, increase slowly)
- How often
- Daily, short courses
A thymus peptide studied for immune balance and calming inflammation.
- Dose
- 1 mg per dose
- How often
- Daily/weekly
A short immune bioregulator taken in courses, with thin evidence.
- Dose
- Varies (course-based)
- How often
- Courses
Guides for this compound
- How to Reconstitute a Peptide
Mix peptide powder with bacteriostatic water, step by step.
- How to Read an Insulin Syringe
Read the units, convert to millilitres, and draw the exact dose.
- mcg vs mg: The Peptide Dosing Mistake to Avoid
Your vial says mg and your protocol says mcg. Here is the conversion and how to check it.
Sources
- Thymosin alpha-1, pharmacology review, Am J Health Syst Pharm(2001)Peak serum concentration within two hours, serum half-life approximately 2 hours, blood levels back to baseline within 24 hours. A review, not an original trial.
- FDA, bulk drug substances for compounding that may present significant safety risks(2026)FDA cites immunogenicity risk for certain routes and complexities with peptide-related impurities and characterisation, and describes the safety-related information as inadequate for the agency to understand the extent of any safety issues the proposed compounded drug raises. Note that this is a compounding judgement about a US bulk substance, and is separate from thymalfasin's approval status elsewhere. As of the 22 April 2026 version of this page, the substance sits in the second table, headed bulk drug substances nominated but withdrawn, rather than in the live category 2 list. The nomination was withdrawn, which is not the same as being approved or cleared: FDA still publishes the safety language above, and no longer has a nomination in front of it to evaluate.
Last reviewed 8 September 2026
Beyond these, 464 records are indexed. Browse the records