Peptide guide

Thymosin Alpha-1

A 28-amino-acid immune-modulating peptide, sold internationally as Zadaxin (thymalfasin), studied for chronic hepatitis and immune support.

Thymosin Alpha-1 is a synthetic copy of a natural thymus peptide that tunes the immune system rather than pushing it in one direction. Unlike most research peptides, it has a deep human evidence base: it's approved as Zadaxin in more than 35 countries for chronic hepatitis B and C and as an immune adjuvant. It is not FDA-approved in the United States, where its compounding status has been in flux through 2026. People use it for immune resilience and recovery, so the practical questions are how to dose and store it correctly and how to tell a real source from a scam.

By the Zapify Research team

Reviewed against 10 clinical & research sources · Updated June 2026 · Educational use only

Type: 28-aa peptideImmune modulator
Route: Subcutaneous
Typical dose: 1.6 mg twice weekly
Cycle: Courses, not dailyweeks to months
Storage: Mixed: ~4 wksSealed: 2-8 °C
Status: Not FDA-approved

What is Thymosin Alpha-1?

A synthetic copy of a natural 28-amino-acid thymus peptide that modulates rather than stimulates the immune system; approved as Zadaxin abroad but not FDA-approved in the US.

Thymosin Alpha-1 is a peptide, a short chain of amino acids, that your body already makes. The thymus, a small gland behind the breastbone that schools your immune cells, produces it naturally. The version sold today, often written Talpha1 or thymalfasin, is a synthetic copy of that exact 28-amino-acid sequence. It isn't a foreign molecule engineered in a lab; it's a manufactured match for one your immune system has used your whole life.

What sets it apart from most peptides in this category is its job. It doesn't build tissue or push the immune system harder. It acts as a modulator, signaling through a receptor called TLR9 on immune cells to help T-cells mature and to rebalance an immune response that's either underreacting or running too hot. Think of it as recalibration rather than stimulation.

It also has something almost no research peptide can claim: a real clinical track record. Sold under the brand name Zadaxin, it's been approved in more than 35 countries for chronic hepatitis B, chronic hepatitis C, and as a vaccine adjuvant, and it's been given to hundreds of thousands of patients. The catch is geographic.

Thymosin Alpha-1 is not FDA-approved in the United States. It has never been brought to U.S. marketing approval, even though it's a registered medicine across much of Asia, South America, and parts of Europe. Its U.S. compounding status has also shifted through 2026: the FDA kept it off the approved bulk-substance list for compounding (Category 2) early in the year, and a later HHS announcement signaled a reversal. For an American buyer, none of that adds up to an approved, prescribable drug.

What is it studied for?

The human data is real, not a rat-study backfill: over 11,000 people across 30-plus trials, with post-marketing coverage reported above 600,000 patients.

The evidence here is unusual for a peptide. More than 11,000 people have been enrolled across 30-plus clinical trials, and post-marketing surveillance is reported to cover over 600,000 treated patients in countries where it's approved. That doesn't make every use proven, but it does mean the human data is real, not a backfill of rat studies the way it is for most compounds in this space.

Evidence base, by subject

30+ trials, 11,000+ subjectsHuman clinical experience

robust for hepatitis B; mixed for sepsis/COVIDStrength varies by indication

The research clusters in a few areas, and the quality of evidence is very different across them:

Chronic viral hepatitisThe strongest data. Randomized trials support 1.6 mg twice weekly for chronic hepatitis B, and it's an approved indication in many countries, often alongside antivirals or interferon.

Immune support & vaccine responseUsed as a vaccine adjuvant and studied in patients with weakened immunity. The idea is restoring T-cell balance rather than blanket stimulation.

Critical illness: sepsis & COVID-19Heavily studied but genuinely mixed. Some earlier trials and a meta-analysis hinted at a mortality benefit; a large Phase III sepsis trial then found none overall. Treat this as unsettled.

The mechanism is better understood than for most peptides, though not fully mapped. The evidence indicates Talpha1 signals through Toll-like receptors, prominently TLR9, on dendritic cells and influences the maturation and balance of T-cells, helping restore a more normal Th1/Th2 ratio. How much that translates into benefit outside the approved hepatitis indications, especially for the general immune support people buy it for, is where the evidence thins out.

Why people use it

People use it for immune resilience and recovery, but for healthy people seeking general support the direct human evidence is thin despite strong hepatitis B trial data.

Most people who try Thymosin Alpha-1 land in one of a few situations. These are the reasons they reach for it, not proof it delivers for each one:

A run of frequent infections or the sense of a sluggish, worn-down immune system, often after illness or a stretch of high stress.
Wanting immune support during cold and flu season or around travel, drawing on the vaccine-adjuvant research.
A chronic viral or inflammatory condition where their own clinician has raised it, which is closest to its approved use abroad.
Recovery from a long illness or hard training block, where the appeal is rebalancing rather than stimulating the immune response.

For most of these everyday uses, there's no U.S.-approved indication and the direct human evidence is thin, especially for healthy people seeking general immune support. What's genuinely strong is the rest of the picture: decades of clinical use abroad, a clean safety record across thousands of patients, a plausible and partly mapped mechanism, and solid trial data in chronic hepatitis B. That makes it one of the more credible peptides to be curious about. It still isn't a substitute for the basics that move immune health most, including sleep, vaccination, and managing the conditions a doctor can actually treat.

How to reconstitute Thymosin Alpha-1

A 10 mg vial in 2 mL gives 5 mg/mL, so a 1.6 mg dose is 0.32 mL, or 32 units on a U-100 syringe.

Your vial arrives as a small puck of dry powder. Before you can use it, you mix it into a liquid. That step is called reconstitution, and it's the same process used for most research peptides. It looks more intimidating than it is.

Step 1Start with powderWipe the rubber stopper with an alcohol swab.

Step 2Add bac. waterRun it slowly down the inside wall — never shake.

Step 3Draw your doseThe calculator gives the exact units to draw to.

Wipe the rubber stopper with an alcohol swab first, every time.
Use bacteriostatic water, not plain sterile water and not saline. The trace of benzyl alcohol in it holds back bacteria, which matters because you'll be drawing from the same vial for weeks.
Add the water slowly, running it down the inside glass wall. Don't blast it straight onto the powder.
Don't shake it. Swirl gently and let it dissolve on its own. Shaking foams the solution and can damage the peptide.

A common setup is a 10 mg vial mixed with 2 mL of bacteriostatic water, which gives 5 mg/mL. At that concentration a 1.6 mg dose is 0.32 mL, or 32 units on a U-100 insulin syringe. The water doesn't change how much peptide is in the vial; it only sets the concentration, which decides how many units you draw. More water means a more dilute mix and a bigger draw for the same dose. You can't ruin it with too much or too little, you only change the draw math, and that's exactly what the calculator handles.

Calculate your exact Thymosin Alpha-1 reconstitution →

Dose & units

No US-approved dose exists; the consistently reported figure, studied in hepatitis B trials, is 1.6 mg subcutaneously twice a week, 3–4 days apart.

There is no FDA-approved dose for Thymosin Alpha-1 in the United States. The numbers below come from the approved Zadaxin labeling abroad and from clinic write-ups, which is more grounding than most peptides have, but it still isn't a U.S. medical standard. Decide what goes into your body with a licensed provider, not with this page.

Typical range

The most consistently reported dose, and the one studied in chronic hepatitis B trials, is 1.6 mg given subcutaneously twice a week, with the two shots spaced 3 to 4 days apart. Labeling also describes a body-surface-area equivalent (around 900 mcg/m2), and for smaller adults the dose is scaled down accordingly.

Titration

There isn't much to titrate; the 1.6 mg figure is a fixed clinical dose rather than something people ramp up. If anything, a cautious start means beginning at the standard dose and watching for the mild injection-site reactions that are the most common effect before settling into a routine.

Cycling

This is run as a course, not a forever protocol. In its approved hepatitis use, a typical course runs about 6 months, extending toward 12 in some combination regimens. For the shorter immune-support courses people use off-label, write-ups vary widely and the numbers are far softer, which is part of why a provider belongs in the loop.

Onweeks to ~6 months

Off / reassesswith a provider

For the exact mark to draw to on your insulin syringe, don't eyeball it. The calculator turns your vial size, water, and dose into the precise number of units.

Get your exact units →

Storage

Sealed lyophilized powder is kept refrigerated at 2–8 °C long-term; once mixed, refrigerate and use within about 4 weeks before contamination limits it.

Sealed & drySealed lyophilized powder stays stable for months, kept refrigerated at 2–8 °C long-term though it tolerates shipping at room temperature.

ReconstitutedRefrigerate in the main compartment and use within about 4 weeks; don't freeze, keep out of light, toss if cloudy or discolored.

You'll see longer windows quoted for peptide vials. Those figures are beyond-use dates for a sealed, unmixed vial that a compounding pharmacy has stability-tested, and they stop applying the moment you add water. A mixed vial runs on the roughly four-week clock instead, because that's how long the preservative in bacteriostatic water reliably keeps the solution clean once you're drawing from it.

That four-week limit is about contamination, not potency; the peptide itself often stays good well beyond it. Reconstitute with plain sterile water instead of bacteriostatic and you drop to a day or two, since there's no preservative holding bacteria back.

Don't freeze a reconstituted vial, keep it out of direct light, write the mix date on the label, and throw it out if the solution ever turns cloudy or discolored, whatever the date says.

Side effects & safety

One of the cleaner safety records here, backed by human data; as an immune modulator it isn't WADA-listed, but autoimmune or transplant patients should check with a doctor.

Thymosin Alpha-1 has one of the cleaner safety records in this whole category, and unlike most peptides that claim is backed by human data rather than rat studies. Safety reviews drawing on thousands of treated patients describe adverse events as infrequent and mild.

Most common: mild, short-lived redness, irritation, or discomfort at the injection site.
Less often: transient mild fatigue, and rarely rash, joint aches, or brief swelling that resolve on their own.

Because it modulates the immune system, talk to a doctor first if you have an autoimmune condition, are on immunosuppressant medication, or have had an organ transplant, where nudging immune activity could cut the wrong way. The same goes if you're pregnant or breastfeeding. The reassuring safety record comes from supervised medical use abroad, not from unsupervised self-dosing.

For athletes, this one is different from the recovery peptides. Thymosin Alpha-1 is an immune modulator, not a growth factor, so it isn't named on the WADA Prohibited List the way thymosin beta-4 and TB-500 are. That said, anti-doping rules and example lists change, so anyone who competes should confirm current status through GlobalDRO rather than assuming.

And the biggest risk here isn't really the molecule, which has decades of supervised use behind it. It's whether what's in the vial is actually Thymosin Alpha-1, at the strength on the label. That comes down to where you buy it.

How to vet a source

A 28-amino-acid peptide is long enough that a wrong sequence shorts you invisibly in powder — demand a batch-specific third-party COA matching your vial's lot number.

This is an unregulated gray market, and a real share of independently tested vials come back underdosed, impure, or not even the compound on the label. A 28-amino-acid peptide is long enough that an incomplete or wrong sequence is an easy way to get shorted, and you can't see it in the powder. Where you buy matters more than almost anything else here. The one document that separates a real seller from a gamble is a certificate of analysis: a third-party lab's report on what's actually in the vial.

A real COA shows

An identity test (usually mass spectrometry) confirming the peptide is what the label says.
A purity figure from HPLC, typically 98% or higher.
A lot or batch number that matches the number printed on your vial.
A named, independent accredited lab and a recent test date.

Walk away if

There’s no COA, or it’s a generic image with no lot number.
The “certificate” comes from the seller instead of a third-party lab.
The lot number doesn’t match your vial, or there isn’t one at all.
It’s a flat image you can’t trace back to the lab that issued it.

That's the standard worth holding any seller to, ours included. Ask for the batch-specific COA before you buy, match the lot number to your vial, and don't accept a screenshot in place of a traceable report.

See the Zapify compound catalog →

Common questions about Thymosin Alpha-1

Is Thymosin Alpha-1 FDA-approved?

No. It is not FDA-approved for any use in the United States, and it has never been brought to U.S. marketing approval. It is, however, an approved prescription medicine (brand name Zadaxin, generic thymalfasin) in more than 35 countries for chronic hepatitis B, chronic hepatitis C, and as an immune adjuvant. Its U.S. compounding status shifted in 2026: the FDA kept it off the approved bulk-substance list for compounding (Category 2) early in the year, and a later HHS announcement signaled moving it back. For a U.S. buyer, none of that makes it an approved drug.

Why is it approved abroad but not in the U.S.?

It isn't a question of the science being weaker. The manufacturer reportedly judged the cost and timeline of U.S. registration trials to be hard to justify given the market it already serves elsewhere, so a marketing application was never completed. That leaves a compound with a large international evidence base and no U.S. approval at the same time, which is unusual.

How is it different from TB-500 or BPC-157?

Different purpose entirely. BPC-157 and TB-500 are recovery peptides aimed at tendon, muscle, and soft-tissue repair, and their evidence is almost entirely from animals. Thymosin Alpha-1 is an immune modulator with a deep human clinical record and actual approvals abroad. One practical consequence for athletes: TB-500 (a thymosin beta-4 fragment) is banned by WADA, while Thymosin Alpha-1, being an immune modulator rather than a growth factor, isn't named on the prohibited list.

Does it have real human evidence, or just animal studies?

Real human evidence, which is rare in this category. More than 11,000 subjects across 30-plus clinical trials, plus post-marketing data reported on over 600,000 treated patients. The strength varies by use: the chronic hepatitis B data is solid, while results in sepsis and COVID-19 are genuinely mixed, with a large Phase III sepsis trial finding no overall mortality benefit. General immune support in healthy people is the least-studied use.

Why bacteriostatic water and not saline or sterile water?

Because you'll be drawing from the same vial across weeks. Bacteriostatic water carries a trace of benzyl alcohol that holds back bacteria between draws; plain sterile water and saline have no preservative. On a multi-dose peptide vial, the professional sources all point the same way: bacteriostatic.

References

This page is for research and educational purposes only. It is not medical advice or a recommendation to use any compound. The dose ranges shown are reported by clinics and research literature, not validated medical standards, and Thymosin Alpha-1 is not FDA-approved. Talk to a licensed medical provider about anything you put in your body.