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Some human trialsNot FDA approved

Thymosin Alpha-1

Also known as: Ta1 · TA-1 · Thymalfasin · Zadaxin · Thymosin alpha 1

Updated 26 sources

A 28 amino acid thymus peptide that nudges T-cell immunity. Unlike most research peptides it has a label dose: as Zadaxin, approved outside the US for hepatitis B and C at 1.6 mg twice a week. Big trials are mixed: a 1,106-patient sepsis trial was null and the Cochrane hepatitis B review rates the evidence very low certainty. Not FDA approved; an FDA advisory committee voted 17 to 4 against compounding it.
Calculate with Thymosin Alpha-1Dosage chart

Quick facts

Half-life
  • About 2 hours after an injection under the skin, with peak levels at about 2 hours and no build-up between doses (label).
  • About 2 to 3 hours per guides; peak 1 to 2 hours after injection.
Routes
  • Subcutaneous injection
Forms
  • Vial (powder)
Reported dose ranges
  • 0.8 to 3.2 mg (subcutaneous injection)
  • 40 mcg/kg (subcutaneous injection)
  • 250 to 500 mcg (subcutaneous injection)
Vial sizes
  • 1.6 mg, 5 mg, 10 mg, 20 mg
Chemistry
  • 3,108.3 g/mol · C129H215N33O55 · CAS 62304-98-7
FDA status
  • Not FDA approved
WADA
  • Not confirmed

What people use Thymosin Alpha-1 for

  • General immune support, often framed as seasonal or when sick
  • Front-loaded courses at the start of an infection
  • Chronic hepatitis B and C (the label use outside the US)
  • Add-on during cancer treatment, as studied in melanoma and other cancers
  • Age-related immune decline, cycled 2 to 3 times a year
  • Stacks with LL-37, BPC-157, VIP or glutathione for immune defence, mold illness (CIRS) and anti-ageing

How it is thought to work. Thymosin alpha-1 acts on toll-like receptors 2 and 9 of dendritic and other antigen-presenting cells, which drives the adaptive T-cell response. It is cut from the larger protein prothymosin alpha and carries an acetyl group at its start. It is a different molecule from thymosin beta-4 (TB-500) despite the shared name.

Thymosin Alpha-1 dosing

19 protocols from studies, guides and community reports, grouped by goal. Tap a source badge to see where a number came from.

Standard immune support2

Standard immune support

Amount
1.6 mg
How often
Twice weekly, e.g. Monday and Thursday
Route
SubQ, vial (powder)
Cycle
8 to 12 weeks

Standard immune support (community)

Amount
1.5 mg
How often
Twice weekly
Route
SubQ, vial (powder)
Cycle
8 to 12 weeks

Daily low dose2

Daily low dose

Amount
300 to 500 mcg
How often
Once daily
Route
SubQ, vial (powder)
Cycle
8 weeks in the chart; 8 to 16 weeks commonly reported
Titration (2 steps) and details

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Daily low dose (community)

Amount
300 to 500 mcg
How often
Once daily
Route
SubQ, vial (powder)
Cycle
4 to 8 weeks

Other protocols: injected15

Chronic hepatitis B (label)

Amount
1.6 mg
How often
Twice a week
Route
SubQ, vial (powder)
Cycle
6 to 12 months
Timing and details

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Chronic hepatitis C with interferon (label)

Amount
1.6 mg
How often
Twice a week
Route
SubQ, vial (powder)
Cycle
12 months
Timing and details

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Under 40 kg (label)

Amount
40 mcg/kg
How often
Twice a week
Route
SubQ, vial (powder)
Timing and details

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Sepsis (TESTS trial)

Amount
1.6 mg
How often
Every 12 hours
Route
SubQ, vial (powder)
Cycle
7 days
Timing and details

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Hepatitis B trial

Amount
1.6 mg
How often
Twice a week
Route
SubQ, vial (powder)
Cycle
26 or 52 weeks
Timing and details

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Acute illness, front-loaded

Amount
1.6 mg
How often
Daily for 5 to 7 days, then twice weekly
Route
SubQ, vial (powder)
Cycle
1 week of daily loading, then 4 to 8 weeks twice weekly
Titration (2 steps) and details

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Longevity and prevention

Amount
1.6 mg
How often
Once or twice weekly
Route
SubQ, vial (powder)
Cycle
8 to 12 weeks, 2 to 3 cycles a year
Rest
4 weeks off between cycles

Label-based six-month course

Amount
1.6 mg
How often
Twice a week, 3 or 4 days apart
Route
SubQ, vial (powder)
Cycle
6 months, 52 injections

Conservative start, small frame

Amount
0.8 to 1.2 mg
How often
Twice weekly, 3 to 4 days apart
Route
SubQ, vial (powder)
Cycle
2 to 4 weeks, then step up to 1.6 mg

Short acute course

Amount
1.6 mg
How often
Once or twice daily
Route
SubQ, vial (powder)
Cycle
5 to 7 days only
Timing and details

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Intensive

Amount
3.2 mg
How often
Twice weekly
Route
SubQ, vial (powder)
Cycle
6 to 12 month courses for chronic conditions
Timing and details

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Low starting schedule

Amount
250 mcg
How often
3 times a week, then 500 mcg weekly to maintain
Route
SubQ, vial (powder)
Timing and details

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When sick (community)

Amount
1.6 mg
How often
Daily for 3 to 5 days, then twice weekly
Route
SubQ, vial (powder)
Cycle
2 to 4 weeks
Titration (2 steps) and details

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Long-term maintenance (community)

Amount
1.5 mg
How often
Once weekly
Route
SubQ, vial (powder)
Cycle
3 months on
Rest
1 month off
Timing and details

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Immune loading (community)

Amount
1 mg
How often
Daily
Route
SubQ, vial (powder)
Cycle
10 to 30 days

Doses shown are what sources report, labelled by origin. Not medical advice.

Full Thymosin Alpha-1 dosage guideEvery titration step in syringe units, missed doses and how to mix.

Vial strengths and syringe units

Every Thymosin Alpha-1 vial size with the water volumes sources use. Units are what to draw on a U-100 insulin syringe, worked out exactly.
Thymosin Alpha-1: concentration and U-100 syringe units for each vial size and water volume
WaterStrength300 mcgdose, units500 mcgdose, units1.6 mgdose, units
1.6 mg vial
1 mLRegulatory1.6 mg/mL18.80.188 mL31.30.313 mL1001 mL
5 mg vial
1 mLCompetitor guide5 mg/mL60.06 mL100.1 mL320.32 mL
2 mLCompetitor guide2.5 mg/mL120.12 mL200.2 mL640.64 mL
10 mg vial
1 mLCompetitor guide10 mg/mL30.03 mL50.05 mL160.16 mL
2 mLCompetitor guide5 mg/mL60.06 mL100.1 mL320.32 mL
3 mLCompetitor guide3.333 mg/mL90.09 mL150.15 mL480.48 mL
All 4 vial sizes on the dosage chart (1 more)
Units are on a U-100 insulin syringe (100 units = 1 mL). U-50 and U-30 barrels read the same units.Water volumes from

Doses shown are what sources report, labelled by origin. Not medical advice.

Calculate with this peptideYour vial, your water, your dose: Thymosin Alpha-1 in syringe units, with the math shown.

If you miss a dose

If a twice-weekly dose is 1 to 2 days late, take it and do not double up. Then reset so the next injection falls 3 to 4 days later, and add any skipped dose to the end of the course.

Thymosin Alpha-1 side effects

What trials and labels report, kept apart from what users and guides report. Frequencies are worded as each source states them.

Reported in studies and labels3

From clinical trials and regulatory documents.

  • Local discomfort at the injection site

    The main reported effect on the label; infrequent and mild

  • Redness, transient muscle wasting at the site, joint aches with hand swelling, rash

    Rare, per the label

  • Adverse events overall, sepsis trial

    66.4% on thymosin alpha-1 vs 67.6% on placebo; serious events 26.8% vs 29.3%

Reported by users and guides5

From community reports and dosing guides. Not measured rates.

  • Temporary liver enzyme (ALT) rise during hepatitis treatment

    Common in hepatitis B and C use; transient rise above 2 times baseline

    How people manage it

    • Liver tests every 3 months during hepatitis protocols

  • Fatigue, malaise or flu-like feeling

    Common in the first few days; flu-like symptoms usually pass within 48 hours

  • Low-grade fever, muscle aches, headache, temporary rash

    Less common

  • Hypersensitivity reaction

    Very rare

    How people manage it

    • Get emergency care for hives, lip or throat swelling, wheezing or faintness after an injection

  • Injection-site reactions and passing fatigue

    Occasional; some users link the fatigue to immune activation

All 8 Thymosin Alpha-1 side effects and how people manage themEvery management tip, who should not use it, and side-effect questions.

Who should avoid it

  • Deliberate immunosuppression, such as transplant recipientsCondition

    The label calls it contraindicated in people who are being deliberately immunosuppressed, since it pushes immune activity.

  • Known allergy to thymosin alpha-1Condition

    Contraindicated on the label.

  • PregnancyCondition

    Label Pregnancy Category C: only if the benefit clearly outweighs the risk. Guides advise against use in pregnancy and breastfeeding.

  • Active autoimmune flareCondition

    Extra immune stimulation could worsen an autoimmune flare; guides list it as a caution.

  • Biologics, systemic steroids or other immunosuppressantsSubstance

    Guides say only with a prescriber's sign-off, since the drugs pull in opposite directions.

  • Another drug in the same syringeSubstance

    Guides say never mix it with another drug in one syringe.

Storage

Powder (before mixing)

Temperature
2 to 8 °C

Zadaxin label: fridge at 2 to 8 C.

Powder (before mixing)

Temperature
-20 to 8 °C

Research powder: fridge at 2 to 8 C or freezer at -20 C, away from light. Short room-temperature trips are fine.

Mixed vial

Zadaxin mixed with its sterile water is single use: inject immediately.

Mixed vial

Temperature
2 to 8 °C
Use within
28 to 30 days

Research vials mixed with bacteriostatic water: fridge at 2 to 8 C, do not freeze, use within 28 to 30 days. Date the vial when you mix it.

Mixed with: Bacteriostatic water for research vials; sterile water for the 1.6 mg Zadaxin vial

Mixing. A 10 mg vial gives about 6 doses of 1.6 mg. Inject under the skin, never into a vein. Never mix it with another drug in the same syringe.

Stacks people report

Combinations from guides and community posts, with the reason given.
  • Epitalon

    Ta1 1.6 mg twice weekly for 8 to 12 weeks plus epitalon 5 mg a day for 10 to 20 days, pitched as an immune plus pineal longevity pair.

  • BPC-157

    Ta1 1.6 mg twice weekly plus BPC-157 250 to 500 mcg a day. BPC-157 also sits in a community mold illness (CIRS) stack with Ta1 and VIP.

  • TB-500

    Ta1 1.6 mg twice weekly plus TB-500 2 to 2.5 mg twice a week: immune support next to tissue repair.

  • LL-37

    The community immune defence stack: Ta1 for T cells, LL-37 for antimicrobial defence.

  • VIP

    Added for late-stage mold illness (CIRS) in a community stack with BPC-157.

  • Glutathione

    The community anti-ageing immune stack, pairing immune support with an antioxidant.

  • Thymalin

    A niche community pairing of the two thymus peptides during immune challenges.

  • GHK-Cu

    App users log Ta1 most often alongside GHK-Cu (6 of 7 reports), then MOTS-c, BPC-157 and KPV.

Compare Thymosin Alpha-1

Evidence and legal status

Evidence: some human trials

Many human trials, mixed results. Hepatitis B: Cochrane 2026 pooled 10 RCTs (1,349 people) and rated nearly all outcomes very low certainty. Sepsis: the TESTS trial (1,106 adults) found no 28-day mortality benefit. COVID-19: one retrospective study reported lower mortality, but a 9-study meta-analysis found none. General immune support, longevity and 'when sick' use in healthy people have no trial.

FDA and WADA

Not FDA approved

An approval withdrawn, or removed from FDA's compounding lists.

Not FDA approved. Listed by FDA among substances once in 503A Category 2 whose nominations were withdrawn, with concerns about immunogenicity and impurities. In December 2024 FDA's compounding advisory committee voted 17 to 4 against adding it to the 503A bulks list. Approved as Zadaxin in other countries, such as Singapore.

FDA staff proposed not listing either form; committee members cited no compelling evidence of effectiveness and safety. Ta1 is not among the peptides set for 2026 PCAC review. WADA 2026 does not name it (it names thymosin beta-4). S0 covers substances with no government approval for human use, and Ta1 is approved as Zadaxin in some countries, so S0 does not appear to apply. That is our reading; no WADA ruling was found.

WADA: Not confirmed

Thymosin Alpha-1 questions

What is thymosin alpha-1?

A 28 amino acid peptide from the thymus that acts on toll-like receptors 2 and 9 and pushes T-cell immunity. The synthetic drug is called thymalfasin, sold as Zadaxin outside the US.

What is the standard dose?

1.6 mg under the skin twice a week, 3 to 4 days apart. That is the Zadaxin label dose for hepatitis B (6 to 12 months) and hepatitis C (12 months), and nearly every guide anchors on it. People under 40 kg get 40 mcg/kg.

What dose do people use when sick?

Community and guide protocols front-load: 1.6 mg daily for 3 to 7 days, then twice weekly for a few weeks. No trial has tested this in otherwise healthy people. The closest test, 1.6 mg twice daily for 7 days in 1,106 sepsis patients, found no mortality benefit.

How many units is 1.6 mg?

With 10 mg in 2 mL (5 mg/mL), 1.6 mg is 0.32 mL, or 32 units on a U-100 syringe. With 10 mg in 1 mL it is 16 units. Use the calculator for your own mix.

Daily or twice a week?

The label and trials use twice a week, even though the half-life is only about 2 hours. One guide runs 300 to 500 mcg daily instead, and community users report a daily low-dose version, neither from a trial.

What do users report?

In one tracking app, 4 of 7 users logged 0.4 to 0.6 mg per injection and the rest 1 to 2 mg; all 7 rated it favorable, with recovery the most reported benefit. A community aggregate built on 80 reports describes it as very well tolerated.

Is thymosin alpha-1 FDA approved?

No. FDA lists it among substances once in 503A Category 2 whose nominations were withdrawn, citing immunogenicity and impurity concerns. In December 2024 FDA's compounding advisory committee voted 17 to 4 against adding it to the 503A bulks list.

Is it banned in sport?

WADA's 2026 list does not name thymosin alpha-1; it names thymosin beta-4 and TB-500. S0 bans substances with no government approval for human use, and Ta1 is approved as Zadaxin in some countries, so S0 does not appear to apply. That is our reading, not a WADA ruling.

Is it the same as TB-500?

No. Ta1 has 28 amino acids and works on immune signalling. TB-500 comes from thymosin beta-4 (43 amino acids) and is used for tissue repair. People often stack the two.

What is the half-life?

About 2 hours, with peak blood levels about 2 hours after the injection and no build-up between twice-weekly doses.

How long until it works?

Guides say immune blood markers shift within 2 to 4 weeks, with lymphocyte and CD4 changes over 4 to 8 weeks. In the hepatitis B trial the response kept rising after treatment ended and was clearest at 18 months.

Does it actually work?

It depends on the use. A 26-week course beat no treatment in one hepatitis B trial, but Cochrane rates the hepatitis B evidence very low certainty overall. The big sepsis trial was null, and a COVID-19 meta-analysis found no mortality effect.

What are the side effects?

Mostly mild discomfort at the injection site. The label lists rare redness, transient muscle wasting at the site, joint aches with hand swelling and rash. Guides add passing fatigue or a flu-like feeling in the first days.

Who should avoid it?

The label rules it out for people who are being deliberately immunosuppressed, such as transplant recipients, and anyone allergic to it. It is Pregnancy Category C. Guides add active autoimmune flares and use with biologics or steroids without a prescriber.

How do I store it?

Powder in the fridge at 2 to 8 C (the freezer also works for research vials). Mixed with bacteriostatic water, keep it at 2 to 8 C and use within 28 to 30 days. The Zadaxin vial mixed with sterile water is used immediately.

How long is a course?

The label runs 6 to 12 months. Guides use 8 to 12 week blocks with 4 weeks off, 2 to 3 times a year, or a 6-month course of 52 injections.

Ask about Thymosin Alpha-1

Answers come from this site's pages only, with a link to each source.

Sources

26 sources, each checked by date. Record updated Oct 24, 2026. Numbers are restated in our own words and labelled by where they came from.

Reference work1

  1. Thymosin alpha 1Wikipedia · checked Oct 24, 2026

Vendor guide2

  1. Thymosin alpha-1 catalog pageVendor product page · checked Oct 24, 2026
  2. Thymosin Alpha 1 (10 mg) product pageVendor product page · checked Oct 24, 2026

Competitor guide7

  1. Thymosin Alpha-1 (TA1) guidepeptidedosingprotocols.com · checked Oct 24, 2026
  2. Thymosin Alpha-1 dosage chartpeptidedeck.com · checked Oct 24, 2026
  3. Thymosin Alpha-1 (10 mg vial) dosage protocolpeptidedosages.com · checked Oct 24, 2026

Community-reported2

  1. Thymosin Alpha-1 community protocols and reportspeptideprotocolwiki.com, via a competitor guide · checked Oct 24, 2026
  2. Thymalin community protocols and reportspeptideprotocolwiki.com, via a competitor guide · checked Oct 24, 2026