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Immune system

Thymosin Alpha-1

An immune-modulating peptide. Tends to bring an out-of-balance immune system back into balance.

3 min read 8 sources

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Thymosin Alpha-1 vial with the black TPD label on a white podium, next to a large molecule model of blue and white spheres in a bright lab
Compound approved · in over 35 countries, not in the US

Summary

At a glance

Sources checked on 26 Oct 2026

Length
28 amino acids

made synthetically, as a drug it is called thymalfasin8

Approval
>35 countries

for hepatitis B and C and as an immune enhancer, according to a 2009 review5

Largest sepsis trial
1,106 participants

TESTS, double-blind versus placebo, no clear difference in mortality2

Half-life
~1.5 hours

as cited in the TESTS trial, a dose stays in the blood only briefly2

  • Thymosin Alpha-1 is a peptide of 28 amino acids that originally comes from the thymus. Made synthetically it is called thymalfasin.8
  • According to a review thymalfasin is approved in over 35 countries, mainly for hepatitis B and C and to strengthen the immune system. It is not approved in the US.58
  • In cell and mouse experiments it activated dendritic cells via the receptor TLR9 while also promoting regulatory T cells. So it tends to balance rather than only stimulate.6
  • In the first sepsis trial 26 versus 35 percent died, a difference that just missed certainty. The larger double-blind TESTS trial with 1,106 people found no difference.12
  • Side effects occurred as often in TESTS as on placebo. Everything here is the state of research, not a recommendation.2
Profile

Updated May 2026

Class
Immune-modulating peptide

thymus-derived

Route
Subcutaneous
Frequency
~2x per week

in phases

Form
Lyophilised powder

reconstituted with BAC water

Sizes
5 to 10 mg

2 sizes in the shop

Contents 16 sections
  1. At a glance
  2. What is Thymosin Alpha-1?
  3. How it works
  4. What you need
  5. Reconstitution
  6. Injection
  7. Dosing
  8. What the research shows
  9. Research status
  10. Side effects
  11. Practice
  12. Storage
  13. Related compounds
  14. FAQ
  15. Glossary
  16. Sources

What is Thymosin Alpha-1?

Thymosin Alpha-1 is a body-near peptide that originally comes from the thymus, the organ in which part of the immune cells mature. In a research context it is used as an immune modulator: it is meant to bring an out-of-sync immune system into balance rather than crudely ramping it up.

It is used subcutaneously, dosed in milligrams. It ships as a freeze-dried powder you dissolve in bacteriostatic water.

Comparison

Peptides around the thymus

Peptides from the TPD lexicon that relate to the thymus. Tap a card to open its entry.

28 amino acids, approved Thymosin Alpha-1 TLR9
9 amino acids, needs zinc Thymulin NF-κB Peptide mixture from the thymus Thymalin Dipeptide Glu-Trp Thymogen Thymosin beta-4, a different protein TB-500 (Thymosin Beta-4)

A similar origin does not mean the same effect. Thymosin beta-4 has a similar name but is a different protein. 65

How it works

Thymosin Alpha-1 acts on the maturation and activation of T cells and other parts of the immune defence. The effect is regulating rather than one-sided: a weak defence can be supported, an overshooting reaction dampened. That is exactly why it has been studied clinically in contexts as different as infections and vaccine support.

So it is not a "booster" in the crude sense, but an agent that pushes the immune system toward balance.

Where it acts

Where Thymosin Alpha-1 was studied

Tap a point or a card. Colour = receptor from cell studies, grey = finding from trials.

  1. Immune cells

    Activates dendritic cells via TLR9 and promotes regulatory T cells (cell and mouse studies)6

    TLR9
  2. Liver

    Approved for hepatitis B and C in over 35 countries5

    Observed in trials
  3. Pancreas

    Severe inflammation: infections not certainly rarer than on placebo3

    Observed in trials
  4. Skin (melanoma)

    Added to chemo longer median survival, not statistically certain4

    Observed in trials

Known targets6

Compound CHEMBL2103979: one described target, Signal in dendritic cells (cell and mouse studies), ChEMBL lists no confirmed mechanism.

Toll-like receptor 9
Gene
TLR9
UniProt
Q9NR96
ChEMBL
CHEMBL5804
Action
Signal in dendritic cells (cell and mouse studies), ChEMBL lists no confirmed mechanism
Glowing blue immune cells with short projections, surrounded by blue 3D peptide chains
Thymosin Alpha-1 acts via immune cells. Symbolic image.

What you need

For subcutaneous use you need:

Supplies

5 things, numbered as in the picture

Tick off what you already have. Vial and BAC water are our real shop photos at the same size.

Thymosin Alpha-1 vial and bacteriostatic water at the same size with the black TPD label, next to two U-100 insulin syringes, two alcohol swabs and a sharps container with a blue lid

  1. Thymosin Alpha-1 vial

    The Thymosin Alpha-1 vial with the freeze-dried powder

    In the shop

  2. Bacteriostatic water

    Bacteriostatic water to dissolve it

    In the shop

  3. U-100 insulin syringes

    U-100 insulin syringes

    Amazon (opens a new tab)

  4. Alcohol swabs

    Alcohol swabs for the vial cap and the skin

    Amazon (opens a new tab)

  5. Sharps container

    A sealable sharps container for used needles

As an Amazon associate we earn from qualifying purchases. Links open Amazon - no extra cost for you.

Reconstitution

The powder is dissolved in bacteriostatic water. How much water you add sets the concentration and therefore how many units you draw for your dose on the insulin syringe.

Use the peptide calculator for this: pick your vial size and the water volume to see the concentration and units per dose.

When dissolving, just add the bac water, it does not matter if it hits the powder directly. Then swirl or shake until everything has dissolved, both are fine.

Step by step

Dissolving the powder

Four steps, the same for every vial size.

  1. 1Wipe the cap

    Clean the rubber stopper with an alcohol swab.

  2. 2Add BAC water

    Just add it, it does not matter if it hits the powder directly.

  3. 3Swirl or shake

    Until everything has dissolved, both are fine.

  4. 4Draw up

    With the U-100 insulin syringe.

Less water higher concentration fewer units on the syringe Example: 5 mg + 2 ml = 2.5 mg/ml

Injection

The injection is subcutaneous, into the fat layer under the skin, classically the abdomen (keep clear of the area around the navel), the front and the inner side of the thigh or the back of the upper arm.

Injection

Where and at what angle

Pick a spot or switch the angle. Subcutaneous means: into the fat layer, not the muscle.

Rotate the spot each time, never the same one twice in a row.

90°More fat under the skin

Rule of thumb: where there is more fat under the skin, insert straight at 90 degrees. In lean people with little fat, 45 degrees, so the needle stays in the fat layer. Simplified diagram.

  1. Clean the spot with an alcohol swab and let it dry

  2. Pinch up a small fold of skin

  3. Insert the needle: at 90 degrees where there is more fat under the skin, at 45 degrees in lean people with little fat

  4. Inject slowly, wait a moment, then withdraw

  5. Put the needle straight into the sharps container

Rotate the site.

Dosing

Dosing

Dosing, titration and syringe

Loading the dosing information …

  • Getting started and stepping up, drawn as a staircase
  • Units on the U-100 syringe for every step
  • How long one vial lasts

What the research shows

Thymosin Alpha-1 is surprisingly well studied clinically. A multicentre randomised trial (ETASS, 2013) tested it in patients with severe sepsis and found signs of improved immune function. Alongside, there are clinical data from other areas such as infections and vaccine support. For a peptide, the data base is therefore comparatively solid.

The study with a link is in the source block below.

Study results

What the trials measured

Interactive: switch tabs, tap points, show or hide arms. Arms are named relative to each other, no dosing advice.

Died within 28 days12

Share in percent, two trials from China with 361 and 1,089 people analysed

ETASS (2013)1 single-blind
Thymosin Alpha-1 26.0%
Standard care without placebo 35.0%
TESTS (2025)2 double-blind
Thymosin Alpha-1 23.4%
Placebo 24.1%

In ETASS the difference just missed certainty and the comparison group received no placebo. The larger TESTS trial with placebo found no difference. A subgroup aged 60 and over showed a possible benefit there, which counts only as a hint.

Complications in severe pancreatitis3

Share in percent, 508 people, TRACE trial versus placebo

Infected dead tissue3
Thymosin Alpha-1 15.7%
Placebo 18.1%
New organ failure3
Thymosin Alpha-1 10.6%
Placebo 15.0%

The main goal, fewer infections, was not reached. The trial found no certain difference in the other complications either.

Survival in advanced melanoma4

Median in months, 488 people, Thymosin Alpha-1 added to chemo

Median survival4
Thymosin Alpha-1 9.4%
Chemo plus interferon (control) 6.6%

The difference was not statistically certain. More tumours responded in two groups with Thymosin Alpha-1 and there were no extra side effects.

Petri dishes with blue cultures, a glass thymus with two lobes in the middle, next to a pipette and citrus slices
The data come from cell studies and clinical trials. Symbolic image.

Research status

Where the research stands

A selection of registered trials with thymalfasin, often added to standard care. Most trials run in China. As of 26 Oct 2026. 7

  1. Preclinical Cell and mouse studies: dendritic cells and TLR9
  2. Phase 1 2 trials, 1 completed
  3. Phase 2 3 trials, 3 completed
  4. Phase 3 4 trials, 2 completed
  5. Approval in over 35 countries, not in the US
3,742 participants in phase 3 Planned figures for running trials According to a review thymalfasin is approved in over 35 countries, mainly for hepatitis B and C and as an immune enhancer, as a powder to dissolve and inject under the skin. ChEMBL lists it at phase 3, there is no approval in the US.5
Show all 11 trials on a timelineHide timeline 9 completed 2 running 4 with results
Phase 2
Phase 3
Phase 4
Without phase

Bar: start to primary endpoint (planned for running trials). Green = completed, blue = progress until 26 Oct 2026. Phase 1: 2 trials on safety and pharmacokinetics, not shown as bars.

Side effects

Thymosin Alpha-1 is considered very well tolerated; in the studies side effects were rare and mostly mild, most likely injection-site reactions. Because it is immune-modulating, restraint makes sense with existing autoimmune issues, where medical advice is worthwhile when in doubt.

Tolerability

Side effects in the sepsis trial TESTS

Out of 100 participants per group in TESTS, how many had the event. All participants were in intensive care with sepsis.

66 of 100 Thymosin Alpha-1
68 of 100 Placebo
Event Thymosin Alpha-1Placebo
Adverse events2 66%68%
Serious events2 27%29%

Most events stem from the serious underlying illness, which is why they are common in both groups. Thymosin Alpha-1 made no difference.2

Practice

  1. Use in phases, e.g

    for support over a few weeks.

  2. Sleep, nutrition and stress management are the base of any immune strategy.

  3. With an autoimmune history, be cautious and check with a doctor when in doubt.

Bowl of lemons and oranges, a cup of tea and a light blue sleep mask on a white table

Storage

The undissolved powder is robust, normal room temperature (around 20 to 25 degrees) is fine, ideally kept in the dark. The reconstituted solution goes into the fridge (2 to 8 degrees) and stays stable there for at least 4 to 6 months with barely any loss of potency, in practice considerably longer. The bacteriostatic water brings a preservative that keeps the dissolved form stable for longer.

Shelf life

How long it keeps

Undissolved (powder) Room temperature, around 20 to 25 degrees, dark

Robust, no fridge needed. Keeps for several months without trouble.

Dissolved (mixed) Fridge, 2 to 8 degrees

At least 4 to 6 months with barely any loss of potency. The bacteriostatic water brings a preservative.

  • Keep it dark
  • Dissolved: 2 to 8 degrees
  • Note the mixing date on the vial
Nine vials with white powder and blue caps in the door shelf of a bright fridge
Powder dark at room temperature, once dissolved into the fridge (2 to 8 degrees), stable there for at least 4 to 6 months. Symbolic image.

Related

Related compounds

A different path: all in the TPD lexicon.

Thymosin Alpha-1
Thymulin Another thymic hormone, works only with zinc Thymalin Peptide mixture from the thymus Thymogen Thymic dipeptide from the Khavinson programme TB-500 (Thymosin Beta-4) Similar name, a different protein with a different effect LL-37 The body's own defence peptide KPV Anti-inflammatory tripeptide, preclinical VIP Neuropeptide, also studied as an immune regulator

FAQ

Common questions about Thymosin Alpha-1

Short answers, each backed by the sources below.

Is Thymosin Alpha-1 approved?

Yes, but not everywhere. As thymalfasin it is approved in over 35 countries according to a 2009 review, mainly for hepatitis B and C and to strengthen the immune system. There is no approval in the US, ChEMBL lists the compound at phase 3.58

How does Thymosin Alpha-1 work?

In cell and mouse experiments it made dendritic cells more active, the cells that show pathogens to the immune system. This ran via the receptor TLR9. At the same time it promoted regulatory T cells, which slow down excessive reactions. ChEMBL lists no confirmed mechanism in humans.68

What do the sepsis trials show?

In ETASS with 361 people 26 percent died within 28 days with Thymosin Alpha-1 and 35 percent without, a difference that just missed certainty. The larger TESTS trial with 1,106 people and placebo found 23.4 versus 24.1 percent, so no difference. A possible benefit from age 60 counts only as a hint there.12

Are there data on cancer?

In a trial with 488 people with advanced melanoma Thymosin Alpha-1 was added to chemo. The highest study dose was 6.4 mg. More tumours responded and median survival was 9.4 versus 6.6 months, but not statistically certain. There were no extra side effects.4

Does it help in severe pancreatitis?

Not with certainty in the TRACE trial with 508 people. Infected dead tissue occurred in 15.7 percent with Thymosin Alpha-1 and 18.1 percent on placebo. The main goal was therefore not reached.3

Which side effects are known?

In TESTS 66.4 percent on Thymosin Alpha-1 and 67.6 percent on placebo had an adverse event, serious events were 26.8 versus 29.3 percent. ETASS recorded no serious side effects caused by the drug. With autoimmune disease the regular entry advises restraint.21

Glossary

Terms explained briefly

Dotted words in the text open these explanations directly.

Dendritic cells
Immune cells that pick up parts of pathogens and present them to T cells.
Half-life
The time until half of a substance in the blood has been cleared.
Lyophilisate
Freeze-dried powder. Without water a peptide keeps much longer.
Placebo
A dummy without active ingredient, used for comparison in trials.
Regulatory T cells
T cells that slow down excessive immune reactions.
Sepsis
A life-threatening reaction of the body to an infection with organ failure.
Subcutaneous
Into the fat layer just under the skin.
T cells
White blood cells that recognise infected cells and steer the immune defence.
Thymalfasin
The name of synthetically made Thymosin Alpha-1 as a drug.
Thymus
A gland behind the breastbone where T cells mature. It shrinks with age.
TLR9
Toll-like receptor 9, a sensor of innate immunity for foreign genetic material.

Evidence

Sources

Show all 8 sourcesHide sources 6 Studies1 Trial registry1 Database checked 26 Oct 2026

Studies

  1. ETASS: Thymosin Alpha-1 in severe sepsis, randomised

    Wu et al., Critical Care, 2013

    DOI 10.1186/cc11932 PMID 23327199 NCT00711620
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  2. TESTS: phase 3 trial in sepsis versus placebo

    Wu et al., BMJ, 2025

    DOI 10.1136/bmj-2024-082583 PMID 39814420 NCT02867267
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed, PMC
  3. TRACE: severe pancreatitis versus placebo

    Ke et al., Intensive Care Medicine, 2022

    DOI 10.1007/s00134-022-06745-7 PMID 35713670 NCT02473406
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  4. Large randomised trial in advanced melanoma

    Maio et al., Journal of Clinical Oncology, 2010

    DOI 10.1200/JCO.2009.25.5208 PMID 20194853 NCT00911443
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  5. Review: approval and clinical uses of Thymosin Alpha-1

    Goldstein et al., Expert Opinion on Biological Therapy, 2009

    DOI 10.1517/14712590902911412 PMID 19392576
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  6. Thymosin Alpha-1, dendritic cells and TLR9

    Romani et al., Blood, 2006

    DOI 10.1182/blood-2006-02-004762 PMID 16741252
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed

Trial registry

  1. Trials with thymalfasin on ClinicalTrials.gov

    ClinicalTrials.gov, U.S. National Library of Medicine

    Checked 26 Oct 2026 via ClinicalTrials.gov API v2

Database

  1. Thymalfasin in ChEMBL (phase 3, 28 amino acids)

    ChEMBL, EMBL-EBI (CHEMBL2103979)

    Checked 26 Oct 2026 via ChEMBL

In the shop

Thymosin Alpha-1 in the catalog

Sizes, prices and shipping times are on the product page.

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