TB-500 vs Thymosin Alpha-1: Different Molecules
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TB-500 vs thymosin alpha-1: how do they differ?

Structure · Human trials · Status

Short answer: They share a name but are different molecules. TB-500 is a 7-amino-acid fragment of thymosin beta-4 with no documented human effects.1 Thymosin alpha-1 (thymalfasin) is a separate 28-amino-acid peptide, approved in other countries for hepatitis B but not in the US.2 It has many human trials, though results are mixed; a 1,106-person sepsis trial found no mortality benefit.3

How do TB-500 and thymosin alpha-1 compare side by side?

From published studies, FDA compounding pages and the 2026 WADA List. Neither has a US label.
TB-500Thymosin alpha-1 (thymalfasin)
What it isAc-LKKTETQ, a 7-amino-acid fragment of thymosin beta-4128-amino-acid peptide first found in the thymus2
Approval statusNot approved anywhereApproved by several regulators outside the US for hepatitis B and as a vaccine enhancer;2 not FDA approved
Main proposed useTissue repair and wound healingImmune modulation (T-cell function)4
Human studiesNone for TB-500 itself; trials exist only for full-length thymosin beta-45Many, incl. 10 hepatitis B RCTs (1,349 people)6 and a phase 3 sepsis trial3
Doses in human studiesNone1.6 mg under the skin twice weekly for hepatitis;4 every 12 hours for 7 days in sepsis3
Half-lifeNo value for TB-500. Full-length thymosin beta-4 IV: 0.5 to 2.08 hours5about 2 hours4
Time to peak (Tmax)No human dataWithin about 2 hours4
FDA compounding statusNominated but withdrawn; FDA found no human exposure data7Nominated but withdrawn; FDA cites immunogenicity risk7
SportWADA S2.3 (thymosin beta-4 and derivatives, e.g. TB-500)8Not named on the 2026 List8

Reviewed . Half-life figures are shown only where the value Dose Track uses agrees with the cited source.

Why do they share a name?

The shared name is historical; they are different molecules. Thymosin alpha-1 is 28 amino acids long.2 TB-500 is not a whole protein at all: it is the 7-amino-acid sequence Ac-LKKTETQ taken from thymosin beta-4, and a 2024 doping-control paper notes its own biological effects have not been documented.1 Results for one say nothing about the other.

What do the thymosin alpha-1 trials show?

  • Sepsis (TESTS, 2025): 1,106 adults in 22 Chinese centers, injections every 12 hours for 7 days. 28-day mortality was 23.4% vs 24.1% on placebo, with no clear benefit.3
  • Hepatitis B (Cochrane, 2026): 10 randomized trials with 1,349 people. The reviewers rated the evidence very low certainty for most outcomes and said they are not sure whether it reduces death or serious harm.6
  • Pharmacokinetics: a 2001 review reports peak levels within about 2 hours and a half-life of about 2 hours, with injection-site irritation as the main side effect.4

For TB-500, the only human trials are of full-length thymosin beta-4, given IV, as eye drops or as a gel.59 These are study protocols, not personalized advice; confirm any dosing with your prescriber.

What is their US status?

Neither is FDA approved. Both are on FDA's list of compounding bulk substances that were in Category 2 and then withdrawn by their nominators. FDA says it found no human exposure data for the TB-500 fragment, and that safety information for thymosin alpha-1 is inadequate to judge its risks.7 FDA's July 2026 advisory committee reviewed TB-500 for wound healing; thymosin alpha-1 was not on that agenda.10

This page summarizes labels and published studies. It is not personalized medical advice; confirm any dose or change with your prescriber.
BPC-157 vs TB-500: what does the evidence actually show?Mostly preclinical evidence, 2026 FDA status BPC-157 vs GHK-Cu: what does the evidence show?Injected pilot data vs mostly topical skin studies

Frequently asked questions

Is TB-500 the same as thymosin alpha-1?+
No. TB-500 is a 7-amino-acid fragment of thymosin beta-4. Thymosin alpha-1 is a different 28-amino-acid peptide.12
Is thymosin alpha-1 approved anywhere?+
Yes, outside the US. Thymalfasin has been approved by several regulators for hepatitis B and to boost vaccine response in people with weak immune systems. It is not FDA approved.2
What is the half-life of thymosin alpha-1?+
About 2 hours, with peak levels within about 2 hours of an injection, per a 2001 review.4
Did thymosin alpha-1 help in sepsis?+
Not in the phase 3 TESTS trial: 28-day mortality was 23.4% vs 24.1% on placebo.3
Can I track TB-500 and thymosin alpha-1 in Dose Track?+
Yes. Both are built in, with reconstitution math so each amount shows in syringe units, and reminders.

Sources

  1. Rahaman KA, et al. Detection of TB-500 (Ac-LKKTETQ) and its metabolites for doping control. J Chromatogr B. 2024.
  2. Mao L, et al. Thymosin alpha 1: reimagine its broader applications in the immuno-oncology era. Int Immunopharmacol. 2023.
  3. Wu J, et al. Efficacy and safety of thymosin alpha 1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ. 2025;388:e082583.
  4. Ancell CD, et al. Thymosin alpha-1. Am J Health Syst Pharm. 2001;58:879-85.
  5. Wang X, et al. A first-in-human phase I study of recombinant human thymosin beta-4 (NL005) in healthy volunteers. J Cell Mol Med. 2021.
  6. Naing C, et al. Thymosin alpha 1 for people with chronic hepatitis B. Cochrane Database Syst Rev. 2026;9:CD014610.
  7. FDA. Certain bulk drug substances for use in compounding that may present significant safety risks (Category 2 and nominated-but-withdrawn lists). Updated April 2026.
  8. World Anti-Doping Agency. The 2026 Prohibited List, in force January 1, 2026 (English text as published in the Dutch Treaty Series, Tractatenblad 2026, 25).
  9. Ruff D, et al. A randomized, placebo-controlled, phase 1 study of intravenous thymosin beta 4 in healthy volunteers. Ann N Y Acad Sci. 2010.
  10. FDA. Pharmacy Compounding Advisory Committee meeting, July 23-24, 2026.

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