Skip to main content
REMEVi
ENES
What REMEVi offers

TB-500 side effects: human, animal and unknown

What has been reported, what has not been studied, and how to report a reaction.

Nobody has published human side-effect data on TB-500; FDA says it has identified no human exposure data and lacks information on whether it would cause harm in humans. A trial of full-length thymosin beta-4, a different molecule, reported mostly mild effects. Injection-site reactions are possible with any injection. No one can call TB-500 risk-free.

TB-500 is not FDA-approved. Since HHS’s October 2026 interim policy, a state-licensed 503A pharmacy may compound it on a patient-specific prescription under listed conditions.

REMEVi does not currently offer TB-500.

Reported in human studies

None for TB-500. FDA says it has not identified any human exposure data for products containing the thymosin beta-4 fragment sold as TB-500.

The closest human data are for full-length thymosin beta-4: a 2010 randomized, placebo-controlled phase 1 trial in 40 healthy volunteers reported adverse events that were infrequent and mild to moderate, with no dose-limiting toxicity or serious adverse events, at intravenous doses of 42 to 1,260 mg. That is a different molecule and a route the policy does not list.

Reported in animal studies

Animal research on thymosin beta-4 has focused on injury models in skin, cornea and heart rather than on side effects. We found no published animal toxicity study of TB-500 itself. The 2012 horse study measured detection in urine and plasma, not effects.

What is unknown

  • Almost everything about TB-500 in people: short-term effects, effects of repeated use, and long-term effects.
  • Immune reactions: FDA flags possible immunogenicity from aggregation and peptide-related impurities.
  • Interactions with prescription drugs or supplements.
  • Effects in pregnancy, breastfeeding, children and teens.
  • Effects in people with cancer. Thymosin beta-4 research describes effects on cell migration and blood-vessel growth; how that applies to people with an existing tumor has not been studied.

Injection-site effects

Any injection can cause redness, swelling, tenderness, bruising or itching where the needle went in. Spreading redness, warmth, pus or fever can mean infection: contact your provider promptly. Trouble breathing, swelling of the face or throat, or a widespread rash: call 911.

Who should not use TB-500 without talking to a provider first

  • Pregnant, trying to conceive or breastfeeding: there are no human data.
  • Under 18.
  • Active cancer or a history of cancer: tell your provider; this is a discussion point, given the blood-vessel-growth research on thymosin beta-4.
  • A known allergy to TB-500 or any ingredient in the product.
  • Any other medications or supplements: tell your provider about all of them.
  • Competitive athletes, including in equestrian sport: check your sport’s anti-doping rules; TB-500 has been the subject of doping-control testing.

What FDA has said about TB-500

FDA’s page on bulk substances that may present significant safety risks lists the thymosin beta-4 fragment (LKKTETQ), also known as TB-500, among substances previously in Category 2 whose nominations were withdrawn. FDA keeps its concerns on record: possible immunogenicity from aggregation and peptide-related impurities, no human exposure data identified, and missing information on whether it would cause harm in humans.

HHS’s October 2026 policy does not change that. HHS says it does not grant FDA approval or establish clinical safety and effectiveness.

Report a serious reaction

Report serious side effects to your prescriber and to FDA MedWatch, online or at 1-888-463-6332. Under the 2026 policy, compounders must report serious adverse events to MedWatch too.

FDA MedWatch

Is TB-500 safe?

There is no human evidence to answer that. FDA says it has identified no human exposure data for TB-500 and lacks information on whether it would cause harm in humans. A trial of full-length thymosin beta-4, a different molecule, reported mostly mild effects, but that does not transfer. Talk to a licensed provider.

What are the side effects of TB-500?

Nobody has measured them in people: FDA has identified no human exposure data for TB-500. Any injection can cause redness, swelling or bruising at the site, and FDA flags possible immune reactions from aggregation and impurities. Short- and long-term effects in people are unknown. Report serious reactions to FDA MedWatch.

Sources

  1. FDA — Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (content current as of 04/22/2026) (read November 2, 2026)
  2. Ruff et al., Ann N Y Acad Sci 2010 — A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers (read November 2, 2026)
  3. Philp & Kleinman, Ann N Y Acad Sci 2010 — Animal studies with thymosin beta-4 (review) (read November 2, 2026)
  4. Ho et al., J Chromatogr A 2012 — Doping control analysis of TB-500, a synthetic version of an active region of thymosin β4, in equine urine and plasma by LC-MS (read November 2, 2026)
  5. Holland & Knight, Oct 16 2026 — Peptides at a crossroads: what wellness providers need to know (read November 2, 2026)
  6. AJMC (Steinzor), Oct 29 2026 — 5 things to know about HHS’s interim peptide compounding policy (read November 2, 2026)
  7. FDA — MedWatch: The FDA Safety Information and Adverse Event Reporting Program (read November 2, 2026)
  8. Foley & Lardner (Holtz, Beaver, Rosen), National Law Review, Oct 30 2026 — Peptides: HHS announces limited enforcement discretion for compounding six peptides (read November 2, 2026)

Medically reviewed by Linda West-Conforti, RN · CA RN #389453 ·