What FDA has said
FDA’s page on bulk substances that may present significant safety risks in compounding says of “thymosin beta-4, fragment (LKKTETQ), also known as TB-500”: it may pose a risk of immunogenicity for certain routes because of potential aggregation and peptide-related impurities; FDA has not identified any human exposure data for products containing it, and lacks important information, including whether it would cause harm in humans [1].
In the page’s version of 22 April 2026, TB-500 appears in the table of substances whose nominations were withdrawn by the nominators. That is not an approval [1].
Why thymosin beta-4 studies are not the same thing
Full-length thymosin beta-4 has been studied in people in specific, controlled forms: for example as eye drops in a placebo-controlled phase II trial in dry eye, and as a recombinant protein in patients with acute heart attack. These involve a different molecule, different routes and supervised clinical settings; their results say nothing about the side effects of products sold as TB-500 [3][4].
A 2026 sports-medicine review (Mendias et al.), which covers TB-500, notes that rigorous human safety data for such unapproved peptides are scarce and that there is potential for serious harm [2].
PepLabo does not recommend, sell or endorse this substance. It is a tracking app: it records what you tell it and does not tell you what to take.
When to get help
| Sign | Who to contact | How fast | Source |
|---|---|---|---|
| Swelling of the lips, tongue, face or throat, struggling to breathe or swallow, or fainting | Emergency services: anaphylaxis needs medical attention right away. | Emergency | MedlinePlus [5] |
| Painful, red, tender or swollen skin at an injection site, especially with fever or chills | A doctor, the same day (signs MedlinePlus lists for a skin infection). | Today | MedlinePlus [6] |
| Any new symptom that worries you after using TB-500 | A doctor. Bring the product and anything written on it: there is no label that lists expected side effects. | Today | FDA: no or limited safety information [1] |
| Mild symptoms you are keeping track of | Your doctor at your next appointment; a dated log helps. | At your next appointment | FDA: no or limited safety information [1] |
