TB-500: Side Effects, Evidence, Legality and More, Answered

Anti-doping chemists identified this acetylated fragment in a product sold as TB-500 ⁵. A horse doping laboratory described the same key ingredient in a veterinary TB-500 preparation ⁶.

FDA noted that TB-500 is a common name, not an official drug name ¹. Different salts and molecules have been sold under it ¹. See the TB-500 reference page for the full record.

FDA explained that acetylation changes a peptide's charge, size and behaviour ¹. So even findings on the plain seven-residue fragment do not transfer directly to TB-500 ¹.

Online sources often use the two names interchangeably. Our article on the thymosin family explains how the related molecules differ.

Thymosin beta-4 is a main protein that holds actin, a building block of the cell skeleton ¹¹. Reviews link the full protein to blood vessel growth and repair, though its mechanisms remain unclear ¹².

In the same cell assay, a breakdown product of TB-500 produced a small but significant effect ¹. Whether TB-500 acts through such metabolites is unknown ¹.

In a 2026 rat Achilles tendon study, TB-500 alone improved tendon strength compared with untreated controls ¹³. In aged mice, the full protein and a non-acetylated version of the fragment were linked to faster skin wound closure ⁷.

Claims of special effects for men or women have no study behind them. Our guide on why so much peptide evidence comes from animals explains how to weigh such results.

The rat study randomised animals to control, BPC-157, TB-500 or both ¹³. TB-500 alone showed a significant biomechanical difference from control, and the pair together added nothing ¹³. The authors called the study exploratory ¹³.

Animal tendon results do not show what happens in human injuries.

In the heart-attack trial of 96 patients, recombinant thymosin beta-4 did not significantly change infarcted area overall versus placebo ¹⁰. The authors reported a difference only in a subgroup dosed early after the procedure ¹⁰.

A review links the full protein to blood vessel development and repair in animal models ¹². None of this has been shown for TB-500 in humans.

Being on WADA's list is not evidence that it builds muscle ⁴. FDA found no human data for TB-500 at all ¹.

In fibroblast cells, TB-500 did not differ from a blank solution in wound closure ¹. In rats, it improved maximum load to failure of a repaired tendon ¹³.

Human trials with results used the full thymosin beta-4 protein instead. In a dry eye trial of its eye drops, neither main measure beat placebo ⁹.

In a placebo-controlled study of intravenous full-length thymosin beta-4 in 40 healthy volunteers, adverse events were infrequent and mild or moderate ⁸. That is a different molecule from TB-500 ¹.

FDA's BPC-157 briefing describes darkened skin and gums after use of a research-labelled product combining TB-500 and BPC-157, which recurred on re-use ¹⁶. FDA judged the reaction likely due to that product but could not say which peptide caused it ¹⁶.

FDA stated that toxicity studies of TB-500 were not submitted or identified ¹. Forum reports cannot be checked and are not used here.

FDA also reported that one nomination listed a chemical formula that matched neither the free base nor the acetate salt ¹. That illustrates how uncertain product identity can be.

FDA found no dose-response data for TB-500 ¹. For what human studies did and did not report, see TB-500 dosage in human studies.

Questions about timing, taking it daily or on an empty stomach have no studied answer ¹.

Most peptides are broken down in the gut. Our guide on why most peptides are injected explains the problem ¹.

A horse study detected the parent peptide and its metabolites after administration of a veterinary TB-500 product ⁶. A later method detected acetylated LKKTETQ among seven peptides in horse plasma ¹⁵.

Human half-life is unknown because FDA found no human exposure data ¹.

FDA's Pharmacy Compounding Advisory Committee discussed TB-500 on July 23, 2026, with wound healing as the use evaluated ³. The committee voted on whether it should be placed on the 503A list ³. FDA has not published minutes or announced a decision, and the 503A list is unchanged ³.

FDA staff's briefing proposed not adding it, citing missing characterization, history-of-use and human data ¹. A staff briefing is input to the committee, not FDA's final word. FDA lists TB-500 among substances whose nominations were withdrawn ².

A certificate should state which molecule is present: Ac-LKKTETQ, the plain fragment or the full protein ¹. See how to read a certificate of analysis and peptide legality in the US.

WADA lists TB-500 as a derivative of thymosin beta-4 ^1,4. Tests to detect it were developed by doping laboratories ^5,6. See peptides and sport.

Neither has a controlled human trial with results. See the full table in BPC-157 vs TB-500 ¹³.

The full answer, including injury questions and the "Wolverine" name, is in BPC-157 and TB-500 together: questions answered ¹³. The evidence summary is on the BPC-157 + TB-500 combination page.

Horse studies focused on detecting TB-500 in doping control, not on treatment ^6,15. For the human and animal evidence, see the TB-500 reference page.