At a glance: TB-500 is a lab-made seven-amino-acid fragment of thymosin beta-4, a natural repair protein. It is popular for muscle, tendon and injury recovery, but FDA's 2026 review found no human studies of TB-500 at all. The human trials often cited used the full thymosin beta-4 protein, and even those had mixed results. TB-500 is not FDA-approved, an advisory panel voted 8 to 6 in July 2026 to recommend it for compounding against FDA staff advice, and it is banned in sport.
What is TB-500?
TB-500 is a synthetic peptide with the sequence Ac-LKKTETQ: amino acids 17 to 23 of thymosin beta-4 (TB4), with an acetyl group added to one end. Thymosin beta-4 is a natural 43-amino-acid protein found in almost all cells, where it helps control actin, the protein cells use to move and change shape.
Sellers often use "TB-500" and "thymosin beta-4" interchangeably, but they are different molecules. Research on the full protein does not automatically apply to the fragment. FDA also notes that "TB-500" is not an official drug name.
How does TB-500 work?
The LKKTETQ stretch is thought to be the part of thymosin beta-4 that binds actin. Based mostly on studies of the full protein, the proposed effects are:
- Cell movement: helping repair cells migrate into damaged tissue
- New blood vessels: supporting angiogenesis, which brings blood supply to healing areas
- Calming inflammation: lowering inflammatory signals in lab models
- Uncertain for the fragment: in one lab study cited by FDA, TB-500 itself did not significantly speed closure of scratch "wounds" in skin cells
What the research shows so far
| Study | What was tested | Main finding |
|---|---|---|
| Human studies of TB-500 | None | FDA found no clinical trials, pharmacokinetic studies or case reports by any route |
| RGN-137 phase 2 (2009) | Full thymosin beta-4 gel in 72 people with leg (venous stasis) ulcers | Safe and well tolerated; healing differences vs placebo were not statistically significant |
| SEER-1 phase 3 (RGN-259) | Full thymosin beta-4 eye drops in 18 people with a nerve-related corneal disorder | 6 of 10 healed vs 1 of 8 on placebo, but narrowly missed its main statistical goal |
| Animal studies | Mostly full thymosin beta-4 or the non-acetylated fragment, in mice and rats | Faster wound, skin, heart and eye repair; FDA says these cannot be assumed to apply to TB-500 |
| Horse study | TB-500 injected under the skin | Very low blood levels that became unmeasurable within 6 to 10 hours |
FDA also found no standard toxicology studies (repeat-dose, genetic, reproductive or cancer) for TB-500.
Why it gets attention
- Injury recovery: promoted for muscle strains, tendon and ligament injuries, and joint pain
- Athletes and veterinary roots: long used in horse racing and among athletes, which led to anti-doping bans
- The "Wolverine stack": often paired with BPC-157, a combination that has not been tested in controlled human trials
- The 2026 FDA vote, which put it among six peptides recommended for compounding
How it is used
TB-500 is sold as powder for injection under the skin or into muscle, almost always labeled "for research use only." FDA found no record of US pharmacies compounding it. Online protocols vary widely, but no dose has been established in human studies. This page does not provide dosing guidance.
What about side effects?
Because TB-500 has never been studied in people, its side effects and their frequency are unknown. Users report injection-site reactions, tiredness and lightheadedness.
- Immune reactions: FDA's main concern is immunogenicity, made worse by peptide clumping and impurities in injectable products.
- Product quality: FDA found no certificates of analysis testing identity, endotoxins or aggregates. Research products may be mislabeled or non-sterile.
- Cancer questions: because thymosin beta-4 promotes cell movement and blood vessel growth, some researchers have raised concerns about effects on existing tumors. This has not been studied for TB-500.
- Pregnancy and breastfeeding: not studied.
Regulatory status
- Not FDA-approved for any use.
- In April 2026 FDA removed TB-500 from its "Category 2" safety-concern list after its nomination was withdrawn. That was not a safety finding.
- FDA reviewed it for wound healing and recommended against adding it to the compounding list, citing poor characterization, no human data and immune-reaction risk, and noting that approved wound treatments exist.
- On July 23, 2026 the advisory committee voted 8 to 6, with 1 abstention, to recommend it anyway. The vote is non-binding, and formal rulemaking would be needed before compounding is allowed.
- TB-500 is prohibited at all times by the World Anti-Doping Agency.
TB-500 vs thymosin beta-4
| TB-500 | Thymosin beta-4 (full protein) | |
|---|---|---|
| Size | 7 amino acids (acetylated fragment) | 43 amino acids |
| Human trials | None | Small phase 2 and 3 trials (eye drops, wound gel) |
| Trial results | Not applicable | Safe, but main efficacy goals not met |
| US status | Not approved; advisory vote in favor of compounding | Not approved; investigational |
The bottom line
TB-500 borrows its reputation from thymosin beta-4, a real repair protein with interesting animal results and a few modest human trials. But TB-500 itself has never been tested in people, FDA found basic quality and safety data missing, and the 2026 advisory vote did not approve it. Anyone with a lingering injury should see a sports medicine clinician about proven treatments.
Frequently asked questions
What is TB-500?
A synthetic version of the active region of thymosin beta-4, a protein found in most of the body’s cells that helps them move and rebuild.
How is TB-500 taken?
Injection in animal studies; no established human route.
Is TB-500 FDA approved?
Not approved; on WADA’s prohibited list.
That means no regulator has reviewed its safety, effectiveness or manufacturing quality for this use.
What has research shown about TB-500?
- Wound healing and new blood vessel growth in animal studies.
- Heart and muscle tissue repair in animal models.
What side effects have been reported?
- Not characterised in humans
Serious or less common risks are listed in the Side Effects section above.
What is still unknown about its safety?
Most of it. TB-500 has not been through the trials that establish long-term safety in people, and products sold online are made by unregulated labs. Independent testing of online peptides has repeatedly found contents that do not match the label.
References
- FDA: Evaluation of TB-500 and TB-500 acetate for the 503A bulks list (July 2026 PCAC briefing). View source
- Rite Aid: TB-500 overview. View source
- AJMC: FDA panel backs 6 peptides for compounding (July 2026). View source
- Fierce Biotech: RegeneRx reports phase II venous stasis trial results (RGN-137, 2009). View source
- American Pharmaceutical Review: RegeneRx joint venture announces neurotrophic keratopathy trial results (SEER-1, RGN-259). View source