Regulatory status & anti-doping

Legal to buy, not approved, and banned in sport

TB-500’s legal picture is easy to misread. It is sold as a "research chemical", it is not FDA-approved for any use, it was placed on the FDA’s 503A category 2 compounding-restriction list on September 29, 2023 (listed as "Thymosin beta-4, fragment (LKKTETQ)") and then removed from that list, with 11 other peptides, in April 2026 (removal is not approval, and it is still not on the authorized 503A bulks list; on July 23, 2026 the Pharmacy Compounding Advisory Committee voted, against the FDA review team’s own written recommendation, to recommend adding TB-500 to that list, with reporting describing the margins across the meeting as narrow and giving no vote count for TB-500 itself, but a committee vote is advice, not a decision, and adding the peptides to the list would still have to go through a lengthy public rulemaking process), and it has been named on the WADA prohibited list since 2018. The marketed fragment was analytically characterized in 2012, and a validated equine plasma method covering it followed in 2013.

This unit maps the jurisdictions, the regulatory timeline, the anti-doping reality, and the gap between "legal to purchase" and "safe or approved".