Peptide · Thymosin beta-4 fragment
TB-500 (thymosin beta-4 fragment)
A synthetic fragment related to thymosin beta-4, sold as a research chemical.
Regulatory gapNeither barred as a safety risk nor cleared for compounding.
- Legal status · US
- Regulatory gap
- Evidence in people
- Molecule
- Thymosin beta-4 fragment
- In sport
- Prohibited (WADA)
- Status checked
Regulatory status · United States
This describes the position in the United States. Rules in Bulgaria differ; an approved peptide medicine there is in its national register.
No human-use authorisation in any major market. Removed from the FDA’s Category 2 list in April 2026, which does not make it eligible for compounding. On 23–24 July 2026 the FDA’s Pharmacy Compounding Advisory Committee voted to recommend adding it to the 503A Bulks List, against the recommendation of FDA staff. An advisory vote changes nothing by itself: the FDA must still act, through rulemaking, before it can lawfully be compounded from bulk.
Prohibited at all times under WADA class S2 — thymosin beta-4 and its derivatives are named.
What changed, and when
Removed from 503A Category 2. Not added to the Bulks List.
Advisory committee votes to recommend it for the Bulks List.
What to be careful about
Banned in competition. Human evidence is absent; what circulates online are animal studies and vendor claims.
Why there is no dosing information here
There is no authorised human dose to report. Any figure printed here would come from a vendor or a forum, and would look exactly like one taken from an approved label — which is the specific confusion that makes this category dangerous.
Sources
- FDA — bulk drug substances that may present significant safety risks (Category 2), page current as of 22 April 2026
- FDA — Pharmacy Compounding Advisory Committee, 23–24 July 2026
- WADA Prohibited List
Regulatory positions change. This page states the date it describes, and nothing on it is legal or medical advice.