The World Anti-Doping Agency's 2026 Prohibited List took effect January 1, 2026, having been approved by WADA's Executive Committee in September 2025. The single item that changed from permitted to prohibited is the non-diagnostic use of carbon monoxide, added under the blood-doping section (M1).
Controlled inhalation of small, repeated doses of carbon monoxide can act as a hypoxic-like stimulus that raises endogenous erythropoietin and, over time, total hemoglobin mass, mimicking altitude training. WADA prohibited the non-diagnostic use because of that performance effect and because uncontrolled inhalation of a toxic gas carries a real risk of poisoning.
Legitimate diagnostic uses remain permitted, specifically the measurement of total hemoglobin mass by CO rebreathing and the determination of pulmonary diffusing capacity. The distinction is between a brief measurement protocol and repeated dosing intended to drive adaptation.
The 2026 list also carried mostly clarifications elsewhere: WADA reaffirmed that esters of prohibited anabolic agents are prohibited, added pegmolesatide as an example EPO-mimetic under peptide hormones, and folded cell components such as mitochondria and other organelles into the existing prohibition on cell-based methods.