WADA Adds Non-Diagnostic Carbon Monoxide Use to Prohibited Methods in 2026 Anti-Doping List

The short version: starting January 1, 2026, athletes cannot use carbon monoxide to artificially boost their endurance. The World Anti-Doping Agency (WADA) has officially added the non-diagnostic use of carbon monoxide to its Prohibited List. For athletes across all disciplines—from Tour de France cyclists to mixed martial artists looking to build their gas tank—repeatedly inhaling the toxic gas to mimic altitude training is now a banned blood manipulation tactic.[1][3]

The ruling addresses a controversial physiological loophole that gained mainstream attention during the 2024 professional cycling season. Several elite teams were found using carbon monoxide rebreathers. While the teams insisted the devices were strictly for measuring blood values, the revelation sparked immediate concern among sports scientists. The fear was that the method could be weaponized to force the body into producing more red blood cells without the athlete ever leaving sea level.[2][7]

To understand why this matters for your own training, it helps to look at the underlying physiology. Carbon monoxide binds to hemoglobin—the protein in your red blood cells that carries oxygen—with an affinity roughly 200 times stronger than oxygen itself. When inhaled in controlled, repeated doses, it crowds out oxygen and induces a state of artificial hypoxia.[5][6]

Your body, sensing that it is starved of oxygen, responds exactly as it would at high altitude: it releases erythropoietin (EPO). This hormone stimulates the production of new red blood cells. For a combat sports athlete facing a grueling five-round fight, a higher red blood cell count translates directly to a higher VO2 max, better oxygen delivery to working muscles, and significantly delayed fatigue.[4][6]

However, the line between a performance-enhancing dose and a highly toxic one is notoriously thin. Carbon monoxide is a poisonous gas; miscalculating the dose can lead to severe confusion, rapid heart rate, organ damage, or death. Recognizing these severe health risks, the Union Cycliste Internationale (UCI) lobbied WADA to implement a comprehensive ban before the practice could spread to other endurance and combat sports.[3][5]

Under the new M1.4 classification in the 2026 WADA code, the non-diagnostic use of carbon monoxide is strictly prohibited. WADA's medical committee concluded that while the gas can indeed increase erythropoiesis under certain conditions, the potential for fatal miscalculation far outweighs any theoretical athletic benefit. The message is clear: the risks of artificial hypoxia are not worth the physiological adaptations.[1][4]

Crucially, WADA has carved out a specific, practical exemption for diagnostic use. Sports scientists and team physicians can still employ single-dose carbon monoxide rebreathing tests to accurately measure an athlete's total hemoglobin mass. This allows coaches to safely track whether a legitimate high-altitude training camp is actually working, without crossing the line into active doping.[1][2]

The diagnostic test involves inhaling a small, precise volume of carbon monoxide, temporarily raising the blood's CO concentration to roughly six percent—comparable to the levels found in a heavy smoker. Because the gas clears the system within 24 hours, a single diagnostic application poses minimal long-term risk. By drawing a hard line between measurement and manipulation, WADA is protecting athlete safety while preserving a valuable tool for legitimate sports science.[2][7]