The World Anti-Doping Agency has followed the UCI’s crackdown on carbon monoxide rebreathing and added the use of the gas as a performance-enhancer to its prohibited list, starting from 2026.
The non-diagnostic use has been added to the list, as “it can increase erythropoiesis under certain conditions,” WADA has stated.
Erythropoiesis, or the production of oxygen-carrying red blood cells, can be stimulated by the inhalation of carbon monoxide. However, in sufficient doses, the inhalation of this gas can be fatal, raising safety fears about riders potentially risking their health for performance gains.
This stimulates the type of hypoxia, or lack of oxygen, that would occur at high altitude levels. Training camps in high altitude have become standard for professional cyclists, as hypoxic exercise improves the body’s ability to use oxygen during exercise.
The gas can still be used as a diagnostic tool. For example, it could be used during altitude camp to track a rider’s progress over a block of training, as it provides an accurate means of measuring haemoglobin.
“Carbon monoxide for diagnostic purposes, such as total haemoglobin mass measurements or the determination of pulmonary diffusion capacity, is not prohibited,” stated WADA in the summary of major modifications to the 2026 Prohibited List.
“The current wording was chosen to differentiate between illicit use and the intake resulting from natural combustion processes (e.g. smoking), the environment (e.g. exhaust gases) or diagnostic procedures.”
This follows controversy after a report by the Escape Collective website, which stated that UAE Team Emirates, Visma-Lease a Bike, and Israel-Premier Tech allegedly used carbon monoxide during the 2024 Tour de France.
The teams of Jonas Vingegaard and Tadej Pogačar confirmed that they had access to the equipment for testing, but any alternative use has not been proven.
Tadej Pogačar and Jonas Vingegaard, 2024 Tour de France (credit: ASO/Charly Lopez)
Both Pogačar and Vingegaard admitted at the 2024 Tour de France that they had previously used carbon monoxide rebreathers, but within the context of testing.
“It’s to measure how much haemoglobin you have in your blood. There is nothing suspicious about it,” said Jonas Vingegaard.
“They [the doctors] say that they send something into the lungs that is similar to smoking a cigarette. We measure the day we get to our high-altitude camp and then [on] the day we go back down. Then we see the difference in how much haemoglobin is built up. There is nothing more to it.”
Despite the teams denying its exploitation for direct performance-enhancing gain, former DSM-Firmenich PostNL climber Romain Bardet believed it could be used to enhance performance.
“We see the studies. Anything is possible. I have never heard of anything but at the same time, I would not be surprised.
“There is so much research being done with the idea of optimising performance. Ten years ago, there were lots of promises about altitude. Everyone was getting involved, it was a bit of a panacea. We know exactly where it can take us.
“It is not surprising that there are certain researchers, certain teams, certain cyclists who are looking elsewhere. There will always be the desire to seek competitive advantages.”
WADA’s statement follows the UCI in February announcing a ban on the “repeated inhalation” of carbon monoxide “outside a medical facility”, claiming that the controversial method of measuring an athlete’s haemoglobin can cause chronic health problems if used frequently.
Cycling’s governing body proposed its plans for the ban in December last year, and the new regulation means that teams and riders are forbidden from being in the possession of commercially available carbon monoxide rebreathing devices connected to oxygen and carbon monoxide cylinders.