The World Anti-Doping Agency (Wada) has added the non-diagnostic use of carbon monoxide to its prohibited methods list from next year, following concerns over its misuse.
The gas – which is fatal when inhaled at certain doses – can be used at low doses to measure blood values such as haemoglobin levels in athletes’ blood, but there is concern that repeated use can have performance-enhancing effects.
Controversy erupted last year when an investigation by the website Escape Collective revealed that several teams used carbon monoxide rebreather tools as part of altitude camps.
Several teams, including UAE Team Emirates-XRG – home of world champion and four-time Tour de France winner Tadej Pogacar – and Visma-Lease a Bike said during the 2024 Tour that they used the technique at the beginning and end of altitude camps to measure the effects of training.
At the time, Pogacar said: “You breathe into a balloon for one minute and then you see the haemoglobin mass. It’s a pretty simple test to see how you respond to altitude training. It’s not like we’re breathing exhaust pipes every day from cars.”
There is no suggestion that any team or athlete used the technique for performance enhancement. But a growing body of research suggests that repeated carbon monoxide inhalation can improve an athlete’s aerobic capacity, such as their VO2 max – essentially an athlete’s aerobic ceiling.
The Union Cycliste Internationale (UCI), cycling’s governing body, then moved to ask Wada to ban the technique as a performance enhancement.
It said in a press release: “The UCI clearly asks teams and riders not to use repeated CO inhalation. Only the medical use of a single inhalation of CO in a controlled medical environment could be acceptable.
“The UCI is also officially requesting the World Anti-Doping Agency (WADA) to take a position on the use of this method by athletes.”
The UCI then banned athletes under its own jurisdiction from using it earlier this year, citing health concerns over the long-term impacts of repeatedly inhaling quantities of a poisonous gas. However, it said that its use as a diagnostic tool for measuring haemoglobin mass, under the guidance of a medical professional in a controlled setting, was still permitted.
Wada’s 2026 code, released on Wednesday, follows in the UCI’s footsteps, with the ban now coming from the highest level of anti-doping. It stated in its summary of the changes to the Prohibited List that carbon monoxide “can increase erythropoiesis under certain conditions.”
The 2026 code will still permit its use as a diagnostic method, such as for measuring blood volume. The announcement read: “The use of carbon monoxide for diagnostic purposes, such as total haemoglobin mass measurements or the determination of pulmonary diffusion capacity, is not prohibited.
“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.”
