The Union Cycliste Internationale (UCU) has announced that it will propose a ban on the use of carbon monoxide (CO) by riders at its next Steering Committee meeting in January.

The UCI wants to officially ban the use of carbon monoxide on medical grounds, but has confirmed that qualified medical personnel can use it within the strict confines of assessing total hemoglobin levels. The gas is not currently on WADA's list of banned substances.

During the 2024 Tour de France, UAE Team Emirates, Visma Lease-a-Bike, and Israel Premier Tech used carbon monoxide rebreather technology at the beginning and end of their high-altitude training camps to test riders' blood levels, as The use of carbon monoxide in professional cycling made headlines when it was revealed by the Escape Collective.

Tadej Pogačar and Jonas Vingegaard at least admitted to being aware of and using rebreathers. Frequent inhalation differs from rebreathing, and the former may enhance aerobic capacity as an alternative or complement to high-altitude training.

It is unclear how UCI would enforce the ban. If carbon monoxide abuse is detected, an approved testing procedure would be required by WADA regulations. Only if evidence of carbon monoxide abuse is uncovered by police or media investigations, or through whistleblowing, could the case come to light.

WADA told Reuters that carbon monoxide abuse may fall under “artificially enhancing the uptake, transport, or delivery of oxygen” on the list of prohibited substances and methods.

“It is not recommended because it is generally accepted to be dangerous to health.”

The Escape Collective confirmed that “there is no hard evidence that any world team is currently using CO inhalation for performance enhancement. However, the UCI took action because of the potential for it to be abused.

The UCI informed teams at the recent UCI World Tour Congress of the current findings regarding the performance effects of repeated carbon monoxide (CO) inhalation; the UCI asked WADA to “take a position” on the use of carbon monoxide for performance enhancement and to “take and UCI President David Lapartient reiterated that position at last week's WADA Executive Committee meeting in Saudi Arabia.

“Exposure to carbon monoxide has been discussed by WADA's Prohibited List Expert Advisory Group on several occasions,” WADA told Reuters.

“There is no general consensus on whether CO has a performance-enhancing effect, and there is currently no sufficient probative data to support that proposition.

This week, UAE Team Emirates confirmed that it will not use carbon monoxide rebreathing to measure athlete performance.

Performance coordinator Jeroen Swart told a small number of media outlets, including Cycling News, that UAE Team Emirates has “completed the process” for the technique. He said it was “an exercise that took 18 months of coordination” to assess the improvement of riders during the high altitude training camp.

The UCI's decision will be made at the next Management Committee meeting, which will take place during the World Cyclocross Championships in Arras, France, on January 31 and February 1, 2025. [Carbon monoxide is an odorless, toxic gas that often causes domestic accidents. Inhaled at low doses and under strict safety conditions, the gas is used in medicine as a tracer to measure lung diffusion of oxygen and total hemoglobin,” the UCI said.

However, when inhaled repeatedly in non-medical situations, it can cause side effects such as headache, fatigue, nausea, vomiting, chest pain, dyspnea, and even loss of consciousness.

“UCI believes that the complete lack of knowledge of these adverse health effects and the long-term effects of repeated inhalation of carbon monoxide justifies a ban on the use of this gas on medical grounds. However, it would continue to be approved for use in medical settings by qualified health care professionals and in the strict context of assessing total hemoglobin levels.