The UCI Management Committee has formally approved a ban, taking effect on 10 February 2025, on the repeated inhalation of carbon monoxide.

What does this ban change? The regulations that will implement the Management Committee’s decision are yet to be released, however the press release announcing the ban states as follows:

The new regulation forbids the possession, outside a medical facility, of commercially available CO re-breathing systems connected to oxygen and CO cylinders. This ban applies to all licence-holders, teams and/or bodies subject to the UCI Regulations and to anyone else who might possess such equipment on behalf of riders or teams.

The inhalation of CO will remain authorised within a medical facility and under the responsibility of a medical professional experienced in the manipulation of this gas for medical reasons and in line with the following restrictions: only one CO inhalation to measure total Hb mass will be permitted. A second CO inhalation will only be authorised two weeks after the initial Hb measurement.

For riders in UCI WorldTeams, UCI Women’s WorldTeams and UCI ProTeams, any CO inhalation for the purpose of determining total Hb mass must be recorded in the medical file established for each athlete, in compliance with Articles 13.3.020 to 13.3.026 of the UCI Medical Rules.

The UCI’s ban is independent of the World Anti-Doping Code and the UCI Anti-doping Regulations, however the UCI has officially requested the World Anti-Doping Agency (WADA) to take position on the repeated use of CO in and out of competition.

Breaking that down, the proposed rule change by the UCI largely preserves the status quo. Subject to a few qualifiers, no ban has been imposed on the usage of carbon monoxide rebreathers for measurement purposes. The qualifiers are that the initial inhalation is only done once, and the second inhalation takes place two weeks after the first (presumably, at least two weeks). Any rebreather use in this manner must be logged in the rider’s medical file. Essentially, this is how rebreathers are currently being used by teams to monitor the effectiveness of altitude training.

In as much as there is anything ‘new’ in this announcement:

• It makes clear that the repeated use of carbon monoxide to manipulate blood values is prohibited. This was likely already covered by prohibited method M1 in the 2025 Prohibited List (the general prohibition on manipulation of blood and blood components), but this rule change provides additional clarity on the position from the UCI’s perspective, and is expressed to be “independent of the World Anti-Doping Code and the UCI Anti-Doping Regulations”.
• The change seeks to restrict the settings in which teams can own (directly or indirectly) and use rebreather devices to “medical facilities”. What constitutes a medical facility is open to interpretation, but the intention seems to be to ensure that any rebreather use is in a controlled environment.

So, contrary to some attention-grabbing headlines, carbon monoxide rebreathers have not been banned entirely – they have just been explicitly restricted use as a measurement tool to assess the effects of altitude camps. Use, technically even repeated use, of carbon monoxide is permitted, provided that those uses are spaced sufficiently far apart.

Nonetheless, this is a welcome change by the UCI, bringing clarity to the position that repeated inhalation of the gas for performance-enhancing purposes (as Jonas Vingegaard recently claimed was happening in some teams) is prohibited.

Words: Nick Williams