WADA Adds Non-Diagnostic Carbon Monoxide Use to Prohibited Methods for 2026 List

During the 2024 Tour de France, a startling revelation rippled through the professional cycling peloton: some of the world's top teams were utilizing carbon monoxide rebreathers. While the teams insisted the devices were strictly for measuring blood values, the disclosure raised immediate alarms about a new frontier in performance enhancement. Now, the World Anti-Doping Agency (WADA) has officially closed the loophole.[3][4][7]

Starting January 1, 2026, the non-diagnostic use of carbon monoxide will be explicitly prohibited across all WADA-compliant sports. The ruling, published in the agency's 2026 Prohibited List, categorizes the practice under section M1.4, which governs the manipulation of blood and blood components. It marks a decisive line in the sand against a method that blends cutting-edge sports science with inherent physical risk.[1][2][5]

To understand why an athlete would intentionally inhale a toxic gas, we have to look at how the body adapts to stress. Carbon monoxide binds to hemoglobin—the protein in red blood cells that carries oxygen—roughly 200 times more strongly than oxygen does. When inhaled in small, carefully controlled doses, it temporarily displaces oxygen, creating a state of artificial hypoxia, or oxygen deprivation, within the bloodstream.[3][5][8]

This hypoxic stress acts as a powerful biological trigger. It signals the kidneys to release erythropoietin (EPO), a hormone that stimulates the bone marrow to manufacture more red blood cells. A higher volume of red blood cells directly translates to a greater oxygen-carrying capacity, which is the holy grail for endurance athletes looking to boost their VO2 max and sustain aerobic efforts for longer periods.[3][5]

In essence, a carbon monoxide rebreather attempts to mimic the physiological adaptations of a high-altitude training camp. Instead of spending weeks living on a mountain to naturally stimulate red blood cell production, an athlete could theoretically achieve similar blood-building effects through repeated, controlled inhalations of the gas at sea level.[5][8]

However, the line between a performance-enhancing micro-dose and a life-threatening exposure is perilously thin. Carbon monoxide is an odorless, colorless gas responsible for thousands of accidental poisoning deaths annually. Unregulated or repeated inhalation can lead to severe tissue damage, neurological impairment, and death. WADA’s decision to ban the practice was driven as much by the clear health risks as by the potential for unfair performance gains.[4][6][8]

Crucially, WADA’s new regulation makes a careful distinction between performance enhancement and legitimate medical science. The 2026 code still permits the use of carbon monoxide for diagnostic purposes. A single inhalation of the gas, administered in a controlled clinical setting by medical professionals, remains a highly accurate way to measure an athlete's total hemoglobin mass or pulmonary diffusion capacity.[1][2][6]

This diagnostic exception aligns with the defense offered by professional cycling teams when the practice first came to light. Teams like Visma-Lease a Bike and UAE Team Emirates maintained that they only used the rebreathers to measure the effectiveness of their traditional altitude camps, tracking how much hemoglobin was built up before and after the trips. They firmly denied using repeated inhalations to artificially drive blood cell production.[3][6][7]

The push for a formal ban originated within cycling itself. Recognizing the potential for abuse and the severe health implications, the Union Cycliste Internationale (UCI) banned the repeated inhalation of carbon monoxide in early 2025. The UCI then formally requested that WADA take a definitive stance, leading to the global prohibition that will take effect next year.[4][6][7]

The WADA ruling is significant because it prevents the practice from proliferating into other endurance disciplines. Had carbon monoxide rebreathing remained in a regulatory gray area, it could have easily been marketed to marathon runners, triathletes, and amateur competitors as a convenient shortcut to altitude gains. The ban ensures that this risky method will not become a normalized part of endurance training culture.[5]

Beyond carbon monoxide, the 2026 Prohibited List introduces several other notable updates. WADA has clarified its stance on blood withdrawal, stating that the act of removing blood is prohibited even if it is not reinfused, closing a technical loophole. The agency also expanded its definition of gene and cell doping to explicitly ban the manipulation of cell components, such as mitochondria and ribosomes.[1][2]

For everyday athletes and fitness enthusiasts, the WADA update offers a reassuring reminder about the boundaries of healthy training. While elite sports science will always search for marginal gains, true endurance is built through consistent effort, proper recovery, and safe, proven methods. There are no healthy shortcuts that involve inhaling toxic substances, and the governing bodies of sport have ensured that the playing field remains focused on human effort rather than hazardous chemical manipulation.[5]