WADA Bans Non-Diagnostic Carbon Monoxide Use and Tightens Asthma Drug Rules in 2026 Prohibited List

The World Anti-Doping Agency has officially enacted its 2026 Prohibited List, introducing sweeping changes that target the bleeding edge of sports science. Chief among the updates is a highly anticipated restriction on carbon monoxide rebreathing, a controversial practice that recently swept through the elite echelons of professional cycling.[1]

The updated code also tightens the regulatory net around asthma medications, designer peptides, and the microscopic components of human cells. By closing these loopholes, regulators are attempting to draw a definitive line between legitimate medical diagnostics and artificial performance enhancement, ensuring a level playing field across endurance sports.[2]

The most high-profile addition to the 2026 list is the classification of non-diagnostic carbon monoxide use as a prohibited method under section M1.4. Carbon monoxide is a toxic, odorless gas that can be fatal in high doses, but in the world of endurance sports, it has become a sophisticated tool for manipulating human physiology.[1]

The controversy reached a boiling point during the 2024 Tour de France, when reports emerged that top-tier cycling teams were utilizing carbon monoxide rebreather devices during high-altitude training camps. The teams maintained that they were only using the gas for diagnostic purposes—specifically, to measure total hemoglobin mass and verify whether their grueling altitude training was actually working.

To understand the debate, one must look at the mechanism of carbon monoxide in the human bloodstream. The gas binds to hemoglobin—the protein responsible for carrying oxygen—with an affinity roughly 200 times stronger than oxygen itself. When an athlete inhales a precise, small dose of the gas, it temporarily displaces oxygen, creating a state of artificial hypoxia, or oxygen deprivation.

In a diagnostic setting, sports scientists can measure the concentration of carbon monoxide in the blood to accurately calculate an athlete's total red blood cell volume. However, repeated inhalation of the gas does more than just measure blood metrics; the resulting hypoxia actively stimulates the kidneys to release erythropoietin, or EPO.[2]

This natural surge in EPO triggers erythropoiesis, the biological production of new red blood cells. By repeatedly inhaling carbon monoxide, an athlete can theoretically replicate the blood-boosting benefits of a weeks-long high-altitude training camp without ever leaving sea level, gaining a massive aerobic advantage.

Recognizing the dual-use nature of the gas, the World Anti-Doping Agency opted for a nuanced restriction rather than a blanket ban. Under the 2026 rules, the use of carbon monoxide for diagnostic purposes—such as a single inhalation to measure pulmonary diffusion capacity or hemoglobin mass—remains entirely legal when conducted under strict medical supervision.[1][2]

What is now strictly prohibited is the repeated, non-diagnostic inhalation of the gas designed to artificially induce hypoxia and stimulate red blood cell production. The Union Cycliste Internationale, cycling's governing body, had previously urged regulators to take this exact stance, citing both the performance-enhancing potential and the severe health risks of chronic carbon monoxide exposure, which include cardiac arrhythmias and neurological damage.

Beyond the carbon monoxide debate, the 2026 Prohibited List introduces critical guardrails for beta-2 agonists, the class of drugs commonly found in asthma inhalers. Salmeterol, a long-acting bronchodilator, has long been permitted for athletes with asthma, provided they do not exceed a maximum delivered dose of 200 micrograms over a 24-hour period.[1]

However, sports physiologists have noted that taking a massive dose of salmeterol all at once can cross the line from therapeutic airway dilation to an ergogenic, or performance-enhancing, effect. High acute doses of beta-2 agonists can act as central nervous system stimulants and, over time, exhibit mild anabolic properties that aid in muscle retention.[2]

To eliminate this loophole, regulators have instituted a strict new dosing interval. While the 24-hour maximum remains 200 micrograms, athletes are now forbidden from inhaling more than 100 micrograms in any eight-hour window. This ensures the medication is used steadily for its intended therapeutic purpose rather than being weaponized as a pre-race stimulant.[1][2]

The 2026 update also peers into the microscopic future of cheating, explicitly banning the manipulation of cellular components. Previous iterations of the anti-doping code prohibited gene doping and the transfer of whole cells, but scientists warned that the next frontier might involve injecting isolated organelles.[2]

Specifically, the new rules ban the transfer of mitochondria and ribosomes. Mitochondria are the powerhouses of the cell, responsible for generating the adenosine triphosphate that fuels muscle contractions. By theoretically injecting highly efficient, lab-cultured mitochondria directly into muscle tissue, an athlete could drastically boost their aerobic capacity without triggering traditional whole-cell doping tests.[1]

In the realm of traditional pharmacology, the agency has also tightened the language surrounding anabolic agents. The 2026 list clarifies that all esters of prohibited anabolic steroids are explicitly banned. An ester is a chemical modification attached to a drug molecule that dictates its half-life, determining whether the substance releases slowly over weeks or rapidly over days.[2]

By explicitly naming esters, regulators are preventing athletes and rogue chemists from arguing that a modified, long-acting version of a banned steroid is technically a different, unlisted compound. The list also adds pegmolesatide as a named example of a prohibited EPO-mimetic, further crowding out the gray areas in peptide hormone regulation.[1][2]

Enforcing these new rules, particularly the carbon monoxide ban, will present a significant logistical challenge for anti-doping authorities. Because carbon monoxide clears from the human body relatively quickly, detecting repeated, non-diagnostic use through standard blood or urine testing is notoriously difficult.

Instead, enforcement will likely rely heavily on the biological passport system, which tracks long-term fluctuations in an athlete's blood profile, alongside intelligence-gathering and whistleblowers. If an athlete's red blood cell count spikes inexplicably without a corresponding high-altitude training block, investigators will now have the regulatory framework to pursue carbon monoxide misuse as a formal doping violation.