American swimmer Kensey McMahon banned for four years. GETTY IMAGES.

Distance swimmer Kensey McMahon has received a four-year ban after testing positive for the blood-boosting drug vadadustat last July. The American protested her innocence, but an independent arbitrator found her "unable to establish through concrete evidence that her violation was not intentional".

The United States Anti-Doping Agency (USADA) provisionally suspended McMahon after she returned a positive test at the US national championships in Indianapolis where she finished third behind Katie Ledecky in the 1500m freestyle. USADA agreed to give the two-time collegiate champion time to investigate the source of the banned substance which, until this April, was not even approved for medical use in the United States. Vadadustat is used to treat anaemia in chronic kidney disease in adults.

McMahon swam for the University of Alabama and took 1500m freestyle bronze at the short-course World Championships held in Melbourne in December 2022. She said on her Instagram that, with the support of the US Olympic and Paralympic Committee, she and a law firm "tested every vitamin, supplement, hydration formula, and medication" she consumed in the months before the positive test.

She added, "I submitted to a polygraph test (which I passed) and hair sample analysis, which was negative (as were all my random USADA doping control tests both before and after July 1st, including one just four days before the positive). The time, energy, effort and expenses poured into figuring out how this happened and trying to prove that this was unintentional has been extensive and exhausting."

USADA and McMahon presented their cases and witnesses on 2 May. With a prohibited substance such as vadadustat, the 24-year-old had to prove - according to USADA - "by a balance of probability, that her anti-doping rule violation was not intentional". As she was unable to find the source, she admitted, "While the arbitrator did not conclude that I intended to cheat, I could not meet my burden of proof under the rules as they are currently written."

Swimming has been under the spotlight of late with Ledecky saying confidence in the Olympic anti-doping system was at an "all-time low". That followed the revelation that 23 Chinese swimmers escaped sanction despite testing positive for trimetazidine in the lead-up to the delayed Tokyo 2020 Olympic Games. Bahamian swimmer Joanna Evans also received a four-year suspension, claiming that her career had been "destroyed by the World Anti-Doping Agency's legal team".

McMahon concluded, "There's been a lot of news and opinions circulating recently regarding anti-doping cases. With each new story, there is more evidence of flaws in the current system and its associated policies and politics. Athletes, like me, are not protected and the system weighs heavily against us. We're presumed guilty and immediately banned from all sports with little recourse.

"I've offered my experience to both USA Swimming and USADA to advocate for change in testing and policy so other athletes and their families might be spared some of the mental and financial stress we have experienced. If this can happen to me, it can absolutely happen to others. I lost the opportunity to see what I was capable of and how far I could go in my sport, and in my pursuit of being a Paris Olympian because of an 'estimate' equivalent of a sprinkle from a saltshaker into an Olympic sized pool."