Olympic swimming medallist Ben Proud has become the first British athlete to join the Enhanced Games, an event which allows athletes to take performance-enhancing drugs.
The 30-year-old, who won silver in the 50-metres freestyle in Paris last summer, does not believe the event undermines clean sport.
"I think [the Enhanced Games] opens up the potential avenue to excel in a very different way," he told BBC Sport.
"I think realistically I've achieved everything I can, and now the Enhanced is giving me a new opportunity. I definitely don't think that's undermining a clean sport.
"I really respect the sport I've been part of, and I would never step back in knowing I've done something which isn't in the rules."
Proud said he had found athletes committing doping violations in the traditional version of his sport "incredibly frustrating."
The Enhanced Games permits athletes to take substances approved by the United States Food and Drug Administration (FDA), under strict supervision.
"I will never take anything that I am unsure of," Proud added. "They are not allowing anyone to participate if they are under any stress or health risks."
The inaugural Enhanced Games are scheduled for May next year in Las Vegas.
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Aquatics GB said in a statement it was "immensely disappointed" by Proud's decision.
"Aquatics GB, along with our partners, stand firmly behind the values and principles of clean sport and condemn Ben's decision in the strongest terms," the statement read.
A spokesperson for elite sport funding body UK Sport said: "UK Sport condemns everything the Enhanced Games stands for in the strongest possible terms.
"We believe it risks compromising athlete health and welfare, undermines the trust of fans and is the absolute antithesis to our philosophy of winning well. We are incredibly disappointed to learn that any British athlete in one of our Olympic or Paralympic programmes would support such an event.
"We are engaging with our colleagues at Aquatics GB as a matter of urgency to determine Ben Proud's suitability to receive public funds.
"It is clear however that any breach of anti-doping rules is contrary to the policies which any athlete must comply with to receive UK Sport funding."