Chris Froome turned down the use of a therapeutic use exemption during the second of his three Tour de France wins, the Briton has revealed.
The Team Sky rider, who has admitted to receiving TUEs twice during his career, rejected medical help during the last week of his 2015 success.
He a second yellow jersey by one minute and 12 seconds from Colombian rival Nairo Quintana, who finished the stronger of the two on the climb of Alpe d'Huez in the penultimate stage.
Froome has revealed he was struggling with an unspecified ailment but did not accept any assistance.
"I didn't feel having a TUE in the last week of the Tour was something I was prepared to do," he told the BBC. "It did not sit well morally with me."
Cycling's use of TUEs -- banned drugs are allowed to be used to treat medical conditions -- came under scrutiny after Russian hackers Fancy Bears published confidential details of athletes' TUEs.
Froome's two TUEs were both for a week's oral course of the anti-inflammatory drug prednisolone to treat chest infections that aggravated his asthma in 2013 and 2014.
Former Team Sky teammate Sir Bradley Wiggins, who also suffers from asthma and in 2012 became Britain's first Tour de France winner, had three TUEs for anti-inflammatory drug triamcinolone, taken on the eve of the 2011 and 2012 Tours de France and 2013 Giro d'Italia.
There was no suggestion that either Froome, Wiggins or Team Sky had broken any rules.
Froome has in the past spoken about his belief the TUE system in cycling is "open to abuse".
And he reiterated his desire for the World Anti-Doping Agency to clamp down on their use.
"The fact that we're having that debate about authenticity means there's a problem with the system," he said.
"I think WADA need to tighten their regulations around TUEs, so they're not something that we question, their legitimacy.
"It's not good for sport in general. The fact that we're discussing the validity of results, that brings it back to the authorities, it is something they need to tighten up on so that there aren't questions being asked anymore."