Serena Williams on '15 exemption: 'I've never tested positive'

Serena: 'I've never tested positive' for banned substances (1:07)

Serena Williams defends herself by saying she has never taken banned drugs throughout her career and she never will. (1:07)

INDIAN WELLS, Calif. -- After her opening-round win Thursday at Indian Wells, Serena Williams was asked about a backdated therapeutic use exemption (TUE) she received at the 2015 French Open.

"I've never tested positive [for an illegal substance]," Williams said. "I've always gotten a TUE, so you should fact check that. I wasn't going to play [the French Open] unless I had a TUE because if you remember that year I was incredibly sick."

Williams missed practice sessions and interviews along the way and needed five three-set wins to claim the title.

"I don't think I have ever been this sick," Williams told reporters at the time. "I can't believe I won because I got the flu after my third-round match and haven't been getting better."

Reports show Serena was granted a TUE for prednisone to help alleviate some of the coughing fits and other symptoms throughout the event.

"I don't know how I even won the [tournament], and I said I literally can't play the final," Williams said Thursday.

Serena also said that in the 20 years she has been on tour, she always has been happy to answer any drug-related questions.

"I take pride in, especially having a daughter and having a kid -- I'm never going to be able to look my kid in the eye and say, 'Mom cheated,' or mom did something like that," Williams said. "That is totally irresponsible and even before that I've always had that attitude."