World No. 2 and five-time Grand Slam champion Iga Swiatek has accepted a one-month suspension after testing positive for the banned substance trimetazidine (TMZ), the International Tennis Integrity Agency said on Thursday.

Swiatek tested positive in an out-of-competition sample in August, but the ITIA, which runs tennis’ anti-doping program, accepted that it was caused by contamination of her medication melatonin, which was manufactured and sold over the counter in her native Poland.

Swiatek said she had been taking it for jet lag and sleep issues and as there was no significant fault or negligence, the ITIA ruled it was “the lowest end of the range” and offered the reigning French Open champion a one-month suspension that the 23-year-old accepted.

“The player was provisionally suspended from Sept. 12 until Oct. 4, missing three tournaments, which counts towards the sanction, leaving eight days remaining,” the ITIA said in a statement.”

She also forfeited prize money from the Cincinnati Open, the tournament directly following the test.

Swiatek, who had pulled out of tournaments in Asia in September citing personal matters and fatigue, described the ordeal of testing positive as the “worst experience of my life.”

She was world No. 1 when she failed the test and having skipped the Asian swing, Aryna Sabalenka leapfrogged her in the world rankings to eventually end the year in the top spot.

“In the last 2.5 months I was subject to strict ITIA proceedings, which confirmed my innocence,” Swiatek said on Instagram. “The only positive doping test in my career, showing unbelievably low level of a banned substance I’ve never heard about before, put everything I’ve worked so hard for my entire life into question.

“Both me and my team had to deal with tremendous stress and anxiety. Now everything has been carefully explained, and with a clean slate I can go back to what I love most.”

Swiatek, whose anti-doping violation was not made public at the time, had her provisional suspension lifted after providing samples of her melatonin product to the SMRTL laboratory in Salt Lake City, Utah, which is accredited by the World Anti-Doping Agency, which confirmed detecting low doses of TMZ in both opened and sealed containers of the product.

The provisional suspension was lifted on Oct. 4 and the case was forwarded to an independent tribunal.

Swiatek is not the first world No. 1 to fail a doping test this year. Italy’s Jannik Sinner, the men’s top-ranked player, tested positive for anabolic agent clostebol.

Sinner, however, was cleared of wrongdoing by an independent tribunal ahead of the U.S. Open, which he went on to win. The World Anti-Doping Agency has appealed to the Court of Arbitration for Sport (CAS) against the tribunal’s finding of “no fault or negligence.”

With two of the biggest names in tennis escaping lengthy bans for anti-doping violations, questions are being raised about the sport’s reputation.

“These are not cases of intentional doping,” ITIA chief executive Karen Moorhouse said Thursday. “We’re dealing with inadvertent breaches of the rules.

“So I don’t think this is a cause for concern for tennis fans. I think the fact that we’re being clearly open, transparent, and it shows the breadth and depth of our anti-doping program.”

Swiatek played in Cincinnati, where she was the top seed and reached the semifinals. The Women’s Tennis Association (WTA) said she won nearly $159,000 in prize money at the tournament.

Swiatek then took part in the U.S. Open, where she was knocked out in the quarterfinals, before the WTA Finals in Riyadh, where she failed to advance from the group stage.

She also represented Poland at the Billie Jean King Cup, where it lost in the semifinals to eventual champion Italy.

The WTA said it acknowledged the ITIA’s decision and that it fully supports Swiatek.

“Iga has consistently demonstrated a strong commitment to fair play and upholding the principles of clean sport, and this unfortunate incident highlights the challenges athletes face in navigating the use of medications and supplements,” the WTA said.

Russian figure skater Kamila Valieva also tested positive for TMZ, with the result revealed during the 2022 Winter Olympics. She was disqualified from the team competition at the Beijing Games and received a four-year doping ban.