Five-time Grand Slam champion Iga Swiatek accepted a one-month suspension after testing positive for the banned substance trimetazidine, a heart medication known as TMZ, the International Tennis Integrity Agency announced Thursday.

Swiatek failed an out-of-competition drug test in August, and the ITIA accepted her explanation that the result was unintentional and caused by the contamination of a nonprescription medication, melatonin, that Swiatek was taking for issues with jet lag and sleeping.

It was determined her level of fault was “at the lowest end of the range for no significant fault or negligence,” the ITIA said.

“This experience, the most difficult in my life so far, taught me a lot,” Swiatek, a 23-year-old from Poland, said in a video she posted on social media.

“The whole thing will definitely stay with me for the rest of my life. It took a lot to return to training after the situation nearly broke my heart, so there were many tears and lots of sleepless nights,” Swiatek said, speaking in Polish with an English translation scrolling across the top of the post. “The worst part of it was the uncertainty. I didn’t know what was going to happen with my career, how things would end or if I would be allowed to play tennis at all.”

This is the second recent high-profile doping case in tennis: The top-ranked man, Jannik Sinner, failed two tests for a steroid in March and was cleared in August, right before the start of the U.S. Open, which he went on to win for his second Grand Slam title of the season. Sinner did not miss any competition; the World Anti-Doping Agency has appealed the ruling that exonerated him.

Swiatek reached No. 1 in the WTA rankings for the first time in April 2022, and she remained there much of the time since but is now at No. 2 after being overtaken by Aryna Sabalenka in October.

Swiatek won the French Open in June for her fourth title there and fifth major championship overall, then took home a bronze medal at the Paris Olympics in early August.

“The WTA fully supports Iga during this difficult time. 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 women’s tennis tour said in a statement. “The WTA remains steadfast in our support for a clean sport and the rigorous processes that protect the integrity of competition. We also emphasize that athletes must take every precaution to verify the safety and compliance of all products they use, as even unintentional exposure to prohibited substances can have significant consequences.”

Swiatek formally admitted the anti-doping rule violation on Wednesday and accepted her penalty. TMZ is the drug at the center of the case involving 23 Chinese swimmers who remained eligible despite testing positive for performance enhancers in 2021.

Swiatek said she was “shocked” by her test result and had never heard of TMZ. She said she’s been using melatonin “for a long time,” adding that “all my traveling, jet lag and work-related stress mean that sometimes without it, I couldn’t fall asleep.”

She already was provisionally suspended from Sept. 22 to Oct. 4, missing three tournaments during the post-U.S. Open hard-court swing in Asia — the Korea Open, the China Open and the Wuhan Open.

That provisional ban was ended after her appeal showed that her test result came inadvertently from contaminated melatonin.

Because the ultimate agreement was for a month suspension, she will serve the remaining eight days now, while there’s no competition, and be cleared to return to play as of Dec. 4.

“I can start my new season with a clean slate, focused on what I’ve always done — simply playing tennis,” said Swiatek, who hired Wim Fissette as her coach in October.

Swiatek also was fined the prize money of $158,944 that she earned for her semifinal run at the Cincinnati Open in August, the event immediately following the positive test.

“Once the source of the TMZ had been established, it became clear that this was a highly unusual instance of a contaminated product, which in Poland is a regulated medicine. However, the product does not have the same designation globally, and the fact that a product is a regulated medication in one country cannot of itself be sufficient to avoid any level of fault,” ITIA CEO Karen Moorhouse said.

“Taking into account the nature of the medication, and all the circumstances, it does place that fault at the lowest end of the scale,” Moorhouse said. “This case is an important reminder for tennis players of the strict liability nature of the World Anti-Doping Code and the importance of players carefully considering the use of supplements and medications.”