Iga Świątek, a tainted melatonin, and what Informed Sport really stops

On 28 November 2024 the International Tennis Integrity Agency gave Iga Świątek a one-month ban. She had been the world No. 1 in August 2024, when the sample was taken. The substance found was trimetazidine (TMZ). It is a Hormone and Metabolic Modulator on the WADA Prohibited List. It sits in category S4, more exactly S4.4. It is banned in and out of play.

The ITIA found and accepted the source. It was a regulated melatonin medicine, sold without a script and made in Poland. That is the odd part. It was a plain pharmacy product, not a sports supplement. The taint was not in a pre-workout. It was in a sleep aid that many non-athletes take and trust.

Strict liability is what does the damage

Under the WADA Code, an athlete owns any banned substance in their body. It does not matter how it got in. Świątek met the ITIA test for “No Significant Fault or Negligence”. Her fault was set at the lowest end. That cuts the ban, but does not erase it. The first ban ran from 12 September to 4 October 2024. It cost her three Asian-swing events: the Korea Open, the China Open, and the Wuhan Open. She lost the ranking points and prize money, and paid to find and test the source.

This is not a one-off

Other athletes clear their names the hard way. They find and test the source in a lab, at high cost. Two recent tennis cases show this.

• Simona Halep (2022). She tested positive for roxadustat at the 2022 US Open. A tribunal first banned her for four years in September 2023. CAS cut that to nine months on appeal in March 2024. The panel agreed the source was a tainted collagen supplement.
• Jannik Sinner (2024). He tested positive twice for clostebol in March 2024. The source was Trofodermin, a clostebol skin spray sold over the counter in Italy. His physio used it on a cut finger, then handled Sinner without gloves. A tribunal first cleared him in August 2024 (“no fault or negligence”). WADA appealed. The case settled on 15 February 2025 with a three-month ban under a case-resolution deal. He served it from 9 February to 4 May 2025.

Sinner’s source was a cream, not a supplement. But the strict-liability rule is the same.

What Informed Sport actually does about this

Informed Sport is a UK-run scheme run by LGC. It tests every batch of a certified product against the WADA Prohibited List. The tests run in an ISO/IEC 17025-accredited lab. That makes it a real taint check, not just a factory audit. The site check also targets shared production lines. A clean ingredient can pick up banned traces from kit used before. Informed Sport is the every-batch tier of the LGC scheme. Informed Choice is sample-based.

The honest caveat

Informed Sport does not certify pharmacy products. So it would not have caught the melatonin in Świątek’s case. This is not a story about it stopping that taint. It shows how strict liability works, and how harsh it can be. But athletes do have a choice in some categories: protein, pre-workouts, electrolytes, BCAAs, and recovery products. There, batch-tested certification is the only check you can run up front. The chance of a taint is low. The cost to a career is huge. That makes the choice easy.

Practical takeaway

For a tested UK athlete, the rule is plain. In covered categories, take only Informed Sport-certified products. Check the lot code at sport.wetestyoutrust.com. The exact lot on the bottle must match a result in the database. A brand in the list without the matching lot is not enough. The check applies to a batch, not the brand. UKAD’s own “Managing Supplement Risks” guidance says the same: use only batch-tested products, and check the batch number first. UKAD backs no one product. But Informed Sport is the batch-tested scheme it points to. It will not remove every risk, as Świątek’s case shows. But where you have a choice, it is the best one.

You can browse all Informed Sport products on Certwell, or read the longer reference on how Informed Sport testing works.