Japanese tennis player handed 10-month ban after testing positive for prohibited substance

The International Tennis Integrity Agency ( ITIA) announced on Thursday that Japanese tennis player Kaili Demi Teso has been suspended for 10 months following a breach of the Tennis Anti-Doping Programme (TADP).

The 19-year old player tested positive for the prohibited substance methylephedrine, a stimulant which was listed on a bottle of over-the-counter cough medicine. However, no independent tribunal issued a ruling of No Significant Fault or Negligence on Teso's part.

Teso reached a career-high world singles ranking of 1243 in June 2025. She provided an in-competition sample while competing in an ITF World Tennis Tour event in Mysuru, India, in October 2024.

The sample was split into A and B samples and the subsequent analysis found both samples contained the substance, which is prohibited under the TADP, in the category of Stimulants. However, Specified Substances do not require a mandatory provisional suspension, therefore Teso continued to compete while a full investigation took place.

Teso admits to ingesting cough medicine

After several interviews with the ITIA, it was concluded that the positive sample resulted from Teso's consumption of the Japanese cough medicine Shin Lulu A Gold s.

Teso's mother and manager admitted to acquiring the cough medicine on her daughter's behalf. Despite representing Japan, Teso's first language is English and thus she was unable to read the ingredients on the label, which listed methylephedrine in Japanese script.

Although the ITIA accepted that the violation was not intentional, it was also noted by the independent tribunal that the player had received recent education on anti-doping and the risk associated with over-the-counter medications. Therefore, given the medication was purchased in advance of the event, there were a number of additional steps the player could have taken to reduce the risk.

Subsequently, any results, prize money and ranking points from the event in which the player tested positive are forfeited. Teso's period of ineligibility is effective from the date of the written decision, August 7 2025, and will end on June 6 2026.

During the period of ineligibility, Teso is prohibited from playing in, coaching at, or attending any tennis event authorized or sanctioned by the members of the ITIA (ATP, ITF, WTA, Tennis Australia, Fédération Française de Tennis, Wimbledon and USTA) or any national association.