The first doping violation in a domestic Japanese swimming competition has been confirmed, an official source said Sunday.

The swimmer was tested at an intercollegiate competition in Osaka Prefecture in September. The Japan Anti-Doping Agency will decide on a punishment in the coming days following the swimmer's positive result on the "B" sample.

According to a source, the swimmer took supplements produced overseas whose labels did not mention the banned stimulants they contained. Although it is not considered a serious violation, the swimmer is likely to be found to be negligent.

The swimmer in question has participated in national freestyle sprints at the high school level but has not represented Japan in senior international competitions.