An elementary school student in B.C.'s Okanagan Valley has recovered and returned to school after accidentally overdosing on a powerful drug he found on the floor of his classroom.

The eight-year-old swallowed the drug after finding the pinkish, powdery substance at his school in Kelowna last week, the Central Okanagan School District said Monday.

The district said tests of the sample obtained by RCMP show the drug was an illicit form of benzodiazepine — a class of drug commonly prescribed for insomnia, anxiety, muscle spasms and other ailments.

The Central Okanagan superintendent of schools, Kevin Kaardal, said staff thoroughly cleaned the classroom and the space has been inspected by the district's health and safety officials.

A statement said Mounties have not determined how or why the drug was left in the classroom.

"That's our big question and our initial investigation has not determined any simple answers," said Kaardal.

"Was it in somebody's bag? Fell out an adult bag as they dropped their child off at school? Was it somebody from outside the school community? None of those answers seem to be forthcoming."

The school principal spoke to the eight-year-old's class on Monday to help students understand what happened and remind them about the dangers of handling unknown substances.

The investigation is ongoing.