Sweets that caused thirteen teenagers to become ill were laced with a psychoactive compound found in cannabis, police say.
The confectionery – which the north London school pupils thought were normal treats – was believed to have contained tetrahydrocannabinol, known as THC.
The ambulance service was called shortly before midday to La Sainte Union Catholic School in Highgate, north London.
The youngsters were treated at the scene and taken to hospital as a precaution but the Metropolitan Police said none are believed to be “seriously unwell”.
The force said: “Police were called by London Ambulance Service at around 11.45am on Monday, 5 October, to reports of children feeling unwell having eaten what they believed to be sweets at a school in Highgate Road, NW5.
“As a precaution, 13 children have been taken to hospital. Their parents have been informed. Nobody is believed to be seriously unwell.”
The full circumstances are being investigated, the Met said, but no arrests have been made and the school has not been evacuated.
A spokeswoman for the London Ambulance Service said: “We were called at 11.44am today to reports of an incident at La Sainte Union Catholic School, Highgate.
“We dispatched a number of resources including a clinical team leader, five ambulance crews, medics in cars and incident response officers.
“We treated 13 teenagers at the scene and took them to hospital.”