Seven schoolchildren were rushed to hospital after taking a 'legal high' during their lunch break.
The teenagers started to feel faint and sick after returning to classes at Pembroke Comprehensive School in West Wales.
Ambulances and an air ambulance were called to take the pupils to hospital. Police said none of the children were in a life-threatening condition.
Experts are now analysing samples of the legal drug.
A Dyfed-Powys Police spokesperson said: "The ambulance service informed us of an incident they were dealing with at Pembroke Comprehensive School.
"A group of pupils had become unwell. Officers attended the scene and established that a number of pupils were affected.
"Some were treated at the scene and released but others were conveyed to the Accident and Emergency department at Withybush Hospital in Haverfordwest as a precaution.
"None are believed to be in a life threatening condition.
"Early indications are that the group may have reacted to a type of legal high."
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