A Manchester school pupil fell ill after allegedly buying MDMA from a 16-year-old schoolboy.
The girl, a year eight pupil at an unnamed South Manchester school, became ill on 25 February but did not suffer any serious or lasting ill-effects. Police believed the drug purchased was a tablet, most likely MDMA.
A 16-year-old boy has been arrested on suspicion of drugs offences and bailed pending further enquiries.
While no other reports have been made to police, local officers believe other school-aged children may be susceptible to similar approaches.
Inspector Luke Breakspear, from the Wythenshawe Neighbourhood Policing Team, said: "We are working very closely with schools in the area – and in turn local parents and pupils – to make them aware of this incident, which we believe could be part of a wider problem.
"We believe MDMA tablets are changing hands for relatively small amounts of cash and some of these are finding their way into the hands of young teenage children.
"We don't know how they are being marketed or sold, so the children may not even be aware exactly what they are buying, but by taking these they are undoubtedly risking their health.
"I want to reassure parents that we are determined to identify those responsible and bring them to justice. If anyone has any information that may help us I would encourage them to get in touch.
"Additionally, I think it is really important for parents to sit down with their children and have some frank discussions about the dangers of drugs."
Anyone with information is asked to call police on 0161 856 4882 or Crimestoppers, anonymously, on 0800 555 111.