Several pupils have collapsed after vaping 'Spice' mis-sold as 'natural cannabis'.
At least eight children were treated by medics after inhaling what they thought was THC vape liquid, prompting health advisors to issue a new warning in Greater Manchester.
This month an ambulance was called to treat several pupils who'd 'vaped' at a school in Oldham, the Manchester Evening News reports.
Also this month another youngster suffered a seizure at a school in the same town.
And last month a young person collapsed after being forced to vape in Rochdale.
Ambulance crews were called to another school in Oldham after several young people collapsed.
A similar incident unfolded at an educational facility in Bury where a group of pupils became 'heavily intoxicated'.
Three more pupils at a school in Bury required an ambulance for the same reason.
Greater Manchester Police are investigating.
It comes after nine young people collapsed between February and June this year.
The latest warning was issued on behalf of the Greater Manchester Drug Alerts Panel, which brings together police, NHS, local authorities and drug user support agencies.
THC is the chemical that causes the 'high' in cannabis.
In these cases, it was mis-sold as 'THC vape', THC vape pens, THC oil or cannabis oil.
Laboratory testing showed that some of the vials contained the same chemical used to make Spice, while other vials contained no psychoactive substance at all.
Michael Linnell, a drugs use expert who coordinates the multi-agency Greater Manchester Drug Alerts Panel, said: "Young people have bought something that is sold as a ‘natural’ cannabis product but which in fact contains the chemicals found in ‘spice’.
"They think they are getting a product that is highly desirable in their eyes for a bargain price, but they are not.
"They are getting ripped off and they are taking a much bigger risk. Some of the vape bottles contain spice, while others contain no psychoactive substance at all. They can’t know what they are inhaling.
"If they inhale spice they risk the very bad reaction we have now seen on at least a dozen occasions since February involving at least 17 young people.
"The effects of the drug for someone not used to taking spice are very dangerous, unpredictable, and may even be fatal."
Three boys were arrested on suspicion of possession or supply of a controlled substance on Friday, December 6.
Police searched their homes and found illegal vaping products.
Searches were also conducted at schools in Rochdale where similar products were seized.
Greater Manchester Police’s Chief Superintendent Paul Savill of Local Policing and Criminal Justice said: "The offenders undertook a voluntary interview, allowing us to gather further intelligence on the supply of the illegal vaping products as well as educate those involved on the dangers the products pose.
"The three boys have now been released under investigation.
"Suppliers of illegal and dangerous vaping products are recklessly targeting children and the vulnerable and we need the public’s help to identify these suppliers and bring them to justice.
"Alongside safeguarding work we are working closely with schools, partners and stakeholders to reach out to children and with the help of the community, we can remove these products from our streets."
Anyone with information on the sale of illegal vaping products or the sale of other illegal drugs should call police on 101 or the independent charity Crimestoppers, anonymously, on 0800 555 111.