Revellers in York have been warned against taking "legal high" drugs after a rise in the number of people being treated in hospital having taken them.
Mephedrone, commonly known as "bubble", "drone", is imported mainly from China and sold legally on the internet as plant fertiliser.
Police said there had been an increase in users having to be resuscitated in hospital.
Anyone who is offered the drug is being urged to contact police.
Police have warned its use can result in severe nose bleeds, nose burns, hallucinations, blood circulation problems, rashes, anxiety and paranoia, fits and delusions.
It has recently been made illegal in a number of countries due to growing evidence of harm.
A North Yorkshire Police spokesman said: "We are having a high incidence of people being brought to A&E via ambulance who are suffering from the effects of this drug to the extent that they are unaware of their surroundings, their actions and it causing people's heart to stop and them having to be resuscitated."