Six people have been taken to hospital after taking a "bad batch" of so-called legal highs, police said.
Those involved in the incident in Newcastle are thought to have suffered an adverse reaction to new psychoactive substances (NPS), prompting Northumbria Police to issue a warning.
The drugs, including substances called Spice, Killer Smeg and SpongeBob, are thought to have been bought in the Eldron Square area of the city, known as Hippy Green.
None of the six is thought to be in a life-threatening condition, although they were kept in hospital overnight as a precaution.
Anyone with the NPS, formerly known as legal highs, has been urged to hand them in to police to avoid anyone coming to further harm.
Chief Inspector Barrie Joisce said: "So far we have not received any reports of a life-threatening reaction to these drugs but we are concerned that people could be putting themselves at risk.
"Here in Northumbria we have done a lot of work warning people about the dangers of legal highs and they were recently banned under new legislation brought in earlier this year.
"However, our priority is the safety of the public and we want to make sure that any substances that may cause harm to those using them should be taken off the streets.
"If you have drugs of this nature in your possession, or have any information about who may be distributing them, then contact police immediately."
Anyone with any information about the drugs should contact police on 101 quoting reference 1013.