Six people have been kept in hospital overnight after taking a “bad batch” of drugs, police said.
The psychoactive substances, including Spice, Killer Smeg and SpongeBob, are thought to have been bought in the Old Eldon Square area of Newcastle.
The drugs previously fell under the category of so-called “legal highs” before being banned in May.
Police said the six people suffered an adverse reaction but are not thought to be in a life-threatening condition.
Northumbria Police has urged anyone in possession of the drugs to hand them in to police to avoid anyone coming to further harm.
Ch Insp 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.
“If you have drugs of this nature in your possession, or have any information about who may be distributing them, then contact police immediately.”