Three women have been treated in hospital following suspected injection spikings in Sheffield night clubs, police said.
Two 18-year-old women were discharged but a 19-year-old woman is in a stable condition after being injected over the weekend, South Yorkshire Police said.
A spokesman said inquiries "continue at pace to trace those involved".
Det Ch Insp Benjamin Wood said the injections were "not a joke" and those responsible were "endangering lives".
The first woman, aged 18, was injected at about 02:00 BST on Saturday in a club on Eyre Street.
She became ill and was taken to hospital via ambulance but has since been discharged.
At about 04:00 GMT on Monday, a 19-year-old woman was injected at the same venue.
'Careless and cruel'
She also became ill and was taken to hospital where she remains in a stable condition.
Another 18-year-old woman was injected at a club on Carver Street on Saturday and was taken to hospital, since when she has been discharged.
Det Ch Insp Wood said: "Everyone should be able to enjoy our night-time economy without the fear of being harmed.
"If you have been spiked, it is not your fault in any way and it is nothing you should feel ashamed of. The blame lies solely with those committing this type of crime.
"I'm now addressing those people: if you are responsible for these incidents, it is not a joke. It is not a bit of fun.
"Consider the results of your careless and cruel actions: you are endangering the lives of innocent people who just want to go out and have fun with their friends. You are putting them at risk of serious illness, injury or assault.
"You are committing a serious crime, which could result in you being put behind bars for more than 10 years."