A woman collapsed in a Rugby nightclub and was taken to hospital after taking an ecstasy tablet in the early hours of Saturday.
The 20-year-old took the tablet - believed to be MDMA (ecstasy) - at a town centre nightclub in Church Street.
Ambulance crews were called to the late-night venue after she suffered an adverse reaction to it at around 4am on Saturday morning.
The woman, who admitted taking the tablet which was purple in colour, said it was sold to her by a man described as smartly dressed and in his late 20s.
She was admitted to hospital and later discharged.
Police in Rugby have now issued a warning after the incident.
Detective Sergeant Alistair Knight said: “Anyone who may have also taken one of these tablets should seek medical attention as soon as possible.
“We would like to remind anyone thinking of taking illegal drugs that you really don’t know what the substances are made of and how they will affect you.
“Police are working hard to find those responsible for bringing class A drugs to Rugby. Anyone with any information should call police on 101.”
Alternatively call Crimestoppers anonymously on 0800 555 111.