Two people are in a critical condition in hospital after suspected MDMA overdoses at a music festival.
A 19-year-old woman and a man aged 22 are thought to have taken the drug, also known as ecstasy, at the Reminisce Festival in St Helens, Merseyside.
Police said a number of other people at the one-day festival had also been taken to hospital.
Earlier, event organisers tweeted a warning to festival-goers about “some ‘bad’ blue diamond pills”.
Det Insp Paul Grounds, of Merseyside Police, said: “I want to reassure those affected that we are doing everything possible to identify exactly what substance or substances have resulted in these severe reactions, working alongside the health service.
“We initially believe that ecstasy tablets were taken by some of those in hospital but this is all subject to further enquiries.
“I would urge anyone else who has had an adverse reaction to any substance make themselves known to medical services as soon as possible.
“Likewise, if you are still in possession of any drugs from the event, please do not take them under any circumstances but let us know and we will recover them for further enquiries to be made.”