Detectives have launched investigations into four drug-related deaths within 48 hours in south Essex.
Essex Police said it was remaining “open-minded” about whether the deaths of three men and one woman on Monday and Tuesday were linked.
All the victims died in neighbouring towns within 10 miles of each other.
On Tuesday a man in his 40s died at an address in Canvey Island and a man in his 20s was found dead in Benfleet.
The previous day, a man in his 20s was found dead in Leigh-on-Sea and a woman in her 30s died in Westcliff-on-Sea, a suburb of Southend.
Detective chief inspector Stephen Jennings said: “At this stage it is not clear if these deaths are linked but we remain open-minded about that possibility and our enquiries are ongoing.
“We believe the deaths are all related to the taking of illicit drugs.
“I would urge people not take any illegal substances at any time but particularly not at this time.”
