Police have issued a warning after two suspected drugs-related deaths in Leeds and Wakefield.
Officers were called to Compton View, Harehills, at around 8.30am on Saturday and found the body of a 36-year-old man inside.
And just four hours later, police were called to Park Green, Normanton, Wakefield, at 12.50pm and found a man, 27, suffering from breathing difficulties before then being pronounced dead.
Police are now warning Class A drug users that their deaths are believed to be drugs-related.
Officers are awaiting toxicology results to confirm the causes.
Four people are in custody today after being arrested in connection with the incident at Compton View.0
Detective Chief Inspector Jim Dunkerley, of West Yorkshire Police, said: "Enquiries remain ongoing into both these men's deaths. While we are awaiting full toxicology results we do believe these deaths are Class A drugs related.
"The force is aware of warnings issued by other forces in the Yorkshire and Humber region about unusually strong heroin or heroin derivates potentially being in circulation, and given that, it seems prudent to issue a warning now to local drugs users.
"There is no information to suggest such drugs are in circulation here in West Yorkshire but, given the unusual circumstances of two suspected Class A drugs deaths in less than 24 hours, we are conducting enquiries.
"Taking Class A drugs is of course, extremely risky in itself, but we would urge users who experience unusual side effects from taking heroin or substitutes to seek medical help via 111 or in life threatening situations 999.
"Anyone who has information about the distribution of illegal Class A drugs in West Yorkshire is asked to contact West Yorkshire Police on 101.
"Information can also be given anonymously to the independent Crimestoppers charity on 0800 555 111."