Police say a batch of dangerous medication may have been lost in the Newton or Earlestown areas.
Two blister packs of tramadol hydrochloride containing a total of 36 tablets had been left sometime between 7.30am and midday on Wednesday.
They are believed to have been lost in the Crow Lane area of Newton-le-Willows, around the Bridge Street area of Earlestown or in Mesnes Park, Wigan.
A spokesman for Merseyside Police said: “Officers are reminding people that taking any medication which has not been prescribed for them can be dangerous and, in some circumstances, can prove fatal.
“Anyone who finds any of the medication is asked to hand it in to any pharmacy or police station or call officers on the 101 number.”