The public is being warned to be cautious after a quantity of medication was lost.
Merseyside Police believes that the medication was lost on the 10a bus between St Helens town centre and Rainhill this morning, Tuesday.
The medication includes Zapain and Diazepam tablets.
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.