Detectives are investigating how bottles of painkilling morphine on a hospital ward were diluted with water, it has been disclosed.
Police were called in after it was suspected that liquid morphine on a surgical ward at the Royal Sussex County Hospital in Brighton, East Sussex, had been tampered with.
No arrests have been made and the trust which runs the hospital said no patients have been harmed and no further incidents have been reported.
Stricter controls on the storage and dispensing of the drug have been introduced across the hospital following the alert, Brighton and Sussex University Hospitals Trust said.
Trust chief executive Duncan Selbie said: “Over the weekend of March 3 and 4, we discovered that on one of our surgical wards at the Royal Sussex County Hospital, a small number of bottles of liquid oral morphine appeared to have been watered down.
“We immediately introduced stricter controls on the storage and administration of oral morphine and the incident has been reported to the police.
“There has been no harm to patients and no further incidents but this is nevertheless a serious matter and until we fully understand the nature and cause, these stricter controls will remain in place across the hospital.”