A cake given to nurses by a grateful relative of a hospital patient turned out to have been laced with cannabis.
It was presented as a thank-you gift - but nobody recognised the "strange odour" of the Class B drug until a member of staff had eaten a slice.
The man who gave staff the cake - left over from a birthday party for his grandson - did not realise its contents, police said.
Warrington Hospital said the staff member who tucked in was unaffected.
'Strong words of advice'
Cheshire Police said officers had been made aware that a homemade cake "suspected to contain drugs" had been given to staff at the hospital on 27 May.
Tests later showed the cake - reported to be a red velvet cake - did indeed contain cannabis.
"Following an investigation, officers determined that the member of the public who had brought in the cake was unaware of the content of the cake as it had been left over from their grandson's birthday party," said a spokesman for the force.
Police said no action had been taken, but the man's grandson received "strong words of advice" and the cake was destroyed.
Warrington and Halton Hospitals NHS Foundation Trust said it had interviewed all staff, and patient care had not been put at risk.
Chief nurse Kimberley Salmon-Jamieson said one nurse ate a small piece of cake before leaving at the end of their shift.
"We are now working with staff to exercise caution on receiving edible gifts," she added.