Police say a female employee at the restaurant took hash cakes her daughter had made for a different occasion.
Mourners ended up feeling high and nauseous when they were accidentally served hash cake at an after-funeral gathering in Germany.
Police said that after the burial in Wiethagen the funeral party retired to a restaurant for the German custom of consuming coffee and cake.
But 13 people in the party experienced nausea and dizziness afterwards and needed medical treatment.
Police discovered the restaurant employee in charge of the cakes had asked her 18-year-old daughter to bake them.
The daughter baked the cakes and placed them near hash cake which she had previously prepared for another occasion.
Her mother took the hash cake to the restaurant for the funeral by mistake.
Police said the daughter is now under investigation.
Details of the incident in August have only just been revealed.