Funeral goers met following the ceremony for a traditional cake and coffee reception at an open-air charcoal kiln museum in Wiethagen, near Rostock in the east of the country.
But towards the end of the wake attendees began to complain of a feeling of malaise.
The widow was raced to hospital amid concern she was suffering a stroke, local media reported.
When the other 12 attendees also requested medical treatment, drug tests were carried out and police stepped in to investigate.
It was then revealed the cake, which had been baked by the 18-year-old daughter of an employee at the site, had a secret ingredient.
Officers believe the cake had initially been baked for the teenager’s own use and was stored alongside several she had baked for the wake.
Police spokesman Christopher Hahn said the teenager’s mother “had taken the wrong brownie cake without consulting her”.
He added that some attendees were left with “serious health problems” and a number forced to stay in hospital as a result of the contaminant.
The teenager is now being investigated in relation to 13 cases of negligent and dangerous bodily injury, disrupting a funeral and violation of the Narcotics Act, according to German newspaper Nordkurier.
The Independent
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