The incident, which happened in the town of Weiden in Bavaria, saw a 52-year-old man die. Eight others aged between 33 and 52 were left in a critical condition, police told German news agency DPA.
Senior prosecutor Gerd Schaefer confirmed that the toxicology tests showed the poisonous substance found in the drink was known but he would not confirm media reports that said it was Ecstacy.
The incident reportedly happened after a group of people had ordered a bottle of champagne and shared it between themselves.
After police arrived at the scene, they found people lying on the floor with cramps, resulting in eight being taken to hospital.
Mr Schaefer said negligent homicide is suspected but he would not give further details, reported Evening Standard.
Similarly last year, German police launched a murder investigation after six people were hospitalised in a case of suspected poisoning at Darmstadt Technical University.
They had all had food or drink from a small kitchen on the university’s Lichtwiese campus.
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The cases sparked many club-goers to boycott certain venues across the UK over fears for women’s safety.
Huge crowds took to the streets to protest the ‘spiking epidemic’, with demonstrations held in more than 40 university towns and cities.
In a report published last month into the spiking inquiry, Harwin said none of the cases of reported needle spiking had yet resulted in a prosecution, and police recognised that was “not enough”.
He said forces had to do more to stop offenders, make them realise they are committing a serious offence and change their behaviour.