The patients, ranging in age from 24 to 56, were hospitalized with symptoms including hallucinations, delusions, breathing problems, high heart rates and cramps.
Investigators said blood and urine tests determined the affected conference-goers had ingested hallucinogenic drug 2C-E, an amphetamine known as Aquarust that has been illegal in Germany since the end of 2014.
Police said they are investigating the incident as a violation of the country's Narcotics Act and they are working to determine whether the convention participants ingested the drug knowingly.
"It must have been a multiple overdose. That does not support the view that the people concerned took the hallucinogen knowingly," Torsten Passie, a member of the German government's narcotics commission, told broadcaster NDR. "One has to assume that people were not told about the substance, its effects and risks before taking it."
Police said none of those suffering from the drug's effects had recovered sufficiently to be interviewed before Monday.
The Association of German Healing Practitioners, which represents homeopathy practitioners, released a statement saying none of its representatives were among those who ingested the hallucinogen at the conference.
"The organizers of this obscure conference are unknown to us and such events will not be tolerated by our association," The Independent quoted a representative as saying. "Unfortunately, the conference in Handeloh has severely damaged the image of the homeopathy profession...and we have clarified that such acts are not in the spirit of natural therapy, and contradict our values both morally and legally."
"The Association of German Healing Practitioners detests such misdemeanors," the representative said.
