Police investigating a mass intoxication of a homeopathy conference in Germany with psychedelic drugs have said they still do not know nearly a week later whether it was an accident or an experiment gone wrong.

Emergency services called to the meeting in Handeloh, south of Hamburg, last Friday afternoon found a group of 29 alternative healers hallucinating, staggering around, groaning and rolling on the grass.

Police spokesman Lars Nicklesen said on Thursday that investigators believe a psychedelic drug was to blame but remain unsure of how or why it was taken. The delegates are now all out out of physical danger, he said, but there may yet be legal consequences for the healers in the course of the ongoing criminal investigation.