Two people have died and a third is in a coma after a doctor at a group therapy session gave participants drugs, Berlin police said today.

Local media reported the participants were taking part in a group psychotherapy session in Berlin's Hermsdorf district on Saturday, when they began to feel nausea and vomit.

When police arrived at the house they found the body of a 59-year-old man. A 28-year-old died later in hospital, a BBC correspondent in Berlin said.

"At this session the participants were given substances. What kind of substances these are... has to be investigated now,” police spokesman Michael Gassen told the BBC:

Gassen said the doctor admitted handing out the drugs in order to "expand the patients' consciousness" and to offer "help with spiritual crises." Some local reports suggest heroin, amphetamines and ecstasy were used. It is not known how the drugs were administered.

The 50-year-old doctor has been arrested and questioned by detectives, Gassen said. It is believed his wife was one of the participants in the course.

Nine of the participants have since been released from the hospital. One patient was still in critical condition in a coma.

Click here for more on this story from news.com.au.