BERLIN (AP) — German police are investigating after several women reported feeling unwell following an event hosted by the parliamentary group of Chancellor Olaf Scholz’s party.

Berlin police said Saturday that the investigation was triggered by a 21-year-old woman, who felt dizzy and unwell several hours into Wednesday’s summer party for the Social Democrats and then was unable to remember the evening the following day. She went to a hospital for checks, and police ordered a blood test for analysis of possibly toxic substances.

The woman ate and drank at the event, but didn’t consume any alcohol, police said. By Saturday morning, another four cases in which people reported similar symptoms had emerged. German media reported that they apparently were victims of so-called “knockout drops,” which can be mixed into drinks or food. Police said they were awaiting test results.

Police opened an investigation of persons unknown on suspicion of bodily harm. Both they and the center-left Social Democrats said they weren’t aware of any offenses beyond that.

The Social Democrats’ co-leader, Lars Klingbeil, told Welt television he was “furious that something like this could happen at an event” organized by the party. He said the parliamentary group’s leadership is cooperating with authorities and he hopes “that the perpetrator or perpetrators can be caught and then brought to account.”

About 1,000 people attended the annual party on Wednesday, including the chancellor, party lawmakers, and their employees.