New Year’s Eve revelers sickened at a rock concert after some drank an orange-liquid may have been hit by a combination of synthetic drugs, a hospital director said Wednesday.

Dr. Robert Splawn said concert-goers treated at the California Hospital Medical Center displayed a variety of drug reactions. He was unsure what role the orange liquid played in the illness.

“Apparently several drugs were being abused,” Splawn said.

At least 31 people were treated at area hospitals for dizziness, nausea and shortness of breath, and paramedics treated 20 at the Olympic Auditorium where the all-night rock concert was held. Two people remained hospitalized Wednesday for drug overdoses; a third was critically injured when he was struck by a car in the melee that erupted when the concert was stopped.

The concert by the band “In 7th Heaven” ended well before midnight when firefighters found 10,000 people crammed into the auditorium - including four who were unconscious. The departing crowd threw objects, broke windows and at one point attacked a city bus - rocking it back and forth.

Six people were arrested at the concert for investigation of selling and distributing drugs.

Splawn said the sickened revelers didn’t appear to know what was in the drink, which they referred to as “orange rush.” Concert organizer Terry Cowan told reporters that the drink was a legal, herbal stimulant and that 100 bottles were handed out to the crowd.

Police seized as many as 10,000 vials of the liquid. Test results were expected Thursday or Friday.

Drug experts and Los Angeles health officials couldn’t be reached Wednesday because of the New Year’s holiday.