The six were among 27 Elements Music Festival attendees who wound up at the hospital, the Canadian Broadcasting Corp. reported.
"In my three years of doing this job, I have never seen an event with these sorts of numbers," police Sgt. Nicole Chapdelaine told the network.
"Some people have suggested that there's no difference between this event ... and a busy Saturday evening on Whyte Avenue. I am here to tell you there is absolutely no comparison."
City Councilor Kerry Diotte said he attended Friday night's performances and thought everything was going smoothly.
"I've seen worse situations on Whyte Avenue to be honest," he said. "I was quite struck by the fact people were fairly nice.
"It didn't seem like anybody was looking for trouble. If they did, they'd have been thrown out of there. There was very little tolerance for that."
Several festival-goers were charged with drug offenses, police said. The two-day event was expected to draw about 10,000 people.