In an update Monday afternoon, Philadelphia police tell Action News one person was transported to Children's Hospital of Philadelphia, three were taken to Hahnemann University Hospital, and one went to Thomas Jefferson University Hospital.
Police believe that at least 2 took the drug ecstasy.
The incident began when the doors opened at 8:30 p.m. Saturday at the Electric Factory.
Zeds Dead, a Canadian electronic music duo, was supposed to take the stage at the Spring Garden venue in front of hundreds of fans who came from all over.
But police, along with the city, shut down the concert when people, some teenagers and others in their early 20s, started collapsing.
Samuel Hoppus and Randall Wilson of Media, two concertgoers, are still holding on to their tickets which cost $40 each.
"We were real excited and we were ready to go; it was awesome and we paid a lot of money for it. It was really disappointing," Hoppus said.
Zeds Dead's Facebook page has been flooded with dozens of comments and complaints about the cancellation.
The show was open to all ages, but Hoppus and Wilson were still surprised to see a large number of concertgoers they believe were under the age of 18.
"Definitely didn't look like it was just 18 and up, and most of the people I seen look like they had a hard time standing up were, definitely, look like they were younger," Wilson said.
For Hoppus and Wilson, they're thankful no one died, but they're hoping for a refund or another chance to see one of their favorite music group.
"Why should I get punished for a couple of people not being able to handle themselves out in public?" Wilson said.
The Electric Factory was not available for comment Sunday night.
On its website, the Electric Factory is asking for visitors to check back or more information on the canceled show.