An Ottawa man has been charged after five people took a drug sold as crack cocaine in downtown Ottawa Wednesday night and suffered what police describe as "serious medical complications."

The five people were initially found under the influence of the tainted drug at around 8 p.m. near George St.

"There was vomiting, shortness of breath, difficulty breathing, turning blue, losing consciousness," said acting Staff Sgt. Ian McDonell.

All five received treatment for non-life threatening injuries. A sixth person with similar symptoms was found shortly afterward, although police later deemed the case unrelated to the other five.

The medical complications were caused by unidentified chemicals that had apparently been added to the drug, police said.

Police have charged an Ottawa man after five people were sickened by tainted drugs in the ByWard Market area. (CBC)

McDonell said that police officers just so happened to be in the ByWard Market area conducting a "proactive investigation" at the time and subsequently arrested one person.

The 29-year-old man is facing two counts of possession of a controlled substance, one count of trafficking, one count of possession of the proceeds of crime under $5,000, and two counts of breaching probation.

The man's name has not been released to protect the investigation, police said.

Tainted drugs not uncommon, police say

Street drugs are often mixed with substances that can harm the person who's purchased them, McDonell said.

"It's never good to begin [with]," he said. "What you're getting, there's probably a good chance it's not what you're being sold, what you're told you're being sold."

The drug has since been sent to Health Canada for further analysis. Police are urging anyone believing themselves to be at risk from the drug to call 911 immediately.