Fentanyl is a painkiller doctors usually prescribe in patch form.

The drug is 100 times more potent than morphine and is 750 times stronger than codeine, according to Dr. Michelle Arnot, a professor of pharmacology at the University of Toronto.

Fentanyl was originally developed as an anaesthetic used during surgery. But at about the turn of the millennium, it was made into a small patch — the size of a Band-Aid — to be applied to the skin. That allowed the medication to be released transdermally over time. It's normally prescribed to those with cancer pain and severe chronic pain.

On the street, opiate users are extracting the drug, heating it to make it more potent, and injecting it directly into their veins. It offers a quick high and then a quick low.

Users scrape the drug off the patch or cut the patch into pieces. They then either smoke or inject the drug. Some users have been known to suck the patch under their tongues.

Fentanyl's popularity has risen as the availability of opiates such as OxyContin and oxycodone has declined. Ontario delisted OxyContin in early 2012.

On the street Fentanyl is also cheaper than heroin. In 2011, Raffi Balian, co-ordinator of the Counterfit Harm Reduction program in Toronto's east end, said patches were selling on the street for $60. In 2012, Sarnia Police reported patches selling for anywhere between $150 and $400.

Sarnia Police say because the drug is usually linked back to a legitimate prescription, it's tough to get the drug off the street and users off the drug.