The painkiller fentanyl is being increasingly used on the streets, warn experts, who say the drug is cheaper and 100 times more potent than morphine.

The drug, which has started to show up on the streets of Toronto and other North American cities is 750 times stronger than codeine, according to Dr. Michelle Arnot, a professor of pharmacology at the University of Toronto.

There have been at least three deaths this year and dozens of overdoses due to fentanyl.

Officials with Toronto Public Health are warning street drug users about fentanyl, says Shaun Hopkins, manager of the city's needle exchange program.

"There is a potential for overdose from using fentanyl," says Hopkins, whose program works with more than 10,000 drug users in Toronto. "We're hearing concerns from our clients and we want to prevent any harm associated with using fentanyl."

Small patch for chronic pain

Fentanyl was originally developed as an anesthetic used during surgery. But about a decade ago, 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.

But on the street, opiate users are extracting the drug, heating it, which makes it more potent, and injecting it directly into their veins. It offers a quick high and then a quick low.

"I think a lot of people think, 'Oh, I've got some opioid in a patch here, I can extract it out and get a great high,' but they are not taking into account that it is much more potent, you have no idea of the dose that you've actually taken," says Arnot.

"As I tell my students, something that is very fast on, fast off is more rapidly or more readily abused than something that has a very slow onset and offset. Therefore, that euphoria that is associated with misuse occurs quite rapidly."

At the Counterfit Harm Reduction program in Toronto's east end, co-ordinator Raffi Balian has been educating local drug users about fentanyl, its dangers and how to use it safely.

'Very easy to overdose'

"It's very easy to overdose on fentanyl if you are a novice user," says Balian.

He says fentanyl's popularity has risen as the availability of opiates such as OxyContin and oxycodone has declined. Doctors are writing fewer prescriptions for those drugs because of concerns about abuse and addictions.

Balian says fentanyl is also cheaper than heroin. A 100 mcg (microgram) patch of fentanyl costs between $60 and $75 on the street and, if used appropriately, offers about five times the punch of heroin.

"It's clean, you know what you're getting," Balian says. "And it's cheaper. Cheaper than using heroin."

Balian has already published several articles in local newsletters about fentanyl and how to use it safely. He says spreading the word among the drug-using community is the best way to prevent future deaths.

"These folks are going to use nevertheless. They have a dependency."