Montreal is going through an unprecedented wave of fatal drug overdoses that is spreading terror among users.

At least 56 overdoses linked to the intake of street drugs, including heroin and cocaine, have been reported in Montreal since May—18 of which were fatal. By comparison, there are usually an average of 1.3 deaths following drug injection per month in the city. Early reports show a number of these overdoses occurred after users injected heroin, but other substances are likely to be involved. Victims were between 20 and 61 years of age and were both regular and occasional users.

The situation has gotten so out of hand that Montreal's public health department has launched an investigation into the cases, and a prevention campaign has been set up encouraging users to use extra precautions such as testing their drugs and using in the presence of someone else.

"Users are feeling terrorized," said Dr. Marie-Ève Morin, an addiction specialist working at OPUS clinic in Montreal.

She thinks traffickers have wrongly manipulated the heroin batch currently circulating on the Quebec market.

"Either they didn't know what they were doing, or they made a mistake," Dr. Morin told VICE.

Fentanyl, a deadly substance that has been causing dozens of deaths in the US, has been found to be at play in at least one case, but lab tests have so far indicated that a highly concentrated heroin is more likely to be the main cause of the overdoses.

Montreal's drug traffic has been going through big shifts after one of the local mafias running the trade saw its leader disappear, as revealed in La Presse last week. According to La Presse, for years, the heroin market was dominated by a small number of experienced organizations: the Turkish mafia, some Iranian importers, a leader of the Italian mafia clan, and a branch of "traditional organized crime in Quebec" who exercised a quasi-monopoly. New, inexperienced traffickers have taken advantage of the chaos that followed the probable death of Turkish mafia leader Attilla Gascar, which has left the drug trade in shambles.

Increasing consumption of opioids (synthetic drugs such as oxycodone and codeine that resemble opiates like heroin and morphine) across North America has also changed the regional drug trade, especially since prescription drugs like Oxycontin have become more difficult to procure, and illegal labs have jumped in to fill the need. Last year Montreal police seized an unprecedented amount of synthetic drugs during a major bust, including three kilos of fentanyl.

"Cocaine is losing ground in favour of opioids," said Dr. Claire Morissette, from Montreal's public health department.

It is still unclear whether the current situation is temporary or not; in the meantime the debate around prevention has been amped up in light of the recent overdoses. Health professionals and community workers have been wondering why naloxone, a substance used to counter the effects of opiates and used to treat overdoses, is only available in Montreal's emergency rooms. Quebec's ministry of public health announced a plan to make naloxone available to paramedics, but this might take weeks to implement and would be of little help as overdoses following opiate intake can be fatal within minutes. Some think it would be more useful for users to carry a couple of doses around, should they witness an overdose.

"That the public health ministry hasn't made Narcan available to us baffles me," said Dr. Morin, referring to naloxone's trade name.

Others think the current wave of overdoses is just more proof that Montreal should open injection sites sooner rather than later, a project that has been stuck in bureaucratic procedures for months since it was announced in late 2013.

"This situation brings a new perspective on the utility of supervised injection sites," says Morissette.