The move by Prime Minister Justin Trudeau's government last week is another step in reversing the policies of the previous government, run by Conservatives, and taking a less draconian approach to the fight against addiction and drug abuse.

In April, the Trudeau government announced plans to legalize the sale of marijuana by next year, and it has appointed a task force to determine how marijuana will be regulated, sold and taxed. The government has also granted a four-year extension to the operation of Insite, a supervised injection site in Vancouver where addicts can shoot up street-obtained drugs in a controlled environment. The previous government had tried in vain for years to shut down that clinic.

The latest decision means that any physician in Canada can now apply to Health Canada for access to diacetylmorphine, as pharmaceutical-grade heroin is known, under a special-access program. The government says that this kind of treatment will be available for only a small minority of users “in cases where traditional options have been tried and proven ineffective” and that it is important to give health-care providers a variety of tools to face the opioid-overdose crisis.

Scott MacDonald, the lead physician at the Crosstown Clinic, welcomed the federal government’s decision. The clinic, which is funded by the British Columbia provincial government, opened in 2005 to conduct a clinical trial of prescription heroin and has operated ever since. It provides diacetylmorphine to 52 addicts under a special court-ordered exemption but expects that number to double over the next year if supplies can be obtained. The court order came after a constitutional challenge of a 2013 effort by the previous government to stop distribution of the drug.

Colin Carrie, a Conservative member of Parliament and the party's spokesman on health policy, said his party remains adamantly opposed to the use of prescription heroin as a treatment option for addicts. "Our policy is to take heroin out of the hands of addicts and not put it in their arms."

MacDonald says his patients are usually long-term users — one has been on heroin for 50 years — for whom standard treatments such as methadone and detox have failed after repeated attempts. “Our goal is to get people into care,” he said. (The clinic also treats another group of addicts with hydromorphone, a powerful painkiller.)

The demands of the program are high. Patients must come into the clinic two or three times a day for injections, which is disruptive for those who wish to work or take care of their families. Still, the dropout rate is relatively low. The patients are healthier, and participation in the program drastically reduces their participation in criminal activities, sharply cutting the cost to the criminal justice system.

Crosstown’s approach has garnered increasing attention in the United States, with MacDonald appearing in June to testify before a Senate committee on Capitol Hill. But the approach remains controversial. After making a presentation recently in Boston, he got a positive response from some doctors but noted that “there were physicians who would not even come up and talk to me.”