Vancouver adds prescription heroin for hard-core addicts to its arsenal in the war against drugs this week, despite U.S. criticism that its trial is a sign of Canadian weakness in the battle against illegal drugs.

Medical researchers with the new clinic, North America’s first trial of prescription heroin, say their motives are not political. They hope to test if prescribing heroin can help addicts who have not been able to kick their habits through traditional programs like methadone treatment or abstinence.

The clinic starts taking applicants from drug addicts wanting to join the program on Thursday.

Vancouver, on Canada’s Pacific coast, is already the focus of a debate over drug treatment policy as the site of North America’s first government-sanctioned injection site for drug addicts, which opened in 2003.

The city includes the Downtown Eastside area, one of the poorest and drug-infested neighborhoods in Canada.

Dr. Martin Schechter, lead researcher for the North American Opiate Medication Initiative, said the new government-funded study is not designed to promote the legalization of heroin. The study is expected to last 21 and 24 months.

“We’re not an advocacy group. We’re researchers looking at a medical and scientific question,” Schechter said.

“If and when politicians and other decision makers have to look at the question of offering medically prescribed heroin, we’d like them to make that based on evidence not based on emotion.”

Schechter said heroin studies have already been conducted in Europe so this study could only be considered “radical” as the first in North America. The group will also open heroin clinics in Toronto and Montreal.

Officials in the White House’s Office of Drug Policy have dismissed the Canadian experiment as an example of what governments should not do to treat heroin addiction, and they advocate sticking with methadone treatment, where addicts are prescribed methadone as a substitute for heroin.

The study has the guarded backing of police officials in Vancouver, who hope for a reduction in the crime and health problems associated with injection drug use.

The researchers hope to enroll about 157 participants in Vancouver and 470 nationally.

Addicts will administer the drugs themselves under medical supervision, with half receiving pharmaceutical-grade heroin and half in a control group using methadone, a medicine that blocks heroin craving and prevents withdrawal symptoms.

The group receiving heroin will eventually be moved into the methadone treatment, and researchers will study which treatment method addicts are willing to stick with as well as their physical and mental health during the study.