For almost eight years, drug addicts have walked into a nondescript green building in the heart of Vancouver's troubled Downtown Eastside, sat down in front of a mirror at one of a dozen dimly lit, metallic tables and injected drugs such as heroin into their veins.

And for much of that time, the community group that runs the supervised-injection facility known as Insite has been fighting a lengthy, complex -- and so far successful -- court battle to prevent the federal Conservative government from shutting it down.

This week, both sides head to the Supreme Court of Canada, which will decide whether Insite is a health-care facility under the jurisdiction of the provincial government and whether closing the site violates the rights of the impoverished drug addicts living in this country's poorest neighbourhood.

Supporters, including the British Columbia government, point to a body of peer-reviewed studies that have concluded Insite prevents overdose deaths, reduces the spread of HIV and hepatitis, and curbs crime and open drug use.

The federal government rejects that evidence, arguing the facility fosters addiction and runs counter to its tough-on-crime agenda.

The stakes for both sides are high, said Margot Young, a law professor who notes the high court's decision will affect not only Insite, but the possibility that similar sites could open across the country.

"It's easy to get caught up in the intricacies of arcane constitutional arguments, but the case is really about real people who are in need and who are among the most neglected groups in Canadian society," said Young, of the University of British Columbia.

"Many people are watching this closely to see how well the social interests of these individuals are going to be acknowledged and recognized at the Supreme Court of Canada."

Insite, the first supervised-injection site in North America, opened in 2003 after an epidemic rise in overdose deaths in the Downtown Eastside. It was allowed to operate after the Liberal government of the day granted the facility an exemption from federal drug laws.

When Prime Minister Stephen Harper's Conservatives took power, the government initially refused to say whether it would permanently extend that exemption.

Worried the Tories were preparing to order the site closed -- an assumption that later proved correct -- the Portland Hotel Society, which operates the site with provincial funding, asked a B.C. judge to allow it to remain open without the blessing of Ottawa.

The B.C. Supreme Court ruled in Insite's favour, and the B.C. Court of Appeal agreed, ruling Insite is a health-care facility under the jurisdiction of the provincial, not federal, government.

In the meantime, the site has remained open, but with an uncertain future.

"To us, it's not a political thing -- it's not a Liberal or an NDP or a Conservative thing -- it's just the right thing to do, and if it does shut, people will die," said Mark Townsend of the Portland Hotel Society.

"Across Canada, in jurisdictions where the public and the local governments want to do these things, because they think it would make things a bit better for addicts, that's what isn't happening. We've been bullied, so no one else is going to want to go through that."

Insite has 12 booths in its injection room and 30 beds in a detox and treatment centre upstairs, known as Onsite. Up to 800 drug users visit the site each day, according to statistics provided by the Portland Hotel Society, with the average user visiting 11 times per month. It is funded by the provincial government through the local health authority, with an annual cost of nearly $3 million.

There have been roughly 2,400 overdoses in the facility since it opened, but no deaths. The group says some of those overdoses would have been fatal if they happened outside on the city's streets and alleys.

Health Canada declined to comment while the case is before the Supreme Court, but after the first court decision in 2008, then-health minister Tony Clement made the Conservative government's position clear.

"In this case, we have given it due process, we've looked at all the evidence, and our position is that the exemption should not be continued," Clement said at the time, describing the scientific evidence as "mixed."

"In terms of the public policy, it was clear: A better thing to do is to treat people, to prevent people from going on the drugs in the first place."

In written submissions, Ottawa says the B.C. government and Insite are asking the court to create a health-care exemption in the criminal law, calling such a scenario "extraordinary." When two levels of government each claim jurisdiction -- in this case, the federal government over drug laws, the province over health-care -- the federal government should be given priority, it argues.

The B.C. government says a principle known as "interjurisdictional immunity" means a federal law can't encroach onto a core provincial role, such as health care, and the court should declare federal drug laws simply don't apply to supervised-injection sites.

B.C's health minister, Mike de Jong, said he plans to reiterate the province's support for Insite to his federal counterpart once Harper appoints a new cabinet. He said he already has evidence on his side, and hopes to soon have a Supreme Court of Canada decision behind him, as well.

"The decision (to open Insite) in the first place was rooted in the desire to reduce deaths and have positive health outcomes, and the evidence would seem to support that," de Jong said in an interview.

"I have always thought that this challenge is primarily a health challenge and needs to be addressed from that perspective."

The court will also consider whether Insite is protected under the Charter of Rights and Freedoms. The court will hear arguments that ordering the facility to shut down would violate drug addicts' rights to life, liberty and security of the person because, without Insite, they would be at greater risk of a fatal overdose.