TORONTO - First Nations leaders say a health crisis is about to be unleashed on northern Ontario reserves because thousands of residents addicted to OxyContin will soon be cut off from the prescription opiate.

The maker of OxyContin, which is up to twice as strong as morphine, will stop manufacturing the drug in Canada at the end of the month. As of March 1, Purdue Pharma Canada will replace OxyContin with a new formulation called OxyNEO.

OxyContin, taken orally in pill form, is a long-acting form of the highly addictive opioid oxycodone. But when the pill is chewed or crushed, then injected or inhaled, it produces a "heroin-like euphoria," Health Canada says.

OxyNEO will also be made with oxycodone, but it's formulated to make abuse more difficult: the tablet is hard to crush and when added to liquid, it forms a thick gel that stops oxycodone from being extracted for injection.

Leaders of Ontario's Nishnawbe Aski Nation, or NAN, said that with no OxyContin available, those addicted to the drug will go into withdrawal.

"It scares me. It's going to be a catastrophe," said NAN Chief Stan Beardy, stressing that there is potential for a "mass involuntary opiate withdrawal" on the horizon.

"I don't think governments understand the severity of addictions we're talking about here," Beardy said in an interview Thursday.

NAN Chiefs-in-Assembly declared a state of emergency over the issue in November 2009 and have since made repeated requests for assistance from Health Canada and the Ontario Ministry of Health and Long-Term Care.

On Feb. 6, it was reported that almost 2,000 members of Matawa First Nations communities were addicted to opioids. In late January, the chief of the Cat Lake First Nation declared a state of emergency, saying an estimated 70 per cent of community members had opioid addictions -- including children as young as 11.

NAN Deputy Chief Mike Metatawabin said the number of Nishnawbe Aski Nation community members addicted to OxyContin "is staggering." NAN estimates that at least 10,000 people living on reserves are addicted to OxyContin and will suffer withdrawal when the drug is no longer available.

Symptoms can include severe stomach upset, muscle and bone pain, anxiety, increased heart rate and blood pressure, and depression and thoughts of suicide.

"These people will be very, very sick," said Benedikt Fischer, director of the Centre for Applied Mental Health and Addictions at Simon Fraser University in Vancouver.

Without treatment to help deal with the addiction, a public health catastrophe is imminent, Fischer predicted Thursday.

"There are thousands of addicted individuals with rapidly shrinking supplies -- likely leading to massive increases in black-market prices, use of other drugs, needle use sharing and crime," he said.

Unable to obtain OxyContin, addicts will likely turn to illicit drugs such as heroin, cocaine and crack, Fischer speculated. Needle-sharing would increase the risk of transmission of such infectious diseases as hepatitis C and HIV.

While some OxyContin has been diverted from prescriptions written by doctors, much comes via drug traffickers, sewn into baby blankets and secreted in false bottoms of pop cans. Each pill reportedly can sell for hundreds of dollars apiece.

Despite security checks of goods coming onto the reserves -- many of them so remote that they can be reached only by airplane -- "a lot of those drugs still find their way into our communities," said Beardy.

And he said the drug use is destroying many families and communities in the Nishnawbe Aski Nation, an organization representing 49 First Nation communities covering two-thirds of Ontario, including the James Bay area.

"We have never in history had such a high number of our children in care," he said, explaining that many of those addicted are young parents who are unable to look after their children.

"In many cases, there's no furniture because they sell off all their furniture, there's very little food, there's no appliances in many cases. It's very severe."

Metatawabin said problems with addiction and withdrawal will be especially intensified in these remote northern communities, where there is no access to detox and treatment programs.

"It is time for both levels of government to respond with programs and services that are urgently required to implement emergency strategies," he said.

But a spokesman for Health Canada said there is little concern about withdrawal when people taking OxyContin switch to OxyNEO, and when taken as prescribed by a doctor.

"However, it is possible that some clients who obtained OxyContin through other sources may go into withdrawal when OxyContin is removed from the Canadian market and they are unable to find another source of supply," Alastair Sinclair said by email. "This is a concern for any individual who obtains and uses OxyContin outside of appropriate medical indications."

Patients who currently qualify for OxyContin coverage will continue to have access to OxyNEO, he added.

But he noted that data from the Non-Insured Health Benefits (NIHB) program, which covers the cost of prescription drugs for reserve members, shows that fewer than 100 NAN members registered with the program put in claims for OxyContin.

Health Canada does have support available for those experiencing withdrawal, Sinclair said. The NIHB program provides coverage for methadone and suboxone, drugs used for the treatment of opioid withdrawal.

"The NIHB Program recognizes that there are situations where clients may not have access to methadone ... Given the remote location of many (reserves), access to methadone treatment is a significant issue. In such instances, the NIHB program reviews requests from health providers on a case-by-case basis and will provide coverage for suboxone to help ensure First Nations clients have access to this drug without leaving their community."