That’s what caused her death.

Gratton died of “acute methadone intoxication in the setting of ischemic heart disease,” according to the coroner’s report, which was given to the Star by Gratton’s husband.

Provincial guidelines for methadone treatment say someone in Gratton’s position should have received a much lower dose than she did. The coroner states in his report that other factors may have contributed to her death, including Gratton’s pre-existing high blood pressure. She ultimately died of a heart attack in hospital. Three doctors who reviewed the coroner’s report for the Star say it’s clear she died of a methadone overdose.

Gratton, a U.S. citizen and permanent resident of Canada who lived in London, Ont., was not serving a criminal sentence or awaiting trial, though she was treated the same as those who were. She had been sent to a maximum-security jail because the Canada Border Services Agency was contemplating deporting her and feared she would not show up for her deportation if it were ordered. The agency based its decision on Gratton’s criminal convictions from 2013, for which she was sentenced to six months of house arrest. Some have argued she should not have been detained in the first place.

The 50-year-old grandmother was found unresponsive in her cell at the Vanier Centre for Women in Milton just after midnight on Oct. 30, 2017. About 40 hours earlier she was given her first dose of methadone, a long-acting opioid often used to treat addiction to shorter-acting opioids. Gratton had depended on prescription painkillers for many years, but the jail’s medical staff was trying to wean her off them. She received her second dose of methadone the morning before she died.

“I suspect if the physician who prescribed this could do it over again, he or she would start on a lower dose,” said Dr. David Juurlink, a medical toxicologist and senior scientist at the Institute for Clinical Evaluative Sciences, and one of three opioid-specializing doctors who reviewed Gratton’s coroner’s report at the Star’s request. All agreed she should have been started on a lower dose of methadone or a different drug altogether.

Gratton’s death was ruled accidental. A coroner’s inquest has been ordered but has not been scheduled.

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The Star first reported on Gratton’s case last December, and again in March when two women who were incarcerated with Gratton came forward to raise concerns about her treatment in the jail. But this is the first time her official cause of death has been reported.

Herb Gratton, Teresa’s husband and partner of more than 30 years, said he is frustrated and angry, but he mostly just misses his wife. “The system had her,” he said in a recent interview. “They were supposed to be responsible.”

Herb, who is a Canadian citizen from the Caldwell First Nation, says this time of year is particularly difficult. His wife was the one who organized the family get-togethers and did most of the cooking.

“Christmas does not seem like Christmas,” he said. “I can’t find a reason to celebrate. I have my children, my grandchildren. But there’s a void. No matter who’s around or what’s around, I can’t fill it, you know?”

A mother of three who had lived in Canada since 2003, Teresa Gratton suffered from osteoarthritis and fibromyalgia, a long-term condition of the central nervous system that causes widespread pain. She relied on the opioid hydromorphone and was prescribed a high daily dose by her doctor months before she was incarcerated. When she couldn’t get her opioids from a doctor she got them on the street, her husband said. A month before her death she pleaded guilty to forging her doctor’s signature in an attempt to get an extended supply of hydromorphone. She also took several other prescribed medications, including ones for anxiety and depression.

The jail’s medical staff decided Gratton should not be on opioids. The coroner’s report references a physician’s note in Gratton’s medical file that reads: “SUD (substance use disorder), I agree, no indication for long-term opioid therapy.”

First they cut her dose by more than half. A week later they tapered her dose further and then withdrew her opioids completely for 10 days before giving Gratton her first dose of methadone.

Thirty milligrams, the amount Gratton received in each of her two doses, is the maximum starting dose for methadone treatment, according to guidelines published by the College of Physicians and Surgeons of Ontario. However, the guidelines state that if a patient has been “recently abstinent from opioids,” as Gratton was, the maximum starting dose should be no more than 10 milligrams. The guidelines do not specify how many days qualify as recent abstinence, but they do say that patients who have not used opioids “even for a few days” are at a higher risk of overdose.

The guidelines also state that patients who are also on benzodiazepines or any sedating drugs, as Gratton was, should be considered at a “higher risk for methadone toxicity” and therefore should be given a lower starting dose.

Two doctors, Dr. Abraham Shedletzky and Dr. Laura Middlestadt, are among the medical staff who work inside the jail. It’s not clear who oversaw Gratton’s treatment or if either doctor administered the methadone. The coroner’s report doesn’t name any doctor as being responsible for Gratton’s treatment. Middlestadt declined to comment for this story. Shedletzky did not respond to multiple interview requests.

Juurlink said he didn’t understand why the jail’s medical staff, even if they believed Gratton should be on a lower dose of opioids, would have tapered her off the drugs entirely. “Her brain and body would have become accustomed to that amount of hydromorphone,” he said. “She would have been physically dependent on it, and when you take it away people get horribly sick.” Tapering should be done slowly and generally with the patient’s consent, he added.

Even if there were compelling reasons to reduce Gratton’s opioid dose and replace it with methadone, Juurlink said someone in Gratton’s position shouldn’t be off opioids for as long as she was. “That’s 10 days of putting this patient through hell.”

Gratton wrote her husband regularly during her time in jail. In her letter she describes the agony of her withdrawal symptoms, which included vomiting, diarrhea, severe muscle pain, constant sweating and depression.

“I’d rather be dead than to keep going through this pain,” she wrote in one letter. “These doctors … think I don’t need to be on any of my narcotics. If something bad should happen to me please sue the hell out of them.”

The coroner’s report says that Gratton filed a complaint to the Office of the Ombudsman of Ontario regarding the reduction of her opioids by the jail’s medical staff. A spokesperson for the ombudsman said that for confidentiality reasons she could not confirm whether a complaint had been filed.

Juurlink also pointed to Gratton’s concurrent use of clonazepam, which she took to treat panic attacks, as a reason she should have been started on a much lower dose of methadone. Clonazepam belongs to the benzodiazepine class of drugs. It is a tranquilizer that, when combined with methadone, increases the risk of overdose.

“You have a one-plus-one-equals-five kind of effect,” Juurlink said. “They’re both depressants of the central nervous system and it’s really quite dangerous to combine opioids with drugs like that, especially for a patient who, for all intents and purposes, is opioid naive.” Juurlink said Gratton would have lost whatever opioid tolerance she might have had during her 10 days without the drug.

A spokesperson for Ontario’s Ministry of Community Safety and Correctional Services, which is responsible for provincial jails, said no one from the ministry would be interviewed for this story. They also declined to answer specific questions about Gratton’s case, citing the pending inquest.

The spokesperson provided a written statement, which reads, in part: “Decisions about health care matters are between inmates and medical staff. The ministry does not interfere with medical decisions or direct medical professionals.”

Dr. Ramesh Zacharias, the coroner, writes in his report that it’s unclear whether Gratton should be considered “a completely naive user in the context of methadone maintenance therapy.” Zacharias notes that although Gratton had not consumed opioids for 10 days before her first dose of methadone, “prior to that period she was a longtime user and abuser of hydromorphone.”

Dr. Meldon Kahan, medical director of the Substance Use Service at Women’s College Hospital, said it is “unusual” for just two doses of 30 milligrams of methadone to cause death. However, given Gratton’s recent abstinence from opioids and the fact she was on other sedating medications it “might have been more prudent” to start her on a different drug or a lower dose.

Kahan said it would have been better for the jail’s medical staff to prescribe buprenorphine, another long-acting opioid used to treat addiction, rather than methadone.

“It’s much safer than methadone,” he said. “It’s much safer than simply stopping the opioid, and it’s much safer than keeping them on the opioid that they’re already on.”

Juurlink agreed, calling buprenorphine “an infinitely safer medication.”

A ministry spokesman refused to say whether buprenorphine was available to doctors inside the jail.

Gratton died after suffering a heart attack in hospital roughly nine hours after she was found unresponsive in her cell. Zacharias writes in his report that he couldn’t attribute methadone intoxication as the sole cause of death because of uncertainties around Gratton’s tolerance, his inability to determine the peak concentrations of methadone in her blood when she lost consciousness, and because her body did not immediately respond to naloxone — a drug that can reverse the effects of opioids — when it was administered by paramedics. It’s not clear for how long Gratton had been unconscious when her cellmate, who had been sleeping, alerted jail guards.

Zacharias also notes that a methadone overdose can itself increase the risk of a heart attack.

The doctors who reviewed the report for the Star said it’s clear an overdose of methadone was the cause of death, whether or not she suffered other heart complications. Juurlink said that the vomiting and diarrhea Gratton experienced during her withdrawal would have left her with lower potassium and magnesium, which would have “amplified” the effects of methadone on her heart. “Methadone can kill you in more than one way,” he said.

Besides how she died, there are also questions about why Gratton was detained in the first place and why she was held in a maximum-security jail — questions that could be raised as part of the inquest.

The CBSA’s grounds for stripping her permanent residency were for “serious criminality,” which is defined in part as any conviction that leads to a “term of imprisonment” of more than six months.

Gratton came to be in police custody in September 2017 after she was arrested for shoplifting at Walmart, but the CBSA’s finding of “serious criminality” was related to convictions from 2013, when she pleaded guilty to forging a former employer’s signature on cheques for amounts ranging from $100 to $250. (Gratton admitted forging the signatures, but she believed the man owed her the money for house cleaning, according to a court transcript.) She also pleaded guilty to unlawfully being in the man’s house, although she did not break in. She was given a nine-month conditional sentence, which included six months of house arrest but no jail time.

The CBSA interpreted Gratton’s conditional sentence as a “term of imprisonment” of more than six months, meaning she would have no right to appeal her deportation. On Oct. 19, 2017 — 11 days before Gratton died — the Supreme Court of Canada struck down such interpretations, ruling it was unreasonable for immigration authorities to equate conditional sentences, such as house arrest, with jail time.

Immigration authorities have also not clarified why Gratton, who was not considered a danger to the public and had no history of violence, was classified as a “high-risk” detainee and sent to a maximum-security jail. By the CBSA’s own policies her minimal, non-violent criminal record should have made her eligible for the Immigration Holding Centre, a far less restrictive facility.

A CBSA spokesperson has said the agency decided maximum-security jail was a “better choice” for Gratton due to “various case-specific factors.” The spokesman would not explain the factors that led to their decision, citing a need to protect Gratton’s privacy.

The location of detention for immigration detainees is decided solely by the CBSA and not subject to any external oversight.

Brendan Kennedy is a Toronto-based investigative reporter. Follow him on Twitter: @BKennedyStar