TORONTO -- Bariatric surgery is successful in significantly reducing weight for most people who undergo the procedure. But for a small proportion of patients, the operation fails to achieve hoped-for results -- and that can lead to potentially dire consequences, researchers say.

A study by the Institute for Clinical Evaluative Sciences (ICES) found that in the first few years after bariatric surgery, there's an increased risk of attempted suicide in patients for whom the procedure didn't work, suggesting the need for prolonged psychological followup.

Researchers say the operation is an effective treatment for morbid obesity, with an estimated 60 to 80 per cent reduction in weight within the first year for many patients. The procedure is also considered safe, with death rates averaging less than one per cent.

"Bariatric surgery in many cases is an extremely successful operation," said principal researcher Dr. Donald Redelmeier, an internal medicine specialist at Sunnybrook Health Sciences Centre in Toronto. "The average patient loses a lot of weight and some patients even get their diabetes cured."

But for an estimated one to two per cent of patients, the results are disappointing, he said.

For such obese patients, that can lead to depression and despair because they lose hope of ever being able to shed their excess pounds, said Redelmeier, a senior scientist at ICES.

"They've played that card once.... Once you go for bariatric surgery, in some cases it's the end of the line."

Redelmeier recalled one patient he saw in Sunnybrook's emergency department who had attempted suicide with a drug overdose.

The woman had undergone bariatric surgery two years earlier, which had failed to help her lose weight.

"And she really was so depressed about it. She had just suffered at home and terminated relations with her surgeon, her family doctor and her previous psychiatrist," he said.

"She was classic for suffering in silence because of the element of shame and disappointment."

Bariatric surgery is becoming more common in Canada, according to statistics from the Canadian Institute for Health Information (CIHI). In 2013-14, hospitals performed more than 6,500 operations, up from about 1,600 in 2006-07.

Those who qualify have failed to lose weight with diet and exercise and are morbidly obese, with a body mass index of at least 40, or a BMI of 35-39 with a weight-related health condition like Type 2 diabetes, high blood pressure or severe sleep apnea. Close to 80 per cent of patients are women, and their average age is 45.

The procedures -- adjustable gastric banding, sleeve gastrectomy and gastric bypass -- are intended to sharply restrict the amount of food a person can physically consume in order to shrink their weight.

Guidelines emphasize that prospective patients be mentally and emotionally prepared for the surgery and understand its benefits and limitations, as well as being committed to lifelong adherence to lifestyle changes and followup once the surgery is completed, CIHI says.

The ICES study, published Wednesday in the journal JAMA Surgery, examined health records for 8,815 Ontario adults who had undergone bariatric surgery between 2006 and 2011.

Researchers identified 111 patients who had 158 "self-harm emergencies" during the study period, with an increased number occurring during the three years following surgery, compared with the three years before.

Most suicide attempts involved intentional overdose with prescription drugs. About half the patients required hospitalization.

Overall, the relative risk of self-harm emergencies rose by about 54 per cent after bariatric surgery, compared to before surgery. Patients aged 35 or older, with a lower income or living in a rural area had the highest risks of attempted suicide.

"It's a particular concern in that it doesn't show up immediately," said Redelmeier. "For the first couple of months after the surgery, there's no increase whatsoever. It mostly begins to appear in the second and third year.

"And that's where we think there's a need for much greater followup," he said. "It's after the first year ... often the psychologists and the social workers have moved their interest onto other cases.

"That's when there seems to be some missed opportunities for intervention."

Any patient who is disappointed with the results of their bariatric procedure should go back to their surgeon or affiliated mental health-care providers if they develop anxiety or depression, Redelmeier urged, "so it doesn't end up leading to a suicide event."

"You're not alone after the surgery is over," he said, "even if the results are not a success."

In an accompanying commentary in the journal, Carol Lindsay-Westphal and Dr. Amir Ghaferi of the Ann Arbor Veterans Administration Healthcare System in Michigan say there is no minimum standard for continued psychological evaluation for this uniquely vulnerable group and "post-operative followup rates in general have been poor."

"Bariatric surgery is more than just an operation," they write, referring to the need for patients to completely overhaul their lifestyle. "It is time we recognize and treat it is as such."