A US study says there is a higher risk of people attempting to take their own lives after undergoing weight-loss surgery.

Those who undergo surgery for weight loss may face a 50-per-cent higher risk of attempting suicide after the operation, according to a study.

The research involved more than 8800 people in Canada and is published in the Journal of the American Medical Association Surgery on Wednesday.

Those in the study were followed for three years before and after they underwent bariatric surgery to alleviate morbid obesity, an epidemic in wealthy nations, where as many as six per cent of the population is affected.

While researchers have long known that mental health problems can be common in people who are severely overweight, they have not been able to pinpoint whether risks of self-harm existed before surgery or rose afterward.

The actual number of self-harm emergencies among the 8800 people was low - 111 patients had 158 such emergencies.

But researchers found that the risk of these emergencies increased significantly - by approximately 50 per cent - after surgery.

"Intentional self-poisoning by medications was the most common mechanism of attempted suicide," said the study.

Other methods of self-harm included alcohol, physical trauma and poisoning by toxic chemicals.

According to lead author Junaid Bhatti, of the Sunnybrook Research Institute in Toronto, the findings suggest a need for more careful follow-up of bariatric surgery patients.
Some 200,000 such operations are performed annually in the United States.

"These adverse events undermine the overall benefits of bariatric surgery," said Bhatti.

Nearly all the self-harm emergencies occurred in patients who had a history of a mental health disorder.

The study did not identify specific reasons for the spike in self-harm attempts.

But experts know that shrinking the size of the stomach via surgical means can also alter alcohol metabolism and may boost risky behaviour as a result.

An accompanying commentary by Amir Ghaferi and Carol Lindsay-Westphal, of the Ann Arbor Veterans Administration Healthcare System in Michigan, pointed out that bariatric surgery patients experienced twice the number of self-harm emergencies compared with the average population and four times the suicide rate.

"Most self-harm emergencies occur in the second and third postoperative years," Ghaferi and Lindsay-Westphal wrote, adding that "there is currently no minimum standard for psychological follow-up" and postoperative follow-up has generally been poor.

"Bariatric surgery is more than just an operation," they wrote.

"It is time we recognise and treat it as such."

Other experts said the findings should lead to more intense screening of potential patients.

* For support and information about suicide prevention, call Lifeline on 13 11 14 or the Suicide Call Back Service on 1300 659 467