Canadians rank among the most prolific users of antidepressants in the world, but new research has linked the widely-prescribed medications to an increased risk of premature death.

A study led by researchers at McMaster University in Hamilton, Ont., found that the risk of early death increased by 33 per cent in people who take antidepressants, compared to non-users.

Many antidepressants block the absorption of brain chemical serotonin, which affects mood. But serotonin is also absorbed by other organs besides the brain, and blocking it could have negative effects on body function, researchers say.

Their findings were based on a meta-analysis of 16 studies involving a total of 378,000 people. The analyzed studies looked at antidepressants and death rates.

While many of the studies did not report exact causes of death among antidepressant users, those that did showed a wide range of causes, from heart attacks and stroke to accidents, lead study author and McMaster University professor Paul Andrews said.

Deaths involving accidents were not surprising because “we know that antidepressants have negative effects on cognitive functioning as well,” Andrews told CTV News Channel on Monday.

Because depression itself is associated with an increased risk of death, the researchers isolated that factor when looking at the death rates.

They also concluded that, while antidepressants appear to be harmful in the general population, their use was less risky in people who already have cardiovascular disease. That’s because antidepressants could have a blood-thinning effect.

While some psychiatrists are defending the importance of antidepressants and calling the McMaster study alarmist, Andrew said that many antidepressant safety studies were done within a limited time period and before the drugs’ long-term effects could be fully understood.

He and his colleagues say further investigations into antidepressants’ effects on mortality are needed. 

In 2011, Canada reported the third-highest level of antidepressant use among 23 countries, according to a report by the Organisation for Economic Co-operation and Development (OECD). The report said Canadians consumed 86 daily doses of antidepressants per 1,000 people, a rate lower only than those reported in Australia and Iceland. However, the Canadian numbers were based only on data from Manitoba and Saskatchewan.

Andrews said there are some alternatives to antidepressants, such as psychotherapy, or “talking therapy,” which used to be the most common treatment for depression.

“(Psychotherapies) don’t have the negative physiological effects…and they work just as well in the short term,” he said.