Post-menopausal women on antidepressants may be increasing their chances of suffering a stroke and dying prematurely, a study released on Monday suggested.

The findings emerged from the federally funded Women's Health Initiative, one of the nation's largest and most comprehensive studies of women's health. The study followed 136,293 post- menopausal women, age 50 to 79, for about six years. Around 5,496 developed depression and were treated with antidepressant medication.

During the span of follow-up, the women on antidepressants were 45 per cent more likely than those not on such medication to have a stroke, and 32 per cent more likely to die of any cause. Women on depression medication were more prone to hemorrhagic strokes.

No difference in stroke risk was found between the two major classes of antidepressant, selective serotonin reuptake inhibitors (SSRIs), such as Prozac, and tricyclic antidepressants (TCAs). However, SSRIs were more associated with bleeding in the brain.

The absolute risk of stroke was very small - 0.43 per cent a year versus 0.3 per cent for women not on antidepressants. But because so many people take the pills, even this could have a significant impact at the population level, said the scientists. The findings are reported in the journal Archives of Internal Medicine.

Lead researcher Dr Jordan Smoller, from Massachusetts General Hospital in Boston, said, "While this study did find an association between antidepressants and cardiovascular events, additional research needs to be done to determine what it signifies.