Older patients taking selective serotonin reuptake inhibitors, or SSRIs -- a class of antidepressants that includes Prozac, Paxil and Zoloft -- may be more likely to have intense suicidal thoughts or commit suicide, according to data published in the American Journal of Psychiatry. The study, conducted by researchers at the Institute for Clinical Evaluative Sciences in Toronto, showed that the suicide rate among seniors taking SSRIs was nearly five times higher than among those who were treated with other forms of antidepressants.

The study was conducted using patient prescription data, physician billing claims, hospitalization data and coroner's records for Ontario residents 66 and older between 1992 and 2000. There were about 1.2 million seniors whose information was examined, including 1,329 suicide cases. Among seniors who had committed suicide, more than two-thirds (907 people) had received no treatment. In the nine-year period, 73 patients taking SSRIs committed suicide, as did 349 patients taking other antidepressants.

David Juurlink, the study's lead author, noted, however, that it is difficult to distinguish the role of depression itself from the possible effects of the medication, In patients with major depression, he said, the "hazards of undertreatment almost certainly outweigh the risks of therapy."

In Canada, he added, there are approximately 16 million SSRI prescriptions issued annually, at a total cost of more than $1 billion.