The risk of suicide or suicide attempts among adults starting antidepressant therapy does not appear to vary according to the individual type or class of medicine, a US analysis has found.

In the cohort study reported in the May issue of Archives of General Psychiatry, a research team led by Dr Sebastian Schneeweiss of Brigham and Women’s Hospital and Harvard Medical School in Boston looked at health utilisation data in 287,543 adult (aged 18 years and over) residents of British Columbia in Canada who had initiated antidepressant therapy between 1997 and 2005.

A US Food and Drug Administration (FDA) advisory in October 2004 warned about the potential for increased risk of suicidal thoughts and behaviours among children and adolescents, the authors note.

This was followed by a black box warning on product labelling in 2005, which the FDA asked manufacturers to update in May 2007 to include increased risks of suicidal thoughts and behaviour among young adults aged 18-24 years during initial treatment with antidepressants (usually the first one to two months of therapy).

Last August, the FDA published an analysis showing that the risk of suicide associated with antidepressants was age-dependent, with people under 25 taking the drugs more than twice as likely to experience suicidal thoughts and behaviour than those on placebo.

After the FDA issued its initial advisory, subsequent analyses found no overall increase in the risk of suicidiality among adult antidepressant users, although these analyses and advisories have not provided patients, clinicians or policymakers with adequate guidance for treatment decisions, Schneeweiss et al say.

“Despite the widespread use of antidepressant medications, particularly selective serotonin reuptake inhibitors (SSRIs), there is inconsistent evidence that growth in antidepressant use has reduced the prevalence of suicidal ideation or suicide attempts during the past decade,” they add.

The cohort study sought to address whether the risk of suicide was consistent across all antidepressant classes and compounds, after adjustment for selection factors, or whether there were particular regimens with safety advantages that should be prescribed preferentially in adult populations.

The researchers found that, during the first year of antidepressant use, 846 adults in the cohort either attempted (751) or committed (104) suicide. Most of these events occurred within the first six months of starting treatment.

However, there were no clinically meaningful differences in the risk of suicide or suicide attempts among patients taking different classes of antidepressants, including SSRIs, serotonin-norepinephrine reuptake inhibitors, tricyclics and other newer and atypical agents. Nor were there any significant variations in risk between individual products, including fluoxetine (Prozac), citalopram (Cipramil), fluvoxamine (Luvox), paroxetine (Paxil) and sertraline (Zoloft).

“Our finding of equal event rates across antidepressant agents supports the US Food and Drug Administration’s decision to treat all antidepressants alike in their advisory,” Schneeweiss et al concluded.

“Treatment decisions should be based on efficacy, and clinicians should be vigilant in monitoring after initiating therapy with any antidepressant agent,” they recommended.