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drug therapy

Antidepressants are by far the most common form of treatment for depression. Research shows, however, that the medication is effective only about half the time.

(The most potent treatment is a combination of antidepressant medication and psychological counselling.)

Patients often try several medications before they find one that works for them. Physicians also try to tailor their prescriptions to symptoms - for example, a patient with depression and insomnia will probably get an antidepressant that tends to induce sleepiness.

The most popular antidepressants in Canada are selective serotonin reuptake inhibitors (SSRIs). These drugs, best known under brand names like Prozac, Paxil and Zoloft (and largely sold now as generics), increase the level of serotonin, a neurotransmitter in the brain.

Last year, there were 22.6 million prescriptions for SSRIs, and total retail sales were $1.05-billion, according to IMS Health Canada, a private company that tracks prescription drug sales.

There have been attempts to determine which antidepressants - and SSRIs in particular - are most effective.

A study published earlier this year in The Lancet found that the best was sertraline (brand name Zoloft), with 69 per cent of patients responding to treatment. It was followed by escitalopram (Lexapro); studies found response rates ranging from 51 to 69 per cent.

The research was a meta-analysis, a compilation and analysis of 117 separate studies that were conducted from 1991 to 2007.

A second meta-analysis, published in the Cochrane Database of Systematic Reviews, came up with similar results, identifying sertraline as the superior drug in head-to-head comparisons with other SSRIs. Escitalopram was next best, though researchers noted that most studies on the drug were industry-sponsored and perhaps less reliable.

Sagar Parikh, a professor of psychiatry at the University of Toronto, said the findings have "enormous implications" because they allow practitioners to "identify the best treatments, identify individual side-effect profiles, explore costs and patients' preferences, and collaborate in identifying the best treatment for that patient."

Like all drugs, SSRIs have side effects, which can include weight gain, sleep disruption and sexual dysfunction. The drugs have also been associated with suicidal thoughts, particularly in young people.