"Our study confirms the belief that the diagnosis and treatment of depression have been impacted by the advent of selective serotonin reuptake inhibitors (SSRIs)," said Randall Stafford, MD, assistant professor of medicine at Stanford University School of Medicine and lead author of the latest report. "Findings show that the quality of care received by depressed patients has improved since the introduction of this class of medications in 1988." The study appeared in the April 29 issue of the Primary Care Companion to the Journal of Clinical Psychiatry.

SSRIs are one of several categories of antidepressants. Although medications in each category are effective in treating the disease, SSRIs (including well-known brands such as Prozac, Paxil and Zoloft) have fewer side effects than the others. Stafford noted that patients who take other types also face a greater risk of overdose, along with more side effects such as weight gain, stomach irritation and dry mouth.

The safety profile and relatively limited side effects of SSRIs make them attractive to both physicians and patients, Stafford said, and as a result they are the most prescribed category of antidepressant in the country. Stafford's team conducted the study to examine the drugs' popularity among physicians and to more closely examine their impact on treatment of depressive illness.

"Past studies have focused on broader changes in depression treatment, but we wanted to go beyond this and look at the relationship between SSRIs and other medications," he said. "There was a perception that treatment had changed since the advent of SSRIs, and we wanted objective information to go along with this."

To analyze prescribing trends, Stafford turned to diagnosis and treatment data from the National Disease and Therapeutic Index, a survey of office-based physicians. Stafford and his team selected visits by patients with depression-related diagnoses over the period of 1989 to early 2001; the sample of visits ranged from 3,901 in 1989 to 6,385 in 2000.

After analyzing the data, Stafford found that 70 percent of patients diagnosed with depression in 1987 (the year before SSRIs were introduced) were treated with antidepressant medication, while 89 percent were treated with medication in 2001.

The type of antidepressant prescribed changed dramatically over this time period as well. In 1987, the most commonly prescribed drugs were from a group known as tricyclics; of the treated patients, 47 percent were given this type. By 2000, only 2 percent of patients received tricyclics.

The study shows that SSRIs were rapidly adopted by physicians - in 1989, after just one year on the market, Prozac was prescribed to 21 percent of patients. Within six years of introduction SSRIs were the most highly prescribed type for depression. Stafford said this is unusual because physicians often "take their time to fully adopt recommended drugs."

"There is a perception that SSRIs are definitively better - even though they've never been shown to treat depression more effectively than other antidepressants," he said. "The perceived superiority probably stems from the drugs' fewer side effects, their promotion by manufacturers and greater public acceptance of these medications."

The study also shows that the number of physician visits by patients for depression increased from 14.4 million in 1987 to 24.5 million in 2001. Although Stafford said this increase was likely due to a number of factors, the advent of SSRIs certainly played a major role. "If you don't have medications you feel comfortable prescribing, your motivation for diagnosing someone as depressed is lower," he said. "Physicians feel comfortable with the treatment options so they're more likely to diagnose and treat their patients."

Stafford noted that past studies have shown that depression is widely underdiagnosed and undertreated in the United States, so the increase in the number of people being treated is encouraging. "SSRIs are helping to improve the quality of care for people suffering from depression," he said.