Selective serotonin reuptake inhibitors (SSRIs) such as Prozac have been prescribed widely since they came on the market, but authors of Thursday's study suggested older drugs such as tricyclics may be better tolerated by some patients.

"SSRIs are therapies of choice for many practitioners, but there are a lot of options out there, and no particular class of drugs is routinely more effective than others," said Dr. Cynthia D. Mulrow, the study's lead author.

The San Antonio Evidence-Based Practice Center reviewed hundreds of clinical studies on 32 drugs, including three herbal treatments, for the Agency for Health Care Policy and Research, a division of the Department of Health and Human Services.

A closer look at drug side effects

Researchers found that roughly equal numbers of patients dropped out of clinical trials for newer and older antidepressants due to side effects. The SSRIs were more likely to cause diarrhea, nausea, insomnia and headaches. The older drugs had more adverse effects on the heart and on blood pressure, as well as dry mouth, constipation, dizziness, blurred vision and tremors.

Study authors looked for data on sexual dysfunction, a common complaint about the SSRI drugs, but were unable to find enough data to address that problem.

"What can make the difference is how well matched a given individual with depression is with a given treatment," said Dr. Matthew Rudorfer, who commented on the report in The New York Times.

Caution advised before use in children

Whether any antidepressant would work for children was still an open question, according to researchers, who could not find enough data on that issue.

And for mildly depressed people, there was not enough research to establish whether any of the antidepressants were effective. Still, authors said a few studies of dysthymia, a chronic low-level depression, suggested that SSRIs may help lift a patient's spirits.

Alternatives, including St. John's wort

Medical literature was reviewed for three herbal treatments -- kava kava, valeriana and St. John's wort -- but researchers were unable to find evidence of effectiveness yet for any of the herbal compounds.

However, St. John's wort "holds promise for mild to moderate depression and may have fewer adverse effects reported than older-generation antidepressants," said the study's authors. They also noted that a controlled, blinded clinical trial is underway to compare St. John's wort with an SSRI drug.

Depression and mood disorders affect an estimated one in five Americans sometime during a lifetime. The report described depressive disorders, including major depression and dysthymia, as serious, disabling illnesses.