MONDAY, Dec. 5 (HealthDay News) -- Newer antidepressants seem to be about as effective as one another, a new analysis indicates.

This suggests that the choice of which drug is appropriate for which patient should be made on the basis of such considerations as side effects, cost and patient preference.

"They're all equally effective," said Dr. David Schlager, a clinical assistant professor of psychiatry and behavioral science at Texas A&M Health Science Center College of Medicine.

"They're interchangeable except for side effects," he added, so psychiatrists do tend to "exploit the side-effect profile" to find suitable medications for individual patients, he added.

According to the background information in the new study, appearing in the Dec. 6 issue of Annals of Internal Medicine, some 27 million people in the United States had taken antidepressants as of 2005.

Most of these drugs are "second-generation" medications such as selective serotonin reuptake inhibitors (SSRIs), norepinephrine reuptake inhibitors (SNRIs) and related drugs.

SSRIs include the best-selling Prozac (fluoxetine) and Zoloft (sertraline). An example of an SNRI is Effexor (venlafaxine).

Led by Dr. Gerald Gartlehner, the analysis was funded primarily by the U.S. Agency for Healthcare Research and Quality.

Authors reviewed data from 234 previously published studies, all of them randomized trials that had included at least 1,000 participants each.

While there was no difference in drug effectiveness, there were distinctions in how quickly a drug took effect, side effects and quality of life.

For instance, the authors said, Remeron (mirtazapine) takes effect faster than Prozac, Zoloft, Paxil (paroxetine) or Celexa (citalopram).

Bupropion, which goes by Wellbutrin and other brand names, has fewer adverse sexual effects than Prozac, Zoloft, Paxil or Lexapro (escitalopram).

"If a patient has insomnia, you would pick something more immediately sedating," said Schlager, who is also a psychiatrist with Lone Star Circle of Care in Austin. "If the patient has decreased appetite and weight loss, you would pick something more likely to cause weight gain like mirtazapine."

Cost, of course, is another consideration.

"If one drug costs $200 a month and another costs $20, I don't see any reason why not to go with the latter," said Dr. Radu Saveanu, a professor of psychiatry at the University of Miami Miller School of Medicine.

Dosing is also important, he said, "because studies have shown that if patients have to take the drug less frequently, compliance is higher, which will make a big difference in terms of efficacy."

But given the similarity in effectiveness, prescribing antidepressants is still largely a trial-and-error process.

It's hoped that the next series of studies will provide guidance on which medications to try first.

"The real heart of the matter is, if they don't respond to one type of antidepressant, is there any guidelines about what you should try next?" Schlager said.

More information

The U.S. National Library of Medicine has more on antidepressants.