Antidepressant treatment is an inexact science, so make it collaborative.

Antidepressant treatment is an inexact science, so make it collaborative.(ENDOSTOCK/FOTOLIA)

Your doctor needs to consider your current physical symptoms and condition when prescribing an antidepressant or mood stabilizer. If you have chronic insomnia, for example, she should obviously steer clear of the medications that list this side effect.

Medications you're already taking can influence your doctor's decision: SSRIs (selective serotonin-reuptake inhibitors) can interact with antihistamines, for example, triggering a racing heart and other potentially dangerous symptoms.

How doctors prescribe antidepressants
"If a person asks for a specific antidepressant, I will often prescribe that one, unless there's a clear reason not to," says John Herman, MD, a psychiatrist at Massachusetts General Hospital and associate professor at Harvard Medical School, who says that this is one way to put a patient at ease. "If we can, we'll go with something that they're already familiar with, or that a friend is taking."

Maurizio Fava, MD, professor of psychiatry at Harvard Medical School, asks whether people have a history of prior treatment with a particular drug, because if it worked in the past, it might work again.

Depression may have a genetic basis, at least in some people. So if a patient tells Dr. Fava that a certain SSRI or atypical antidepressant worked in a parent or sibling, he may prescribe that one first.

[ pagebreak ]"Some people ask me not to put them on an antidepressant that could lead to weight gain, sexual dysfunction, or sleep problems," he says. People react differently to antidepressants, and it's not possible to predict who will experience which side effect.

Doctors can use a few rules of thumb, though. Antidepressants that are most likely to cause weight gain are Remeron and Paxil. It's not clear why certain drugs add pounds, though some experts believe they stimulate appetite and/or slow metabolism. According to a large report issued in 2007 by the U.S. Department of Health and Human Services, the worst offender is Remeron, which adds an average of 7% of body weight.

How long to take an antidepressant
Once you find the drug or drug combination that works, your doctor will probably recommend that you take the drug for another four to six months, if you have not previously had a depressive episode (if you have, you may be on antidepressants for longer). At that point the doctor may wean you off the medication by progressively lowering the dose over the course of several weeks.

Never discontinue your medication abruptly, and don't stop taking an antidepressant without guidance from your doctor. A gradual approach reduces the risk of side effects associated with stopping treatment and makes it easier for you to get back on a full dose if your symptoms return.

If your depression was severe, your doctor may recommend that you stay on the drug for months, years, or forever. Studies suggest that the relapse rate for severe depression may be as high as 70%.