People diagnosed with clinical depression face a rough road to recovery. Many spend weeks, months, or even years trying different antidepressants in hopes of finding the right medication -- one that cures their depression without insomnia, headaches, or other side effects.

Now two new kinds of genetic tests, one already available and one several years away, could help doctors and patients avoid this wearisome process.

"It's very difficult to have to take a drug for weeks, then get off it and try a new one," says Julio Licinio, a psychiatrist who studies the genetics of depression at the University of California, Los Angeles. "If we had any kind of marker that would tell us which person would respond to which drug, treatment would be much more efficient than it is now."

Psychiatrists in the United States recently got a new set of tools to match the drug to the patient: genetic tests that can predict if a person will have side effects with a particular drug.

One such test, made by Swiss-based Roche Diagnostics, was approved by the U.S. Food and Drug Administration in January 2005 and was recently made available to doctors. The Roche test detects genetic variants for two enzymes involved in the break down of 25 percent of prescription drugs, including pain medications, beta-blockers, and antidepressants. Someone who has a form of the enzyme that breaks down a drug slowly is more likely to experience side effects at the standard dose because the drug builds up in the body. At the other extreme, someone who has a form of the enzyme that breaks down the drug very quickly may not have the medicine in the body long enough to do its job.

 [Click here to view an image of the Roche tester.]

Experts predict that one of the major potential uses for the test will be in treating depression, because people react so variably to different antidepressants, and side effects are one of the main reasons people stop these drugs.

This test is one of the first attempts to take personalized medication to the clinic," says Jose de Leon, a psychiatrist at the University of Kentucky in Lexington, who is studying the effectiveness of these tests. Specifically, he found that people with a mutation in one of these enzymes were more likely to stop taking the drug risperidone, an antipsychotic, because of adverse effects. He's now working with Roche to see how efficient and cost effective the tests are in psychiatric hospitals.