Why it's done

Medications for depression are usually prescribed based on symptoms and medical history. For some people, the first antidepressant tried relieves depression symptoms and has tolerable side effects. For many others, however, finding the right medication takes trial and error. For some people, it can take several months or longer to find the right antidepressant.

Genotyping tests, such as cytochrome P450 tests, may speed up the identification of medications that are more likely to be better processed by your body. Ideally, better processing would lead to fewer side effects and improved effectiveness. CYP450 tests are generally used only when initial antidepressant treatments aren't successful.

Genotyping tests are also used in other areas of medicine. For example, the CYP2D6 test can help determine whether certain cancer medications, such as tamoxifen for breast cancer, are likely to be more effective. The CYP2C9 test can help determine appropriate dosing of the blood thinner warfarin to reduce the risks of adverse effects.

The field of pharmacogenomics is growing and many different types of genotyping tests are available. Tests differ widely by which classes of drugs they examine and how the tests are performed.