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. Cytochrome P450 tests are generally used only when initial antidepressant treatments aren't successful.
Genotyping tests are also used in other areas of medicine. The 2D6 test can help determine whether certain cancer medications, such as tamoxifen for breast cancer, are likely to be effective. The 2C9 test can help determine appropriate dosing of the blood thinner warfarin (Coumadin) to reduce the risks of adverse effects.