Cytochrome P450 (CYP450) tests

Your doctor may use cytochrome P450 tests (CYP450 tests) to help determine how your body processes (metabolizes) a drug. Our bodies contain numerous P450 enzymes to process medications. Because of inherited (genetic) traits which cause variations in these enzymes, medications affect each person differently.

The P450 enzyme with the most variation in different people is the 2D6, which processes many antidepressants and antipsychotic medications. By checking your DNA for certain gene variations, cytochrome P450 tests can offer clues about how your body may respond to a particular antidepressant. Other cytochrome P450 tests are available for other enzymes.

Cytochrome P450 and other genetic tests (genotyping tests) are becoming more common as doctors try to understand why antidepressants help some people and not others. While their use might be increasing, there are limitations.


Why it's done How you prepare What you can expect Results

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.

© 1998-2015 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. Terms of use