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.