CYP450 tests may help determine how your body metabolizes an antidepressant based on how genes affect your body's response to medication.
Your doctor may use cytochrome P450 (CYP450) tests to help determine how your body processes (metabolizes) a drug. The human body uses cytochrome P450 enzymes to process medications. Because of inherited (genetic) traits that cause variations in these enzymes, medications may affect each person differently.
Drug-gene testing — also called pharmacogenomics or pharmacogenetics — is the study of how genes affect your body's response to medication. Tests look for changes or variations in these genes that determine whether a medication could be an effective treatment for you or whether you could have side effects from a specific medication.
The cytochrome P450 enzyme includes the CYP2D6 enzyme, which processes many antidepressants and antipsychotic medications. By checking your DNA for certain gene variations, CYP450 tests can offer clues about how your body may respond to a particular antidepressant. CYP450 tests can also identify variations in other enzymes, such as the CYP2C19 enzyme.
CYP450 and other genetic tests (genotyping tests) are becoming more common as doctors try to understand why antidepressants help some people and not others. While the use of these tests might be increasing, there are limitations.
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.
You won't need to fast or have any special preparations before the procedure.
For cytochrome P450 tests, a sample of your DNA is taken, using one of these methods:
Getting the DNA sample should take just a few minutes. Then your sample is sent to a lab where your DNA is analyzed for specific genes.
It usually takes several days to a week to get the results of cytochrome P450 tests. You and your doctor can discuss the results and how they might affect your treatment options.
CYP450 tests give clues about how well your body processes a drug by looking at specific enzymes. The results can be classified according to how fast you metabolize a specific medication. For example, results of a CYP2D6 test may show which of these four types applies to you:
CYP450 testing isn't useful for all antidepressants, but it can provide information about how you're likely to process a number of them. For example:
Although they have potential, CYP450 tests have limitations:
Despite the limitations, some doctors use CYP450 tests and think they're helpful. However, these tests aren't meant to be the only way to determine which antidepressants to try. They're just one tool that may help. Trying antidepressants based on your medical history and symptoms is still the standard method for identifying the best medication for your needs.