Cytochrome P450 (CYP450) Tests - How & Why

Some of us respond differently than others to the same medications that we take, or we may experience different side effects from drugs. The way we respond can be due to the genes we have inherited.

The human body contains P450 enzymes to process medications. The P450 enzyme with the most variation in different people is the CYP2D6, which processes many antidepressants and antipsychotic medications. CYP450 tests are generally used only when initial antidepressant treatments aren’t successful.

Test Preparation

No preparation work is needed for the test. Fasting isn’t needed for this test.

Test can be either of the three ways.

  • Blood test. Blood is drawn from a vein in your arm.
  • Cheek swab. A cotton swab is rubbed inside your cheek to get a cell sample.
  • Saliva collection. You will be asked to spit saliva into a collection tube.


Results of a CYP2D6 test may show which of these four types applies to you:

  • Poor metabolizers. If you process a certain drug more slowly than normal because of a missing enzyme, the medication can build up in your system. This can increase the likelihood that it will cause side effects. You might still be able to benefit from these medications, but at lower dosages.
  • Intermediate metabolizers. If you have reduced enzyme function in processing drugs, you may not process some medications as well as normal metabolizers do. This can increase your risk of side effects and drug interactions.
  • Normal metabolizers (also known as extensive metabolizers). If the test shows that you process certain antidepressants normally, you’re more likely to benefit from treatment and have fewer side effects than people who don’t process those particular medications as well.
  • Ultrarapid metabolizers. In this case, medications leave your body too quickly — often before they have a chance to work properly. You’ll likely need higher than usual doses of medications.




* The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.