What Is CYP2D6 and CYP2C19 Testing for Psychiatric Drug Response?
Many antidepressant drugs are metabolized, or broken down, by two enzymes called CYP2D6 and CYP2C19. Drugs used to treat psychosis (antipsychotics) and Strattera® (generic name atomoxetine), an attention deficit with hyperactivity disorder (ADHD) drug, are also metabolized by the CYP2D6 enzyme. Changes in the genes that make these enzymes can cause you to metabolize drugs in an unexpected way.
Genetic testing can look for common changes in the CYP2D6 and CYP2C19 genes to find people who metabolize certain drugs faster or slower than usual. If you metabolize faster, you are called an "Ultrarapid Metabolizer". If you metabolize slower, you are called a "Poor Metabolizer". People who metabolize a little slower than usual are called "Intermediate Metabolizers".
Sometimes this information can be used by your doctor to predict if you are more likely to have side effects or less likely to get relief of your symptoms from certain drugs. The goal of this kind of testing is to help your doctor choose the best drug and dose for you with less trial and error.
| Drug Response | |
| Extensive Metabolizer | This is the most common result and is considered "normal". Extensive metabolizers have two genes that work normally. They make a normal amount of enzyme and usually have a normal drug response. |
| Intermediate Metabolizer | Intermediate metabolizers have at least one gene that isn’t working normally. They make less enzyme than normal. Usually there is enough enzyme to process most drugs relatively well, but there may be less response or more side effects from certain drugs. |
| Poor Metabolizer | Poor metabolizers have variants in both of their genes that cause neither gene to work normally. They make much less enzyme than normal or none at all. Poor metabolizers have a higher risk for side effects from some drugs and may need to avoid those drugs or take a lower dose. They may also need a higher dose of a drug, in the rare case where a drug has to be broken down before it works. |
| Ultrarapid Metabolizer | Ultrarapid metabolizers have extra copies of these genes. They make more enzyme than normal. Ultrarapid metabolizers may break some drugs down so quickly that the drug doesn't help at usual doses. They may also need a lower dose of a drug, in the rare case where a drug has to be metabolized before it works. |
