CYP2D6 is a gene that provides instructions for making an enzyme involved in the metabolism of many medications. This enzyme helps break down drugs, including antidepressants, antipsychotics, and certain pain relievers, allowing the body to eliminate them effectively. Variations in the CYP2D6 gene can affect how individuals respond to these medications, leading to differences in effectiveness and side effects. The activity of the CYP2D6 enzyme can vary widely among individuals due to genetic differences. Some people are classified as "poor metabolizers," meaning they process drugs slowly, while others are "ultra-rapid metabolizers," processing drugs much faster. Understanding a person's CYP2D6 status can help healthcare providers tailor medication choices for better treatment outcomes.