CYP2C19 is a gene that provides instructions for making an enzyme involved in the metabolism of various medications. This enzyme helps break down drugs such as clopidogrel, omeprazole, and certain antidepressants, allowing the body to use them effectively. Variations in the CYP2C19 gene can affect how individuals respond to these medications. Some people may be "poor metabolizers," meaning the enzyme works less effectively, while others may be "ultra-rapid metabolizers," leading to faster drug breakdown. Understanding these differences can help healthcare providers tailor treatments for better outcomes.