Evidence check: CYP2C19 in the context of Müdigkeit

CYP2C19 is a cytochrome P450 enzyme responsible for metabolizing many drugs, including clopidogrel, proton pump inhibitors, and certain antidepressants. Genetic variants (e.g., *2, *3, *17) result in different metabolizer phenotypes (poor, intermediate, extensive, ultrarapid). A direct causal link between CYP2C19 genotype and fatigue in healthy individuals is not supported by robust human studies. Fatigue may occur indirectly when drugs are metabolized more slowly due to genotype, leading to higher drug levels or increased side effects. For example, poor metabolizers of antidepressants like escitalopram or amitriptyline may report fatigue more frequently. The evidence is primarily mechanistic, derived from pharmacogenetic studies rather than population-based investigations of fatigue itself. Direct-to-consumer tests claiming a connection between CYP2C19 and fatigue without a medication context overstate the current science. Clinically, CYP2C19 genotyping is most useful for guiding drug dosing, not for predicting fatigue. Therefore, the evidence is weak and mechanistic. Caution is warranted against overinterpretation of genetic test results.