How are CYP2D6 and fatigue related?

The direct relationship between CYP2D6 and fatigue is not well established in the scientific literature. CYP2D6 is a key phase I drug-metabolizing enzyme responsible for breaking down many medications, including antidepressants (e.g., SSRIs, tricyclics), antipsychotics, opioids, and beta-blockers. Depending on the genotype (poor, intermediate, normal, or ultrarapid metabolizer), drug concentrations can vary significantly. Inadequate or excessive drug exposure may lead to fatigue as a side effect. For instance, poor metabolizers may experience sedation from higher levels of amitriptyline or codeine. However, no robust studies demonstrate a direct, drug-independent link between CYP2D6 variants and general fatigue. Evidence is limited to pharmacogenetic case reports and association studies with small effect sizes. Consumer DNA tests that claim such a connection often overstate the science. Clinically, the main relevance of CYP2D6 is in guiding medication dosing, not as a fatigue biomarker. Safety note: Do not change medication based on a genetic test without medical supervision.