What role does CYP2D6 play in Müdigkeit?

CYP2D6 is a cytochrome P450 enzyme primarily involved in metabolizing many drugs, including antidepressants, antipsychotics, opioids, and beta-blockers. Reduced enzyme activity ('poor metabolizer') can lead to higher drug levels, potentially causing fatigue as a side effect. Conversely, 'ultrarapid metabolizers' may clear drugs too quickly, leading to subtherapeutic dosing and inadequate treatment of underlying conditions, which can also manifest as fatigue. However, a direct causal role of CYP2D6 variants in fatigue independent of medication is not well established. Evidence is mainly mechanistic and from pharmacokinetic studies or case reports, not from large-scale human trials. MyBody-X may test CYP2D6 variants, but linking them to fatigue is speculative without a medication context. In the absence of drug intake, the contribution of CYP2D6 to fatigue is likely minimal.