Elevated levels of these CYP enzymes in smokers, particularly in specific brain cell populations, may confer neuroprotective benefits by neutralizing neurotoxins—a hypothesis supported by the reduced risk of Parkinson’s disease observed in smokers compared to non-smokers, suggesting a potential neuroprotective function of CYP2D6 [32,243,244]. The gene discussed is CYP2D6; the disease is Parkinson disease.