The treatment cohorts were generally comparable after matching with regard to age at PD diagnosis, gender, average disease duration, Charlson comorbidity score, GP consultations in 12 months prior to treatment initiation and other anti‐Parkinson's drugs (MAO‐B inhibitors, amantadine, apomorphine, Catechol‐O‐methyl transferase [COMT] or decarboxylase inhibitors) prior to treatment initiation. The gene discussed is COMT; the disease is Parkinson disease.