Objective To test the hypothesis of an increased incidence of antiparkinson drug prescribing or Parkinson disease (PD) diagnostic codes after chronic lithium treatment compared with chronic valproic acid or antidepressant treatment among older adults.

Methods A retrospective cohort study using healthcare administrative databases in Ontario, Canada included 1,749 lithium users, 1,787 valproic acid users, and 285,154 other antidepressant users ≥ 66 years old having used the drug continuously in monotherapy for at least 1 year. Outcome measures were start of (1) a dopaminergic medication (levodopa or a dopamine agonist), (2) any antiparkinson drug (levodopa, dopamine agonists, anticholinergic medication, amantadine, monoamine oxidase B inhibitors), (3) any antiparkinson drug or a diagnostic code for PD, and (4) any antiparkinson drug in the absence of a diagnostic code for PD.

Results For patients with no previous antipsychotic use, lithium monotherapy was associated with an increased incidence of dopaminergic drug use (adjusted HR: 1.87; 95% CI: 1.06–3.30) and an increased incidence of antiparkinson drug use or a PD diagnosis (adjusted HR: 1. 68; 95% CI: 1.13–2.48) compared with antidepressant monotherapy.