INS and Parkinson disease: Additionally, among these studies, one study researched the effect of galanthamine on verbal fluency in patients with PDD [33], one study researched the effect of intranasal insulin administration on letter fluency in PD patients [34], one study researched the effect of statin on verbal fluency in PD patients [21], but data necessary for NMA could not be extracted or calculated from these three studies; therefore, these three studies were excluded.