INS and Alzheimer disease: In non-AD patients: Sitagliptin vs. insulin vs. metformin: 0.95 ± 2.17 vs. 0.94 ± 1.89 vs. −2.50 ± 3.03, p = 0.02 In AD patients: only analysis comparing sitagliptin with metformin had sufficient power, with improved cognition observed in sitagliptin users p = 0.047