The effects of add-on prolonged-release melatonin ( PRM ) ( 2 mg ) to standard therapy on cognitive functioning and sleep were investigated in 80 patients ( men [ 50.7 % ] , women [ 49.3 % ] , average age 75.3 years [ range , 52-85 years ] ) diagnosed with mild to moderate AD , with and without insomnia comorbidity , and receiving standard therapy ( acetylcholinesterase inhibitors with or without memantine ) .