At 4 and 8 weeks of medication and 1 month after withdrawal , the IIEF-5 scores were improved in both the on-time and on-demand groups , even more significantly in the former than in the latter at 8 weeks of treatment ( 21.6 + / - 2.9 vs 18.5 + / - 1.7 ) and 1 month after withdrawal ( 20.9 + / - 2.1 vs 17.9 + / - 2.3 ) ( P < 0.05 ) .