The same principles and the role of sildenafil, are relying on cGMP by inhibiting PDE-5 to increase the decomposition of NO in the vasodilator effect in that the ED patients regain erectile capacity. Tadalafil, the average onset time is 16 minutes. 2 hours after taking the peak plasma concentration, half-life of 18 to 48 hours, or even 5 days later, can still be measured in the plasma concentration of tadalafil. Clinical reports show after taking Cialis efficiency of 83%. Cialis compared to the advantage of side effects of sildenafil, long duration, can have a significant effect of 7 days.