Primary analysisMain studies – The efficacy of sildenafil 25, 50 and 100 mg was compared to placebo in the two fixed dose studies (studies 102, 364), while in the two placebo flexible dose studies, subjects started on a dose of 50 mg (study 103) or 25 mg (study 363) and were allowed to adjust the dose up or down based on efficacy and toleration. usa cialis Graded Risk (11).