Side effects that may occur while taking this medicine (impotence - Sildenafil citrate) include headache, flushing, stomach upset, heartburn, nasal stuffiness, diarrhea, dizziness, or lightheadedness.
Vision changes such as increased sensitivity to light, blurred vision, or impaired blue/green color discrimination may also occur. If these continue or are bothersome, check with your doctor or pharmacist.