Generic versions of this low-dose form of sildenafil have been available in the U. United States Sildenafil is available as a generic drug in the United States, labeled for pulmonary arterial hypertension. Sildenafil usually should not be taken more than once every 24 hours. You should only be treated with one of these products at a time. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule.Sildenafil, sold under the brand name Viagra, among others, is a medication used to treat erectile dysfunction and pulmonary arterial hypertension. [4] [8] It is also sometimes used off-label for the treatment of certain symptoms in secondary Raynaud’s phenomenon. [9]. Viagra – Uses, Side Effects, and More Generic Name (S): sildenafil Uses Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED).  · a light-headed feeling, like you might pass out. Common sildenafil side effects may include: flushing (warmth, redness, or tingly feeling); headache, dizziness; heartburn, nausea, or upset stomach. abnormal vision (blurred vision, changes in color vision) runny or stuffy nose, nosebleeds; sleep problems (insomnia); or.