The blue, oval, 13mm pill with "R 50" imprint is Sildenafil Citrate 50 mg, a prescription medication used to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH) by relaxing blood vessels to improve blood flow. It's a PDE5 inhibitor taken as needed before sexual activity, but never more than once daily, and requires medical consultation for proper use and to avoid serious side effects like vision loss or low blood pressure, especially if taking nitrates.