Viagra is an oral PDE-5 inhibitor approved by the FDA to treat erectile dysfunction (impotence), a common condition in men. Most men experience this unpleasant disease at some stage in their lives, it can be either caused by physical or psychological conditions. The active ingredient in this medicine is sildenafil citrate. According to a recent study, two out of three men who had erectile dysfunction reported that taking sildenafil tablets improved their erection. In most cases, the drug starts working within 30-40 minutes. The branded product comes in 3 dosages: 25mg, 50mg, 100mg. Generic manufacturers offer a rich selection of strengths: 120 mg, 130 mg, 150 mg, and 200 mg. Today, you can buy genuine Viagra online from various online pharmacies. But what is the best online pharmacy for Viagra? In this article, we will review these popular online drugstores: Walmart, CVS, Walgreens, and Trust Pharmacy. Where to buy Viagra online?