Follow the manufacturer’s directions to use and clean the oral syringe. These medicines all work well for ED. On 6 May , Pfizer , which manufactures Viagra, told the Associated Press they will begin selling the drug directly to people on its site. What side effects can this medication cause? Generic versions of this low-dose form of sildenafil have been available in the U. This medicine also works best when you take it an hour before sex on an empty stomach.Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in adult males* with . Interactions. 1. How it works. Sildenafil may be used to treat erectile dysfunction (ED or impotence) in men (Viagra brand) or pulmonary arterial hypertension in both men and . Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). In combination with sexual stimulation, sildenafil works by increasing .