The following nonprescription or herbal products may interact with sildenafil: cimetidine Tagamet HB , St. You can take it up to 4 hours before you want to have sex. This medicine has been approved in the United States to treat premenopausal females who have low sexual desire. Do not start these medications while taking sildenafil without discussing it with your healthcare provider. What should I do if I forget a dose? If you are taking sildenafil to treat erectile dysfunction, you should know that it does not cure erectile dysfunction or increase sexual desire. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. · Hims is a telehealth company that provides both prescription and over-the-counter generic and brand-name medications. The brand focuses mainly on five medications, including Viagra, that have. About sildenafil (Viagra) Sildenafil is a medicine used to treat erection problems (erectile dysfunction). Sildenafil is also sometimes used to treat pulmonary hypertension (high blood pressure in the blood vessels that supply the lungs). If you have erection problems sildenafil works by temporarily increasing blood flow to your penis when. Key facts. Sildenafil (Viagra) is a medicine used to treat erectile dysfunction (ED, also called impotence). Sildenafil works by helping to relax the blood vessels in the penis, allowing more blood to flow in and cause an erection. You should take sildenafil about an hour before planned sexual activity, so it has time to work.