It is usually administered by an injection, patch, or oral medication. When taken at the correct time and paired with sexual stimulation, the erection lasts long enough for successful intercourse. This increase in blood flow results in a firmer, longer-lasting erection. Popular ED medications found online include: Viagra sildenafil : As the first FDA-approved PDE5 inhibitor for ED, sildenafil is taken 30 minutes to four hours before sexual intercourse to help achieve and maintain an erection. Some services offer a subscription option where they’ll send your medications every month at a discount. If approved, the provider will issue a prescription.Oral medicines for ED usually work well and cause few side effects. The . Medications Prescribed: Viagra, Cialis, Cialis Daily, Levitra, tadalafil, .