It may be difficult to remain firm despite wanting to have sex. 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. Patients should always ask their doctors for medical advice about adverse events. Rogue pharmacies are not licensed to sell in the United States and put you at risk of counterfeit or tainted drugs How Many Online Pharmacies Are There? If you prefer, you may contact the U. An erection results from an increase in blood flow to the penis.Last updated: June 14, If you’re looking for a less costly Viagra, you might want to ask your doctor about sildenafil. It’s the active ingredient in both branded Viagra and the . Transfer your prescription for Sildenafil (Generic for Viagra, Oral Tablet) on Amazon Pharmacy. FREE SHIPPING for Prime members. SILDENAFIL (ERECTILE DYSFUNCTION) – ORAL. (sil-DEN-a-fil) COMMON BRAND NAME (S): Viagra. USES: Sildenafil is used to treat male sexual function problems .