More serious side effects may include a drop in blood pressure or an erection that lasts longer than four hours. 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? Those who don’t feel comfortable discussing ED with an in-person provider or lack time to visit a doctor’s office may find online ED prescriptions beneficial. Still other online pharmacies specialize in medications for only a select few health concerns or conditions. Yes, ED pills can cause side effects.Q&A 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 . Sildenafil Switch to brand medication info_outlined Used for Erectile Dysfunction MORE expand_more Check your prescription Prescription mg sildenafil (30 tablets) edit . Typical dosing for Sildenafil (Viagra) The typical dose is to take 50 mg of sildenafil (Viagra) by mouth, about 1 hour before sex, as needed. The maximum recommended dose is .