These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects. However, some states require a live video consultation. 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. Oral medicines for ED usually work well and cause few side effects. Never purchase ED medications from a site or service that doesn’t require a prescription and medical documentation. Its effects often last for 4 to 5 hours. Your doctor or other health care professional can recommend one for you based on these factors, other health conditions you have and any other medicines you take.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 . Generic Viagra (sildenafil) is an alternative to the branded Viagra drug that can be used for treating erectile dysfunction (ED). It’s now sold by many manufacturers, including online. from $7, for milliliters Oral Tablet 20 mg sildenafil oral tablet from $ for 10 tablets 25 mg sildenafil oral tablet from $ for 30 tablets 50 mg sildenafil oral .