They include dutasteride Avodart, Jalyn and finasteride Propecia, Proscar. Medicines that block an enzyme called CYP3A4. How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup. Oral ED medicines might not work or might be dangerous if you also take any of the following: Nitrate medicines. These medicines are called PDE5 inhibitors.Is there an over-the-counter Viagra? Viagra is only available with a prescription in the United States, Canada, and most other countries. Viagra is sold under . If you do buy medicines over the internet: Check to see if an online pharmacy is legitimate. Never order medicines from an online pharmacy that doesn’t . 1. It Targets the Problem and Works Quickly. Being a topical means MED targets your penis directly and offers a “quick onset of action,” Dr. Pearlman Missing: walgreens.