Oral medicines for ED usually work well and cause few side effects. Its effects often last for 4 to 5 hours. How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup. As with sildenafil, a high-fat meal or alcohol keep the body from absorbing it as quickly. The most common side effects of VIAGRA: headache; flushing; upset stomach; abnormal vision, such as changes in color vision such as having a blue color tinge and blurred vision; stuffy or runny nose; back pain; muscle pain; nausea; dizziness; rash. They include dutasteride Avodart, Jalyn and finasteride Propecia, Proscar. You are encouraged to report adverse events related to Viatris products by calling U.Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles . Here are five things to know about the new topical gel and how it can help if you’re struggling to get an erection: 1. It Targets the Problem and Works Quickly. Being a . In the United States, sildenafil for ED or PH requires a prescription. The United Kingdom allows for over-the-counter (OTC) sales of the drug, in part to discourage the market for .