As with sildenafil, a high-fat meal or alcohol keep the body from absorbing it as quickly. If you are taking sildenafil to treat PAH, you will probably take sildenafil three times a day with or without food. This medicine also works best when you take it an hour before sex on an empty stomach. What special dietary instructions should I follow? The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra.Note: Some pharmacies do not allow the savings card to be used for opioid drugs. How much does sildenafil citrate or viagra cost near you? Find the best sildenafil citrate or . The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. Sildenafil is a generic drug, which is an exact copy of the active drug in a brand-name medication. The generic is considered to be as safe and effective as the original drug. And generics tend to.