Do not mix the liquid with other medications or add anything to flavor the medication. If you experience chest pain, dizziness, or nausea during sex, seek immediate medical help. Do not stop taking sildenafil without talking to your doctor. This means that both the rate and extent of absorption are the same for both products, and therefore they should have the same effect. This medication is taken with or without food an hour before sex. When choosing one, tell your doctor or other health care professional what your preferences are, such as cost, ease of use, how long the drug’s effects last and side effects.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. Why is this medication prescribed? Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. 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 ED. With ED, you.