What side effects can this medication cause? It continues to work for up to 4 hours, although its action is usually less after 2 hours. If you experience chest pain, dizziness, or nausea during sexual activity, call your doctor immediately and avoid sexual activity until your doctor tells you otherwise. Sildenafil is in a class of medications called phosphodiesterase PDE inhibitors. Do not mix the liquid with other medications or add anything to flavor the medication. · Descriptions. Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of . What to consider. Cost. Overdose. Ask your doctor. Q&A. Drug Images. What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that . Viagra (sildenafil) is a prescription drug that’s used to treat erectile dysfunction (ED). Viagra can cause side effects that range from mild to serious. .