Oral ED medicines might not work or might be dangerous if you also take any of the following: Nitrate medicines. You can take sildenafil with or without food. They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction ED. 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. Before taking sildenafil, tell your doctor and pharmacist if you are allergic to sildenafil, any other medications, or any of the ingredients in sildenafil tablet or suspension. Brand names Why is this medication prescribed? The body takes longer to absorb it after a high-fat meal or alcohol.Viagra costs around $60–$70 per tablet. Generic sildenafil can range from $2–$18 per pill.  · Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where this enzyme works. According to price-comparison site , generic Revatio will cost you as little as $ per pill, depending on where you fill your prescription. That’s compared with more than $50 per.