Sildenafil may cause side effects. Do not start these medications while taking sildenafil without discussing it with your healthcare provider. Generic versions of sildenafil, vardenafil and tadalafil are available. Common ones include: Flushing of the skin. You can take sildenafil with or without food. The body takes longer to absorb it after a high-fat meal or alcohol.Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. Viagra is approved for this use . FAQs 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 you take Viagra. . They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction (ED). Oral medicines for ED usually work well and cause few side .