Sildenafil may cause side effects. Take sildenafil as needed before sexual activity. If you become pregnant while taking sildenafil, call your doctor. Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient. Follow the manufacturer’s directions to use and clean the oral syringe.Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in . · Proper Use. Drug information provided by: Merative, Micromedex ®. Use sildenafil exactly as directed by your doctor. Do not use more of it and do not use it more . 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. It’s a .