This medicine also works best when you take it an hour before sex on an empty stomach. Often, these are prescribed for chest pain called angina. Its effects often last for 4 to 5 hours. If you prefer, you may contact the U. The information provided is for educational purposes only and is not intended to replace discussions with a healthcare provider.Viagra is available as the generic drug sildenafil. A generic drug is considered as safe and effective as the original drug. And generics tend to cost less than brand-name drugs. Learn More IF YOU CHOOSE BRAND-NAME VIAGRA, MAKE SURE YOU GET THE BRAND NAME Your prescription may have been filled with a generic version instead of . generic Revatio and Viagra Used for Pulmonary Hypertension and Erectile Dysfunction MORE expand_more Check your prescription Prescription 20mg sildenafil (30 tablets) .