This medicine also works best when you take it an hour before sex on an empty stomach. They include dutasteride Avodart, Jalyn and finasteride Propecia, Proscar. It lasts 4 to 5 hours, or longer if you have mild to moderate ED. You can take this medicine with or without food 30 minutes before sex, depending on the dose. The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra.VIAGRA is available by prescription only in 25 mg, 50 mg, and mg tablets. Patients should always ask their doctors for medical advice about adverse events. You are . It’s available as a lower-cost generic. Reviewed by: Allison Barnes, PharmD. The list below does not include all possible drug interactions with Sildenafil (Viagra). Please note . Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in adult males* with .