Popular ED medications found online include: Viagra sildenafil : As the first FDA-approved PDE5 inhibitor for ED, sildenafil is taken 30 minutes to four hours before sexual intercourse to help achieve and maintain an erection. Most online providers require a picture of a valid ID, a selfie showing your face, and a recent blood pressure reading taken with a home blood pressure monitor or by a medical provider. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive. Online ED consultations offer privacy, convenience, and affordability while allowing you to quickly get the medications you need—the same day, with some services. Proper Use Use sildenafil exactly as directed by your doctor.VIAGRA is supplied as blue, film-coated, rounded-diamond-shaped tablets containing sildenafil citrate equivalent to 25 mg, 50 mg, or mg of sildenafil. Tablets are debossed with PFIZER on one side and VGR25, VGR50 or VGR on the other to indicate the dosage strengths. Close. VIAGRA can cause serious side effects. Rarely reported side effects include: an erection that will not go away (priapism). If you have an erection that lasts more than 4 hours, get medical help right away. If it is not treated right away, priapism can permanently damage your penis; sudden vision loss in one or both eyes. The average length of time Viagra lasts. On average, Viagra lasts between 2 and 3 hours before its effects start to diminish. Viagra can last up to 5 hours or longer depending on your dosage, your.