Two of these studies used fixed doses patients allocated to 25, 50 or mg and two studies were flexible patients started on 25 mg and could be moved to 50 or mg depending on their response. If it is not treated right away, priapism can permanently damage your penis sudden vision loss in one or both eyes. How does Viagra work? For more information about treatment with Viagra, read the package leaflet also part of the EPAR or contact your doctor or pharmacist. The logo is clickable and will appear on the sites of all online medicine retailers in the EU that are registered with their national regulatory authority.The short answer is yes; you can take Viagra or its generic form, sildenafil, every test1.rur you need to or should, depends. Since each person is different, you should consult with a doctor. 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.  · 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. 4. Contraindications.