What is the difference between sildenafil and Viagra? Medically they are the same and work in the same manner. Viagra is Pfizer’s brand name for sildenafil. Sildenafil Citrate 100mg is the medicinal name for the active ingredient in both. Sildenafil and Viagra both come in packs of fourth and eight tablets in strengths of 25mg, 50mg, and 100mg. They are interchangeable.