The first document guaranteed sole production and sale of the substance until , while the second gave Pfizer the exclusive use to treating erectile dysfunction with sildenafil until It is thought that this reduced sales over the Internet and was safer as males could be referred for medical advice if appropriate. If you prefer, you may contact the U. This development was credited largely “due to the introduction of generic products. Numerous sites on the Internet offer Viagra for sale after an “online consultation”, often a simple questionnaire. This patent was published in and expired in The decision, Teva Canada Ltd.It’s a prescription drug that’s used in adult males* with ED. With ED, you have trouble getting or keeping an erection. Viagra treats ED by increasing the amount . Brand: Viagra. Form: oral tablet; Strengths: 25 mg, 50 mg, mg; Adult dosage (ages 18–64 years) Always carry the original prescription-labeled container .