Your doctor will recommend the dosage of Viagra that s right for you. Form and strengths (25 mg, 50 mg, 100 mg) Viagra comes as an oral tablet, in these strengths: 25 milligram (mg), 50 mg, and ivermectin-12mg.com Cialis works by enhancing the effects of one of the chemicals the body normally releases into the penis during sexual arousal. This allows an increase of blood flow into the penis. An erection is