Viagra generally only stays in your system for four to six hours. Cialis stays in your system for up to 36 hours and may provide support for erections during that entire time. Effects of VIAGRA on Vision: At single oral doses of mg and mg, transient dose-related impairment of color discrimination was detected using the Farnsworth-Munsell hue test, with peak effects near the time of peak plasma levels. VIAGRA was evaluated primarily at doses of 25 mg, 50 mg and mg in 21 randomized, double-blind, placebo-controlled trials of up to 6 months in duration, using a variety of study designs fixed dose, titration, parallel, crossover. The pattern of responses was similar for the other principal question, the ability to achieve an erection sufficient for intercourse.AdGet a Prescription for ED treatment, discreetly deliverED to your test1.ruive Offers · How It Works · Get More Info4/5 ( reviews)Types: Finasteride · Shipping Policy · Tadalafil · Sildenafil. 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. Examples of Viagra’s more commonly reported side effects include: headache. flushing (temporary warmth, redness, or deepening of skin color) stuffy nose. indigestion (upset stomach) mild vision.