Vardenafil usually works for 4 to 5 hours. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Viagra vs. Natural Viagra alternatives may help address some of the underlying causes of erectile dysfunction, such as poor blood circulation or hormonal imbalances. Stop taking VIAGRA and call your healthcare provider right away if you have any sudden vision loss sudden hearing decrease or hearing loss.Is there an over-the-counter Viagra? Viagra is only available with a prescription in the United States, Canada, and most other countries. Viagra is sold under the generic name . As needed for ED: 5 to 20 mg by mouth as a one-time dose, with a maximum of one dose in 24 hours. Effects may last up to 36 hours. Daily dosing for ED: or 5 mg by mouth daily. For daily dosing, the maximum dose is 5 mg per day. The medication should be taken once daily at about the same time every day to maintain a consistent level of. Tadalafil (used in Cialis, Cialis Daily, and generic Tadalafil) – often known as the ‘weekend pill’, tadalafil medications get to work in about 30 mins and can last for up to 36 hours. Vardenafil (used in Levitra and generic Vardenafil) – similar to Viagra, vardenafil medications start after about 30 mins and last hours, but they.