Cialis reaches its maximum effectiveness two hours after you take it. Side Effects Along with its needed effects, a medicine may cause some unwanted effects. These medicines are called PDE5 inhibitors. Do not start these medications while taking sildenafil without discussing it with your healthcare provider. Different brands may not work the same way. However, eating food, particularly high-fat food, can reduce the effectiveness of Viagra. Which Lasts Longer?The average length of time Viagra lasts. On average, Viagra lasts between 2 and 3 hours before its effects start to diminish. Viagra can last up to 5 hours or longer depending on your dosage, your. Viagra (sildenafil) is a prescription drug that’s used to treat erectile dysfunction (ED). The drug comes as a tablet you’ll take by swallowing. It’s usually taken as needed about 1 hour. Hims offers generic Viagra starting at $3 per pill, and branded Viagra starting at $ per pill. To start with Hims, people must fill in an online questionnaire.