Cialis and Viagra Name brand versions of these drugs cost more. This leads to more blood flow to the penis, leading to stronger erections. Viagra can be taken as long as four hours or as little as 30 minutes before sex. However, the dosage can range from 25— mg. They have the same benefits and risks as their brand-name counterparts. You can take Viagra daily, but because the medication stays in your system for four to six hours, it will not be effective all day. Its effects might last longer if you have mild to moderate ED.Compare Cialis vs Sildenafil head-to-head with other drugs for uses, ratings, cost, side effects and interactions. Tadalafil (Cialis). This medication is taken with or without food an hour before sex. It works for up to 36 hours. You can take it in a small dose daily or in a larger . Pros • One of the first-choice medications for treating ED • Taken only when you need it • Can take it 30 minutes to 4 hours before sexual activity • Available as a lower-cost .