Its effects often last for 4 to 5 hours. Cialis reaches its maximum effectiveness two hours after you take it. Cialis and Viagra are equally effective. Levitra vardenafil : This medication is taken one hour before sex and can last up to 24 hours. This medication is taken with or without food an hour before sex. This allows an increase of blood flow into the penis.You need a prescription to get Cialis, which you can acquire through your doctor or telehealth sources. Online ordering can be a great alternative if you prefer the convenience and discretion. Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. This boosts blood flow and helps you get an erection from sexual activity. Differences Oral medications are a simple and effective way to treat erectile dysfunction (ED). The most common erectile dysfunction pill is Viagra, and the next most common is Cialis. Both medications are phosphodiesterase type 5 (PDE5) inhibitors that work by increasing blood flow to the penis.