Because Viagra is it produced earlier then Levitra or Cialis

Cialis and Levitra. Ask your doctor.

Levitra, like Viagra or cialis work by relaxing or dilating the blood vessels to improve blood flow to the penis.

Vardnafil is the drug levitra. It's purpose is to cure erectile dysfunction, and works similar to Viagra.

Levitra and Cialis work the same way as Viagra, blocking the same enzyme. Though it's unlikely any one works better than Viagra overall, slight chemical differences mean that if one brand doesn't work for a patient, another one might.