There is also the option to take Cialis as needed. Medicines that block an enzyme called CYP3A4. If you are a Mayo Clinic patient, this could include protected health information. Kidney disease that needs to be treated with dialysis. If so, how much?Generic Viagra (sildenafil) is available as a , , , and milligram (mg) pill and in liquid form. It’s meant to be taken as needed — about an hour before sex — but shouldn’t be. These are a few of the main differences between Cialis and Levitra: Dosage: Cialis is taken daily or as needed 30 minutes before sexual activity. Levitra is taken as needed at least 1 hour before. Oral medications are a successful erectile dysfunction treatment for many men. They include: Sildenafil (Viagra) Tadalafil (Adcirca, Cialis) Vardenafil (Levitra, Staxyn) Avanafil (Stendra) All four medications enhance the effects of nitric oxide — a natural chemical your body produces that relaxes muscles in the penis.