Thanks for your question. Tadafil, popularly known as Cialis is a drug commonly used to treat erectile dysfunction. Cialis 5 mg is a tablet you can take on a daily basis regardless of whether you are going to have sexual intercourse or not. It is advised to take it at a regular time, every day. On the other hand, Cialis 20mg is an on demand drug, which is recommended about 30 minutes prior to sexual intercourse. It is your doctor who has to decide which one is suitable for you. Anyway it is not advised to take both of these tablets together. I think your doubt is cleared now. Take care.