Follow your doctor’s orders or the directions on the label. Do not double doses. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines. Patients should seek prompt medical attention if their erection lasts longer than four hours. Although not all of these side effects may occur, if they do occur they may need medical attention.Generic tadalafil has been available since and has proven to be just as effective and safe as the brand name. The drug is available in low daily doses that keep the medication in your system. Cialis (tadalafil) is a type of PDE5 inhibitor that the Food and Drug Administration approved in Like other PDE5 inhibitors, it increases blood flow to the penis. There are two different ways to take Cialis: as needed or daily.