People with kidney or liver problems will need to either take a lower dose of Cialis or avoid the medication altogether, depending on the severity of the condition. Your doctor will probably tell you not to take tadalafil if you are taking nitrates. This process helps increase blood flow to the penis and achieve an erection. Dosages include 2. Cialis is approved in adults assigned male at birth; it is not approved for use in children or adolescents.Cialis and generic tadalafil are available with a prescription only. There is no OTC version, though there have been efforts in recent years to develop a . 1. What is Cialis used to treat? Cialis is approved for the treatment of men who experience difficulty having and maintaining an erection (impotence). 2. How does Cialis work? . Healthcare providers may also prescribe tadalafil to manage two other health conditions involving insufficient blood flow: pulmonary arterial hypertension (PAH) .