Your doctor will probably tell you not to take tadalafil if you are taking nitrates. A small number of patients taking Cialis also reported abnormal vision. Also tell your doctor if you or any of your family members have or have ever had an eye disease such as retinitis pigmentosa an inherited eye condition that causes loss of vision or if you have ever had sudden severe vision loss, especially if you were told that the vision loss was caused by a blockage of blood flow to the nerves that help you see. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. After taking a single tablet, some of the active ingredient of Cialis remains in your body for more than 2 days. Prolonged erections can be dangerous.Dosage range: mg to 5 mg. Frequency: once daily, regardless of the timing of sexual activity. Cialis’s recommended dosage when it’s taken as needed for ED is as follows. Dosage range: 5 mg to 20 mg. Frequency: one dose at least 30 minutes before sexual activity, with a maximum of one dose per day*. AdGet a Prescription for ED treatment, discreetly deliverED to your door. Tadalafil Brand names: Cialis, Adcirca. Tadalafil. Find out how tadalafil treats erectile dysfunction, pulmonary hypertension and benign prostate enlargement, and how to take it.