When used with nitrates, Cialis and Viagra can produce a sudden drop in blood pressure levels that may cause dizziness, lightheadedness, fainting and serious cardiovascular events, such as heart attack or stroke. When taken at the correct time and paired with sexual stimulation, the erection lasts long enough for successful intercourse. If approved, the provider will issue a prescription. Other conditions that may disqualify you from an ED prescription include a history of stroke, kidney or liver disease, cancer, diabetes, or a bleeding disorder. Cialis is a brand-name prescription medication.Both Cialis and Levitra are FDA-approved to treat: Erectile dysfunction (ED) in adult males.* ED is the inability to achieve or sustain an erection firm enough for sexual activity. Cialis is a medication approved by the Food and Drug Administration (FDA) often used to treat erectile dysfunction (ED) and benign prostatic hyperplasia (BPH) in . 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*.