Cialis is a phosphodiesterase inhibitor. It works by helping to increase blood flow into the penis during sexual stimulation. This helps you to achieve and maintain an erection.

Some medical conditions may interact with Cialis . Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:

* if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
* if you have allergies to medicines, foods, or other substances
* if you have a deformed penis (eg, Peyronie disease, cavernosal fibrosis), blood problems (eg, sickle cell anemia, leukemia, multiple myeloma), or any other condition that may increase the risk of a prolonged erection (priapism)
* if you have a history of certain eye problems (eg, retinitis pigmentosa, sudden vision loss, optic neuropathy, macular degeneration)
* if you have a history of liver or kidney problems, dialysis, high or low blood pressure, ulcers, bleeding problems, blood vessel problems, heart problems (eg, heart failure, irregular heartbeat, aortic stenosis, angina), or blood vessel problems
* if you have a history of heart attack, stroke, or life-threatening irregular heartbeat

Some MEDICINES MAY INTERACT with Cialis . Tell your health care provider if you are taking any other medicines, especially any of the following:

* Alpha-blockers (eg, doxazosin), medicines for high blood pressure, nitrates (eg, isosorbide, nitroglycerin), or nitroprusside because severe low blood pressure with dizziness, lightheadedness, and fainting may occur
* Azole antifungals (eg, itraconazole), HIV protease inhibitors (eg, ritonavir), macrolide antibiotics (eg, erythromycin), or telithromycin because they may increase the risk of Cialis ‘s side effects
* Rifampin because it may decrease Cialis ‘s effectiveness

This may not be a complete list of all interactions that may occur. Ask your health care provider if Cialis may interact with other medicines that you take. Check with your health care provider before you start, stop, or change the dose of any medicine.