Tadalafil belongs to a group of medicines called phosphodiesterase 5 PDE5 inhibitors. Tadalafil is sometimes taken as needed, usually at least 30 minutes before sexual activity and not more often than once every 24 hours. Remember, when in doubt, always consult with a healthcare professional. Patients who have a condition called “left ventricular outlet obstruction” from valvular problems or heart muscle enlargement may get side effects such as fainting or light-headedness. Be sure to mention any of the following: alpha blockers such as alfuzosin Uroxatral , doxazosin Cardura , dutasteride Avodart, in Jalyn , prazosin Minipress , silodosin Rapaflo , tamsulosin Flomax, in Jalyn , and terazosin; amiodarone Cordarone, Pacerone ; certain antifungals such as fluconazole Diflucan , griseofulvin Grifulvin, Gris-PEG , itraconazole Onmel, Sporanox , ketoconazole Extina, Ketozole, Nizoral, Xolegel , and voriconazole Vfend ; aprepitant Emend ; bosentan Tracleer ; carbamazepine Carbatrol, Epitol, Tegretol, Teril, others ; clarithromycin Biaxin, in Prevpac ; diltiazem Cardizem, Cartia,Tiazac, others ; efavirenz Sustiva, in Atripla ; erythromycin E. You can avoid potentially awkward encounters at a physical store. After taking a single tablet, some of the active ingredient of Cialis remains in your body for more than 2 days.Cialis (tadalafil) is a member of the impotence agents drug class and is commonly used for Benign Prostatic Hyperplasia, and Erectile Dysfunction. The cost for Cialis oral tablet mg is around $ for a supply of 30 tablets, depending on the pharmacy you visit. Quoted prices are for cash-paying customers and are not valid with insurance. Tadalafil is a medicine used to treat erectile dysfunction (ED, also called impotence) and problems with urination caused by an enlarged prostate (benign prostatic hypertrophy or BPH). It is sometimes known by its generic name tadalafil, and sometimes known by its trade name, Cialis. There are also other brands of this medicine available. The most commonly reported side effects in patients treated with Cialis during the testing of the product were: headache. indigestion. back pain. muscle pain. flushing. stuffy nose. Patients who.