Cialis is not recommended for people taking any form of nitroglycerin because the combination may lower blood pressure to an unsafe level. Some people buy tadalafil online without a prescription. Cialis is also highly effective in reducing the symptoms of BPH. Comparison with actions of other PDE5 inhibitors[ edit ] Sildenafil and vardenafil inhibit PDE6, an enzyme found in the eye, more than tadalafil. Furthermore, the longer half-life is the basis for tadalafil’s daily therapeutic use in treating pulmonary arterial hypertension. It belongs to the drug class known as PDE5 inhibitors. In trials of the drug, individuals taking Cialis saw a significant reduction in the frequency and urgency of urination and improved urine flow.Cialis (tadalafil) is a brand-name oral tablet that’s prescribed for certain conditions, including erectile dysfunction. As with other drugs, Cialis can cause side effects, such as high blood.  · Drug Images Cialis (tadalafil) is prescribed to treat erectile dysfunction and symptoms of benign prostatic hyperplasia. It comes as a tablet that’s taken as needed or . 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.