Cialis is also highly effective in reducing the symptoms of BPH. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. In trials of the drug, individuals taking Cialis saw a significant reduction in the frequency and urgency of urination and improved urine flow. Tadalafil can be synthesized starting from D – tryptophan methyl ester and piperonal via a Pictet—Spengler reaction. Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Without physical action to the penis, such as that occurring during sexual intercourse, tadalafil will not work to cause an erection. To provide you with the most relevant and helpful information, and understand which information is beneficial, we may combine your email and site usage information with other information we have about you.Was this helpful? How does Cialis work? Cialis works by increasing blood flow to the penis to help a person get and maintain an erection. It also blocks the PDE5 . Drug Summary What Is Cialis? Cialis (tadalafil) is a phosphodiesterase inhibitor used for treating impotence (erectile dysfunction, or ED). What Are Side Effects . Tadalafil (Cialis) is used to treat erectile dysfunction (ED, impotence; inability to get or keep an erection), and the symptoms of benign prostatic hyperplasia (BPH; an enlarged .