Prolonged erections can be dangerous. Comparison with actions of other PDE5 inhibitors[ edit ] Sildenafil and vardenafil inhibit PDE6, an enzyme found in the eye, more than tadalafil. Tadalafil can be synthesized starting from D – tryptophan methyl ester and piperonal via a Pictet—Spengler reaction. It can also interact with many medicines, particularly nitrates used in some types of heart disease and blood pressure medicines. Persons surnamed “Cialis” objected to Eli Lilly and Company’s so naming the drug, but the company has maintained that the drug’s trade name is unrelated to the surname. Symptoms may include sudden urges to urinate urgency , difficulty in starting urination hesitancy , a weak urine stream, and more frequent urination — especially at night. If you take nitrates in any form, or are on treatment for pulmonary hypertension , you should not take tadalafil.quality Usually, generic drugs aren’t available until the expiration of the brand name’s patent. Eli Lilly and Company’s patent for Cialis expired in , opening the market to generic. Tadalafil (Cialis) is available both as brand-name and generic tablets. Common side effects of this medication include headache and indigestion. Tadalafil (Cialis) does interact with some medications, such as heart and blood pressure medications, and taking them together could lead to very low blood pressure and dizziness. 4 ways to save on Cialis. Here are four tips to help you maximize your savings on tadalafil. 1. Check your insurance coverage. Since Cialis is available as a generic, many insurance plans now cover it (to varying degrees). Generally, Medicare does not cover Cialis, since it’s not considered medically necessary.