Tadalafil can be synthesized starting from D – tryptophan methyl ester and piperonal via a Pictet—Spengler reaction. Who should not take Cialis? Do not take a double dose or more than one dose per day to make up for a missed one. Tell your healthcare provider that you take Cialis. If you drink a large amount of alcohol more than five glasses of wine or five shots of whiskey while you are taking tadalafil you are more likely to experience certain side effects of tadalafil such as dizziness, headache, fast heartbeat, and low blood pressure. Comparison with actions of other PDE5 inhibitors[ edit ] Sildenafil and vardenafil inhibit PDE6, an enzyme found in the eye, more than tadalafil.Tadalafil (Cialis) is taken by mouth either as needed before sexual activity or once daily for erectile dysfunction (ED).It’s also taken once daily to treat symptoms from an enlarged prostate (benign prostatic hyperplasia, or BPH).Tadalafil (Cialis) is available both as brand-name and generic tablets. Common side effects of this medication include . Dosage range: mg to 5 mg. Frequency: once daily, regardless of the timing of sexual activity. Cialis’s recommended dosage when it’s taken as needed for ED is as follows. Dosage range: 5 mg to 20 mg. Frequency: one dose at least 30 minutes before sexual activity, with a maximum of one dose per day*. 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.