They are PDE5 inhibitors that allow for increased blood flow to the penis, leading to more frequent and harder erections. 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. There is also the option to take Cialis as needed. Talk with your healthcare provider about which might be best for you. You need a prescription from a doctor to buy tadalafil. John’s wort. Patients should seek prompt medical attention if their erection lasts longer than four hours.The recommended starting dose for Cialis intended for once daily use is mg, take at the same time each day, without regard to timing of sexual activity. This may be increased to 5mg/day based on need and tolerability. May be taken with or without food. Cialis is available as a generic, under the name tadalafil. 3. Roman sells the following versions of Cialis: Generic: available in tablets of 5, 10, and 20 milligrams (mg), starting from $11 Daily Generic: available in doses of and 5 mg at $8 Branded. Dosage. The dose of Cialis you need will depend on whether you’re taking it daily or as needed. Daily doses are often between and 5 milligrams (mg). The as-needed dose is usually 10 mg but can range from 5–20 mg. The typicaldose of Viagra is 50 mg. However, the dosage can range from 25– mg.