Talk with your healthcare provider about your sex life and desired use. Which Works Faster? Viagra generally only stays in your system for four to six hours. Talk with your healthcare provider about which might be best for you. For once-daily use, tadalafil is prescribed at a lower dosage of either 2. Want medication? Healthcare providers have experience talking about ED and providing treatment options without any judgment or shame.from around $18 for 30 tablets of 20 mg of generic tadalafil: from around $12 for 30 tablets of mg of generic sildenafil: Common side effects • headache • flushing • indigestion.  · Maximum dose: 20 mg orally three times a day. Injection: Initial dose: or 10 mg IV bolus three times a day. Comments: No greater efficacy was achieved with oral doses higher than the maximum recommended dose. A 10 mg injection dose is predicted to provide pharmacological effect equivalent to the 20 mg oral dose. There are 4 dosages of Cialis: mg (milligrams) 5mg. 10mg. 20mg. The mg and 5mg dosages are called Cialis daily, because you take them once a day. This way, you can always be ready to get and keep erections easier. The 10mg and 20mg dosages are called Cialis on demand because you don’t need to take them every day.