Pearlman says. Viagra can be taken as long as four hours or as little as 30 minutes before sex. There are two different ways to take tadalafil, either daily or on an as needed basis. No side effects were reported in sexual partners. How should this medicine be used? Tadalafil works for these conditions by promoting muscle relaxation, which improves blood flow in PAH and urinary flow in BPH. It might be a while before MED is available at your local pharmacy. · But on average, its effects start to lessen 2 to 3 hours after you take a dose. The typical dose for once-daily Cialis for ED is milligrams (mg) to 5 mg. When used as needed for ED, the usual. 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. 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 prostate) which include difficulty urinating (hesitation, dribbling, weak stream, and incomplete bladder emptying), painful urination, and urinary frequency and urgency in adult men.