By controlling the enzyme, tadalafil helps to maintain an erection after the penis is stroked by increasing blood flow to the penis. Take all of the tablets for your daily dose at one time each day; do not divide the tablets to take as separate doses. Follow your doctor’s directions carefully, and ask your doctor or pharmacist to explain any part you do not understand. Read more on male sexual health on the Sexual Health Australia site. You should only be treated with one of these products at a time. John’s wort.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 .  · The typical dose for once-daily Cialis for ED is milligrams (mg) to 5 mg. When used as needed for ED, the usual Cialis dose is 10 mg (with a maximum daily dose of 20 mg). The typical dose of. Cialis is a brand (trade) name for tadalafil which may be used to treat erectile dysfunction (ED) and benign prostatic hyperplasia (BPH). Cialis (tadalafil) works by blocking the action of an enzyme known as cGMP-specific phosphodiesterase type-5 (PDE-5). This enzyme breaks down cGMP, a substance that induces smooth muscles to relax.