Summary Cialis and Viagra are both pills for treating erectile dysfunction. When oral medications might not be safe Check with your health care team before you take any medicine for erectile dysfunction. This medicine also works best when you take it an hour before sex on an empty stomach. Severe liver disease. Its effects might last longer if you have mild to moderate ED.Cons can cause headaches and muscle aches must be swallowed whole can cause indigestion can make you appear flushed not available over-the-counter (OTC) . (1) One difference is that tadalafil (Cialis) is approved to treat both ED and BPH whereas sildenafil (Viagra) can only be used for ED. (2) Another difference is that . Differences Oral medications are a simple and effective way to treat erectile dysfunction (ED). The most common erectile dysfunction pill is Viagra, and the next most .