Oral ED medicines might not work or might be dangerous if you also take any of the following: Nitrate medicines. Tadalafil Cialis. Generic versions of sildenafil, vardenafil and tadalafil are available. They will work for roughly 36 hours, allowing you to perform at your peak several times over a couple of days. As opposed to at least twice that on daily medicine. All of these Phosphodiesterase 5 inhibitors work in a similar way: the relaxation of the penile blood vessels to support expansion, which gives a stronger erection during arousal. Avanafil Stendra.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 . By Mayo Clinic Staff Medicines that you take by mouth are called oral medicines. They’re often the first line of treatment for trouble getting or keeping an . Compare Drugs Print Comparing Cialis vs Tadalafil Cialis (tadalafil) Tadalafil Prescription only Cialis is used to treat erectile dysfunction (ED) and to reduce symptoms of benign .