Missed Dose If you miss a dose of this medicine, take it as soon as possible. What special precautions should I follow? Read and follow these instructions carefully. Sorry something went wrong with your subscription Please, try again in a couple of minutes Retry. Children—Use and dose must be determined by your doctor. The enlarged prostate interferes with the normal flow of urine from the bladder and urinary tract, resulting in lower urinary tract symptoms, such as trouble urinating.Tadalafil (Adcirca) is used to improve the ability to exercise in people with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the lungs, causing shortness of breath, dizziness, and tiredness). Tadalafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Cialis is a prescription medication containing the active ingredient tadalafil. Cialis belongs to a group of medications known as phosphodiesterase-5 (PDE-5) inhibitors. Healthcare providers commonly prescribe tadalafil to treat erectile dysfunction (ED). Can I Take 40 mg of Tadalafil (Cialis) for ED? Medically reviewed by Joseph Brito III, MD Here’s what to know about taking 40 mg of Cialis, why it could be bad for you, and other options.