ED occurs more frequently in older men. The drug is approved for use in adults. Erectile dysfunction is a condition where the penis does not harden and expand when a man is sexually excited, or when he cannot keep an erection. Sorry something went wrong with your subscription Please, try again in a couple of minutes Retry. If you are taking tadalafil for erectile dysfunction, your doctor will probably start you on an average dose of tadalafil and increase or decrease your dose depending on your response to the medication. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine. Use only the brand of this medicine that your doctor prescribed.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). 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. 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.