How can I buy tadalafil? If you have an erection that lasts for more than 4 hours, you should go to the nearest hospital emergency department. If you need emergency medical care for a heart problem, it will be important for your health care provider to know when you last took Cialis. Your doctor will discuss the best treatment plan for you. The safety and effectiveness of Cialis when used with other treatments for impotence has not been studied. What alternatives can I use for erectile dysfunction? Cialis will be available by prescription only.What Are The Possible Side Effects Of Cialis? The most common side effects with Cialis are: headache, indigestion, back pain, muscle aches, flushing, and stuffy or runny nose. These side effects usually go away after a few hours. Men who get back pain and muscle aches usually get it 12 to 24 hours after taking Cialis. headache. indigestion. back pain. muscle pain. flushing. stuffy nose. Patients who get back pain and muscle aches usually get them 12 to 24 hours after taking Cialis and these usually go away by. Tadalafil (Cialis) is a medicine used to treat erectile dysfunction (ED, also called impotence) and problems with urination caused by an enlarged prostate (benign prostatic hypertrophy or BPH). Tadalafil works by helping to relax the blood vessels in the penis, allowing blood to flow into the penis, and causing an erection.