Cialis (tadalafil) is a medicine classified as phosphodiesterase (PDE) inhibitor specially intended for patients diagnosed with erectile dysfunction and unable to hold their erection for long enough to have sex. You will need to take Cialis for as long as you want to get stable erection. However, make sure you never take more of it or use it more often than every 24 hours. An overdose of Cialis can produce the following symptoms: priapism, pain in the back, muscle pain, flushing, headache, stuffy or runny nose, indigestion, and heartburn. Although an overdose of this medicine is not expected to be dangerous, you will still need to report it to your local emergency center for your symptoms to be treated. Cialis is very well tolerated with just a few mild side effects possible, such as flushing, indigestion or heartburn, diarrhea, pain in the stomach, cough, headache, and muscle pain. Cialis can become less efficient or affect other drugs you are using if you didn't discuss them with your health care provider. The following meds are supposed to be discussed: isoniazid, alpha blockers, danazol, diltiazem, amiodarone, other erectile dysfunction treatments, rifampin, HIV protease inhibitors, erythromycin, clarithromycin, carbamazepine, rifabutin, antifungals, cimetidine, and medications for high blood pressure.