Cialis (tadalafil) is a prescription medicine specially designed for men suffering from impotence and unable to have sex therefore. It works by stimulating blood flow to the tissue of the penis therefore providing for a stable erection. In case of taking any nitrate-based drugs, such as isosorbide dinitrate, nitroglycerin or isosorbide mononitrate, you must not take Cialis, as a dangerous and possibly lethal reaction can occur. Do not take Cialis even if you finished taking such a medicine. Talk to your doctor about a period of time after which it is safe to take this medication. In case your health care provider told you to abstain from having sex because of safety concerns - you are not supposed to be taking Cialis and having sex. If you do this anyway, make sure you report to your doctor any of the following symptoms that may occur during the intercourse: nausea, dizziness, numbness or tingling in your jaw, neck, chest or arms, or chest pain, as these may be serious side effects that indicate you need to stop the treatment. Memory problems, back pain, muscle pain, stuffy nose, diarrhea, upset stomach, and headache are some of the side effects you may experience that are not supposed to last for too long anyway.