Sildenafil vs vardenafil try not to eat grapefruit or drink grapefruit juice while you are being treated with Sildenafil. Many people using this medicine do not have serious side effects. It is preferable not to use Cialis with grapefruit juice, alcoholic beverages, tobacco. If you smoke tobacco and take Cialis concomitantly this may lead to a condition called NAION (sudden optic nerve-related vision loss). Inform your doctor before to take. Cialis if you have abnormal penis, including curved penis and birth defects of the penis, had coronary artery disease, arrhythmia, angina, heart attack or heart failure, hypo- or hypertension, bleeding, stomach ulcers, diabetes, hyperlipidemia (excess of lipids in the blood), sickle-cell anaemia, liver or kidney failure in history.