However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Cialis will be available as oral tablets in 5mg, 10mg and 20mg strengths. Tadalafil does not prevent pregnancy or the spread of sexually transmitted diseases such as human immunodeficiency virus HIV. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. CIALIS can cause your blood pressure to drop suddenly to an unsafe level if it is taken with any nitrate medication. Your doctor will discuss the best treatment plan for you. If you have an erection that lasts for more than 4 hours, you should go to the nearest hospital emergency department.Tadalafil 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). It is sometimes known by its generic name tadalafil, and sometimes known by its trade name, Cialis. There are also other brands of this medicine available.  · One dose of Cialis can help improve erectile function for up to 36 hours. In comparison, Viagra’s effects can last up to 4 hours. My doctor prescribed 10 mg of Cialis for occasional use to. Tadalafil (Cialis) is taken by mouth either as needed before sexual activity or once daily for erectile dysfunction (ED).It’s also taken once daily to treat symptoms from an enlarged prostate (benign prostatic hyperplasia, or BPH).Tadalafil (Cialis) is available both as brand-name and generic tablets. Common side effects of this medication include .