Tadalafil is one of the more popular erectile dysfunction (ED) medications on the market and is most commonly associated with the brand name Cialis. Cialis is very similar to the popular ED medication Viagra with the biggest difference being the drug's active life. Cialis will produce erections for 36-48 hours from one single dose where Viagra is limited to 4-6 hours from one single dose. Cialis is also prescribed for the treatment of BPH (Benign Prostatic Hyperplasia), which refers to an enlarged prostate that results in difficulty or frequent urination.