John’s wort. In , Pfizer scientists discovered that sildenafil, which also inhibits the PDE5 enzyme, caused penile erection in males participating in a clinical study of a heart medicine. Your doctor will probably tell you not to take tadalafil if you are taking street drugs containing nitrates. 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 sometimes taken as needed, usually at least 30 minutes before sexual activity and not more often than once every 24 hours.Tadalafil (Cialis) is used to treat erectile dysfunction (ED, impotence; inability to get or keep an erection), and the symptoms of benign prostatic hyperplasia (BPH; an enlarged prostate) which include difficulty urinating (hesitation, dribbling, weak stream, and incomplete bladder emptying), painful urination, and urinary frequency and urgency in adult men. Original Series. Fresh Food Fast; milligrams (mg), 5 mg, 10 mg, and 20 mg. Depending on the Brand-name and generic Cialis: The price for brand-name Cialis can be pretty high and might. Cialis (branded Tadalafil) Cialis is a reliable, branded ED treatment that lasts up to 36hrs. Can be taken with food. Works in 30mins, lasts up to 36hrs. Works for 80% of men. 10mg 20mg. 4 tablets. Out of stock. 8 tablets.