Ask your pharmacist for a list of the ingredients. If you are taking tadalafil for erectile dysfunction on a regular schedule, take the missed dose as soon as you remember it. This is a serious condition that requires immediate medical attention. It’s available in 50 mg, mg, and mg tablets. Patients should seek prompt medical attention if their erection lasts longer than four hours. Take tadalafil at around the same time every day.How can I buy tadalafil? You need a prescription from a doctor to buy tadalafil. You can buy it from a store-based pharmacy or reputable online pharmacy with a prescription. Some people buy tadalafil online without a prescription. This isn’t a good idea, as you can’t be sure whether these pills contain the medicine or are counterfeit. 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 . 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.