However, the dosage can range from 25— mg. Cialis can also interact with other medications, including nitrates and blood pressure medications. You need a prescription from a doctor to buy tadalafil. In pulmonary hypertension it works by relaxing blood vessels in the chest. You can buy it from a store-based pharmacy or reputable online pharmacy with a prescription. Cialis and Viagra are equally effective.A generic drug is an exact copy of the active drug in a brand-name medication and is considered just as safe and effective. Tadalafil (generic Cialis) may cost less than brand-name Cialis. 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. Brand-name and generic Cialis: The price for brand-name Cialis can be pretty high and might be outside of many people’s budgets. We included services that offer brand-name Cialis and generic.