For treatment of pulmonary arterial hypertension: Adults—40 milligrams mg two 20 mg tablets taken once a day. Ask your healthcare professional how you should dispose of any medicine you do not use. When using this medicine for erectile dysfunction, the ability to have sexual activity may be improved for up to 36 hours after taking the tablet. This medicine can cause serious side effects in patients with heart problems. It belongs to the drug class known as PDE5 inhibitors. What special precautions should I follow? What side effects can this medication cause?Tadalafil is the generic version of Cialis and is typically lower in cost. Share on Pinterest. Daily tadalafil: and 5: starting from around $8: Cialis: , 5, 10, and AdComplete the Online Consultation with our Doctor. Personalize Your Needs. If Appropriate, Get a Prescription for ED from RexMD®. Free Shipping Available. If you’re taking Cialis mg daily for ED versus 20 mg as needed before sexual activity, your cost may be different depending on how often you take the drug. Tadalafil (generic Cialis) may.