Severe liver disease. You may attempt sexual activity at any time between doses. You can see an in-person provider or speak with a doctor virtually. Tadalafil has been extensively studied for ED. People with heart conditions should never take ED medications without consulting a doctor. Tell your doctor if any of these symptoms are severe or do not go away: headache.Cialis lasts up to 36 hours in the body, while Viagra lasts 4–6 hours in the body. Both are taken 30 minutes before sex. Cialis can cause limb pain, while Viagra can cause vision change, rash. AdGet a Prescription for ED treatment, discreetly deliverED to your ive Offers · How It Works · Get More Info4/5 ( reviews)Types: Get Started · Tadalafil · Sildenafil. How Cialis Works. Tadalafil and other PDE5 inhibitors primarily work by inducing muscle relaxation. Tadalafil stops the breakdown of a chemical responsible for relaxing muscles. In ED and PAH, the drug targets muscle cells in blood vessels. When the blood vessel muscle cells relax, this expands the vessel and increases blood flow; this .