This medicine is available only with your doctor’s prescription. Recent heart or blood vessel problems. An erection will not occur just by taking a pill. When the blood vessel muscle cells relax, this expands the vessel and increases blood flow; this effect is referred to as vasodilation. Both medications are generic now and can be found at discounted rates, making them more accessible to the public than ever before. Viagra vs. · Descriptions. Tadalafil is used to treat men who have erectile dysfunction (also called sexual impotence). Tadalafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where . Cialis is only available by prescription in the United States. Viagra: Additionally, a study from Trusted Source. found that combining L-arginine and sildenafil (Viagra) worked better for. Brand Cialis. Generic Tadalafil. No data.. Form. Bottle. Box. Disp Pack. Tablet. No data.. Dosage. mg. 5mg. 10mg. 20mg. No data.. Quantity. 5. 6. No data.