Viagra (also known as sildenafil), Levitra (also known as vardenafil) and Cialis (also known as tadalafil) are all used in the treatment of erectile dysfunction. All three drugs block the actions of the same enzyme, called PDE5, so it would seem that all should work equally well. I am not aware of any direct comparison studies in the same patient population, so there are no studies to help identify if any one drug is better than the others. Although direct comparisons are difficult, there is likely to be a difference related to dosing. The maximum dose recommend for Viagra is 100 mg. The maximum dose of Levitra is 20 mg. The 20 mg dose of Levitra is about double the dose of 50 mg of Viagra. So, the difference in experience may simply be one of dose.
It is not uncommon for people to report that one drug in a class appears to work better than others. Although Viagra, Levitra, and Cialis all work essentially the same way, there are enough differences to account for variations in how well the drugs work in particular individuals. For example, there are additional forms of the PDE enzyme in the body. All three drugs block the different forms of the PDE enzymes to some degree but the drugs vary in how potently each blocks the specific PDE5 form.
