Fifty million people around the world are currently affected by epilepsy. Fortunately, the disease responds to treatment 70% of the time, but many of the medications prescribed require multiple dosages per day. To ensure patient compliance, prevent adverse consequences due to missed dosing, and to enhance medicative convenience for the patient, Tegretol has engineered as extended-release pill, Tegretol-XR, which delivers carbamazepine at a nearly constant rate for a twelve hour time period. The design of these tablets involves a drug infused matrix surrounded by an insoluble shell, with a small orifice to allow drug release. When water diffuses through the orifice, the interior pill matrix saturates, and carbamazepine begins to elute out of the orifice until depletion, a process that is designed to take twelve hours. Using COMSOL, a Tegretol-XR tablet was modeled as a 2D rectangular, axisymmetrical slab. Researched diffusivity constants were found to precisely model the water and drug flow into and out of the pills. The diffusion of the drug is coupled with the concentration of water, and as the water infuses into the pill, the diffusivity of the drug is altered, ultimately leading to a sustained release of carbamazepine over the allotted twelve hours. Results from our model indicate that drug release closely follows ideal release kinetics and keeps an ample amount of drug in the bloodstream at all times. It was found that altering the orifice size by 5% resulted in changes of up to 16% in final average drug concentration, implicating that this is the most sensitive variable analyzed. Variables like water diffusivity were much less influential to the final solution. Our model of Tegretol-XR gives epileptic patients the option of taking only two pills a day, and thus, significantly lowers the risk of a missed dose.