A dose of 0. The Xanax XR may provide a more consistent and lower effective concentration, therefore resulting in a lower required dose with less side effects. Whether switching to Xanax XR is appropriate or not is a decision between the prescriber and the patient. Factors worth considering are dependency, tolerability of current medication and cost. For further information, please refer to the following links. What are the effects of taking Xanax and over-the-counter drugs, such as vitamin C, Caltrate, zinc, and Metamucil?