 Probe compounds can be initially administered to subjects in the absence of suspected enzyme inhibitors or inducers and the parent drug or drug: metabolite ratios measured in plasma and urine to reflect enzyme activity. This assessment can then be repeated in the presence of a suspected inhibitor or inducer and comparisons can be made. In this manner, specific enzyme inhibitory or inductive effects can be elucidated, documented, and generalized to other similar substrates. In this study, by using the selected probe substrates alprazolam CYP3A4, dextromethorphan CYP2D6, tolbutamide TOL CYP2C9 and caffeine CYP1A2, we will assess the ability of MTSM to selectively alter one or more of the major drug metabolizing enzymes responsible for the metabolism of 80 of all therapeutically used drugs. 