The response of a patient with an enteropathic disease to therapy, particularly a candidate therapy in a clinical trial setting, is assessed by detecting the ability of the patient to metabolize an orally administered CYP3A substrate. The CYP3A metabolism may be monitored in a variety of ways. Conveniently, the appearance of a metabolite of the CYP3A substrate is detected in a patient sample over a period of time following oral administration, e.g. in urine, plasma, breath, saliva, etc. The CYP3A substrate is optionally labeled, e.g. with an isotopic, fluorescent, etc. label.