Objective. Many patients with chronic disease use alternative therapies. Our objective was to investigate complications resulting from the use of Chinese herbal medications containing undeclared prescription drugs, and to analyze these pills. Methods. Medical records of 5 patients with complications were reviewed. Pills from symptomatic and asymptomatic individuals were analyzed for possible content of undeclared prescription drugs. Results. All pills analyzed contained mefenamic acid and diazepam. Complications related to the presence of these substances included, among others, massive gastrointestinal bleeding. Conclusion. Chinese herbal medications may contain undeclared prescription drugs including nonsteroidal antiinflammatory drugs and benzodiazepines.