A clinical trial is an exceedingly important instrument in the assessment of treatment efficacy. With regard to clinical trials, the emphasis will be on methodological principles and on the clinical practice of therapeutic experiments. Furthermore, this course addresses the principles of studying the effects of drug treatments on the risks of unintended effects. The focus is on proper formulation of the research problem with respect to to clinical and regulatory relevance of the study results, and requirements for validity in non-experimental research.