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. This course addresses the principles of studying the effects of drug treatments on the risks of unintended effects. The accent is on proper formulation of the research problem with a view to clinical and regulatory relevance of the study results, and on requirements for validity in non-experimental research. The course program covers the principles of therapeutic research design, including design of study, design of data collection, design of data analysis, including some modelling techniques in the analysis to clinical trials, and the interpretation of its results. The program also covers the principles of drug risk assessment in the context of therapeutic research.