As the researcher is wanting to compare the effects of two different drugs on the management of irritable bowel syndrome (IBS), he or she must administer the drugs to the participants. Because the researcher must intervene in the lives of the participants, an experimental study is most appropriate. Experimental study designs allow for the determination of "cause-and-effect" relationships, which is what this researcher is wanting to know (which drug causes better/worse outcomes on the management of IBS). Specifically, a double-blind placebo-controlled experimental design would be useful as placebo groups will help determine if either drug has actual effects, and the blindedness of the researchers and participants reduces biases (e.g. anticipation bias, favouritism, etc.).