In recent years, general practice consultation has often been characterized as an argumentative activity. It has been argued that, guided by the ethical and legal principle of informed consent and the ideal standards of participatory and evidence-based medicine, doctors should provide argumentative support for their recommendations in order to encourage patients to actively take part in the treatment decision-making discussion. Thus far, however, it has remained unclear what causal effect general practitioners’ provision of argumentation may have on consultation outcomes, such as patients’ perceptions of their doctors’ decision-making style and credibility, their acceptance and recall of the medical advice, and subsequently their intention to adhere to the advice. In this study, therefore, the effect of general practitioners’ argumentative support for their treatment recommendations is studied experimentally using scripted video-vignettes. Moreover, rather than focusing merely on the presence of argumentation, the role of the pragma-dialectical reasonableness of general practitioners’ argumentation is also taken into account.