A manufacturer of a branded prescription drug typically uses traditional promotional tools to communicate with consumers (i.e., direct‐to‐consumer advertising) and physicians (i.e., detailing, sampling, and journal advertising). These promotions seek to enhance brand drug visibility and, eventually, increase brand sales. As medical communication norms generally dictate how healthcare information is communicated, the emergence of social media challenges such norms and potentially inflates (or deflates) the efficacy of pharmaceutical marketing communication. In such situations, a crucial research question revolves around how marketers will adjust their promotional strategies. In this study, the authors analyze the longitudinal data of 41 brand drugs from 7 therapeutic classes between 2007 and 2014. Through the lens of signaling theory, they empirically show that the volume and valence of social media posts can enhance or hinder the sales impacts of different promotional activities. Specifically, the volume and valence of social media posts have the potential to amplify the sales impact of detailing and direct‐to‐consumer advertising, while diminishing the effects of sampling and journal advertising. The volume and valence of brand drug mentions as well as consumer passion toward the brand drug display similar effects on the efficacy of pharmaceutical promotions. The findings shed new light on conventional pharmaceutical promotion practices in the presence of social media and provide novel implications for promotion mix management.