This paper hypothesizes that higher proficiency in the medium of instruction (MI) is a precondition for effective instructional communication (IC), with the latter being essential for higher cognitive processes, positive affects, and better performance in the learning environment. The reported study used questionnaires comprising open-ended questions to survey 341 content instructors who taught on 26 undergraduate programs with English as the MI (EMI) in a Saudi public university. Thematic analysis was used to analyze the resulting qualitative data, and the results reveal four themes. The first theme is the advantages of using the students' mother tongue (Arabic in this case) as an MI; the findings show that doing so is related to robust IC, with the latter leading to better cognition, positive affects, and stronger performance in the learning environment. The second theme is the advantages of using EMI, which can be classified into three main areas: more educational resources, better international research collaboration, and more international job opportunities. The third theme is the use of code-switching in EMI classes because of poor IC; instructors code-switch for three purposes: cognitive, affective, and performance. The fourth theme is suggestions from participants for how to improve IC in EMI programs: the findings recommend the use of IC theory and linguistic relativity to examine EMI programs; also, collaboration among IC researchers, cognitive linguists, and EMI researchers will help understand how the MI influences students' success; furthermore, policymakers must design curricula that consider the perspectives of content instructors and provide them with training to overcome several IC barriers in EMI programs.