•Participants read multiple documents with or without media multitasking.•Participants summarized main ideas of paragraphs or reread paragraphs.•Media multitasking negatively affected processing and comprehension.•Main idea summarization mitigated effects of multitasking on comprehension. Media multitasking refers to simultaneous engagement in two activities, or the act of switching between multiple activities, of which at least one is a media activity. Based on this definition, we had 134 Norwegian undergraduates read four partly conflicting documents on sun exposure and health on a computer in order to write a report on the issue, with half of the participants (randomly assigned) receiving and reading short, authentic social media messages on a smartphone while reading the documents, and the other half reading the documents without being sent any such messages. Further, we manipulated what participants did after reading each document paragraph, with half of the participants (randomly assigned) briefly summarizing the main idea of each paragraph in writing, and the other half just rereading each paragraph. Participants’ integrative processing (i.e., cross-text elaboration strategies) were assessed with a task-specific self-report measure immediately after reading all four documents, and their comprehension of the documents was assessed by analyzing their written reports in terms of their ability to elaborate and integrate information within and across the perspectives discussed in the documents. Results indicated that social media multitasking on a smartphone disturbed both the integrative processing and the integrated understanding of the documents, with main idea summarization mitigating or counteracting these negative effects of multitasking. However, when controlling for working memory, reading comprehension skills, and prior knowledge, integrative processing was not found to mediate the effect of multitasking on integrated understanding of the documents. Limitations of the present study and directions for future research are discussed.