Aims: This research aimed to evaluate and examine various aspects of the evidence necessary for making well-informed health decisions, as well as the qualities of plain language summaries (PLSs) published by medical and non-medical organizations. The goal was to contribute to the comprehension of this topic through empirical research and offer valuable insights into the fields of health communication and evidence-based decision-making. Methods: We conducted two cross-sectional studies (questionnaire-based and methodological). We included different stakeholders in the healthcare system (researchers, healthcare workers, and consumers) and analyzed all PLSs from the latest versions of SRs published by Cochrane (medical), Campbell Collaboration, and the International Initiative for Impact Evaluation (non-medical). We assessed the stakeholders' comprehension of the hierarchy of evidence and conclusiveness, readability, and textual characteristics of the PLS. Results: Researchers were most capable of differentiating between study designs, while consumers and healthcare workers did not differentiate between observational studies, experimental studies, and SRs. Furthermore, medical PLSs were less conclusive and displayed lower readability than non-medical PLSs. Additionally, medical PLSs contained more words displaying emotions of disgust and fear, while non-medical PLSs displayed more positive emotions. Conclusions: Courses on basic research methodology should be required for lower-level learners and included in Continuing Medical Education for all stakeholders in the healthcare sector. Overall, our results may help PLS readers better understand and engage with the scientific information, which, in turn, improves their decision-making abilities and may have significant implications for the field.