An overwhelming surge of information regarding preparedness for postvaccination side effects had caused widespread confusion approximately since April 2021, when the coronavirus disease 2019 (COVID-19) vaccination had started for the general population in Japan. Notably, this resulted in a remarkably increased shortage of OTC acetaminophen formulations. The aim of this study was to elucidate the actual responses of the public in such an environment, how individuals acquired and understood information related to the management of postvaccination side effects, and how they obtained and used antipyretic analgesics before and after COVID-19 vaccination. We conducted a web-based survey in January 2022, targeting 400 individuals aged ≥20 years, who had received two COVID-19 vaccine doses, and excluded qualified professionals such as physicians and pharmacists. The results revealed that 67% of the respondents had obtained antipyretic analgesics in anticipation of adverse effects after vaccination, whereas 38% had taken these medicines before and/or after the second vaccination. Possible misappropriation of medicines from others, preventive administration, and lack of dosage and administration confirmation are the problems identified in medication acquisition and usage. Additionally, avoidance of antipyretic analgesics based on information without scientific evidence was observed. This study revealed no small amount of inappropriate use of medicines in situations, such as the COVID-19 pandemic, where there is an infodemic of mixed-quality information. Pharmacists, as experts in medication, should play a crucial role in promoting appropriate medication usage by consistently staying updated with the latest scientific evidence and proactively supporting OTC drug selection and counseling medication.