This study investigated Vietnamese people’s behavior and future intention to purchase medicines and functional foods online and their associated factors. From March to May 2023, a Google Form questionnaire was distributed via social networks and online platforms. Convenience and snowballing sampling methods were employed to recruit 1,305 Vietnamese people. In the past year, 50.3% of participants purchased at least one kind of medicine and/or functional foods online (medicines: 27.6%, functional foods: 45.1%). Among 656 buyers, nearly a third bought these products more than three times and only 5.9% felt dissatisfied with their previous experiences. This purchasing behavior was more prevalent among females, those married, having higher education levels, usually shopping online, having longer time of Internet use per day, and seeking health information on the Internet (p < 0.001). In addition, 77.5% of participants intended to purchase these products online in the future and 61.2% would introduce this kind of online purchase to other people. The purchase intention was significantly associated with the participants’ previous experiences, area, contracting chronic diseases, and using the Internet for self-medication, while factors associated with the introducing intention included their education level, occupation, and previous experiences in online purchases (p < 0.001).