Social media has become an important source of health information and increasingly influences how individuals interpret symptoms, seek healthcare, evaluate treatment options, and make medical decisions. Although social media can improve access to health education, patient engagement, and peer support, it also facilitates the rapid dissemination of misinformation and unverified medical claims. The impact of social media on medical decision-making is influenced by health literacy, digital literacy, perceived source credibility, emotional responses, social influence, and previous healthcare experiences. Evidence indicates that reliable online health information can support informed decision-making and patient–provider communication, whereas misleading content may contribute to self-diagnosis, treatment refusal, inappropriate self-medication, delayed healthcare seeking, and vaccine hesitancy. This review summarizes the potential benefits and risks of social media health information and discusses the role of digital health literacy and healthcare professionals in promoting evidence-based decision-making.