The rising prevalence of infectious diseases and immune-related disorders underscores the need for effective and accessible therapeutic solutions. Herbal immunostimulants derived from medicinal plants offer promising alternatives, enhancing immune responses with lower toxicity and fewer side effects than synthetic drugs. This review explores the immunostimulatory potential of Morinda citrifolia, Echinacea purpurea, and Phyllanthus niruri, focusing on their bioactive compounds, mechanisms of action, and therapeutic relevance. These plants modulate innate and adaptive immune responses by activating macrophages, dendritic cells, and lymphocytes while regulating cytokine production to maintain immune homeostasis. Their immunomodulatory effects are linked to key signaling pathways, including NF-κB, MAPK, and JAK/STAT. In vitro and in vivo studies highlight their potential to strengthen immune responses and control inflammation, making them promising candidates for managing infectious and immune-related diseases. However, further research is needed to standardize formulations, determine optimal dosages, and validate safety and efficacy in clinical settings. Addressing these gaps will support the integration of herbal immunostimulants into evidence-based healthcare as sustainable and accessible immune-enhancing strategies.