Purpose of Review <p>This review comprehensively analyzes the ecological impacts of antibiotics at environmental concentrations on microalgal communities, focusing on hormesis effects on cyanobacterial species. We discuss how these effects influence cyanobacterial growth, community succession, and the formation of harmful algal blooms (HABs), which are detrimental to aquatic ecosystems and human health.</p> Recent Findings <p>Antibiotics at environmental concentrations can stimulate cyanobacterial growth, leading to a hormesis effect characterized by biphasic dose-response curves. Such stimulation phenomenon has been observed to enhance photosynthetic capacity, increase the production of microcystins (MCs), and alter the gene expression and metabolic processes. Furthermore, the presence of antibiotics in the environment has been shown to selectively promote cyanobacterial proliferation over green algae and diatoms, potentially facilitating the outbreak of cyanobacterial blooms. The review also highlights the role of antibiotics in modulating the interactions between cyanobacteria and bacteria, as well as the impact on antibiotic resistance genes (ARGs) in aquatic systems.</p> Summary <p>Antibiotics at environmental concentrations shape the structure of microalgal communities and promote the proliferation of cyanobacteria, which contributes to the formation of harmful blooms. The hormesis effect induced by antibiotics at low concentrations warrants critical attention in the context of aquatic ecosystem health and cyanobacterial bloom control. Future research should prioritize long-term, realistic environmental exposure scenarios, focusing on mechanisms such as community dynamics, resistance gene transmission, adaptive responses of cyanobacteria, and the potential influence of antibiotic mixtures on blooms stability and toxin production.</p>