The rapid growth of the digital health market, estimated to reach over USD 900bn by 2032, has created a number of important data privacy, interoperability and patient trust issues. Blockchain, which is decentralized, immutable, and transparent, offers a potential solution for these problems. This review discusses blockchain as a networked database to build mobile-based digital health systems and provides an analysis of security management to manage security and trust among stakeholders. It reviews significant use cases in Electronic Health Records (EHRs), clinical trials, health data exchange, pharmaceutical supply chain, insurance claims, and patient consent management. Real-world use cases such as the Estonia eHealth system, the UAE’s blockchain health strategy, IBM Watson Health pilots and WHO’s MiPasa platform show global interest in the technology and the varied applications that emanate from it. However, the review also shows significant challenges, including scalability, data storage capacity, energy consumption, and regulatory fragmentation. Ethical issues, particularly around immutable data and the right to be forgotten, are also complicating adoption. Future research areas include cross-integrating blockchain with AI, IoT, federated learning, and establishing global standards for the blockchain-based health systems. The review ends on pursuing cross-disciplinary synergies, regulatory alignment and ethical protections to fully utilize the disruptive potential of blockchain in digital healthcare.