Deep eutectic solvents (DESs) have recently gained attention as promising tools for improving the stability and delivery of sensitive biomolecules in pharmaceutical formulations. Characterized by their tunable compositions, low toxicity, and environmental compatibility, DESs present a compelling alternative to conventional solvents in drug development. Their ability to mitigate challenges such as poor solubility and limited shelf life makes them particularly attractive for biopharmaceutical applications. Thus, this chapter examines the physicochemical interactions between DESs and therapeutic biomolecules, focusing on how solvent composition, concentration, and ambient conditions affect molecular stability and delivery performance. We also assess the practical advantages and potential drawbacks of incorporating DESs into medical formulations, with attention to regulatory and formulation challenges. Through this discussion, we aim to offer a nuanced understanding of the role of DESs in advancing biopharmaceutical stability and delivery strategies.