Abstract
Over the past twenty years, ionic liquids (ILs) and deep eutectic solvents (DESs) have gained recognition across various fields, including catalysis, extraction and purification, materials science, and biotechnology. Notably, the use of ILs and DESs in pharmaceutical research, especially in drug delivery, has seen remarkable expansion over the past decade. This review offers a comprehensive analysis of ILs and DESs specifically designed for the oral administration of drugs having unfavorable biopharmaceutical properties. The classification and characteristics of ILs and DESs, along with their newer natural (Bio-ILs and NaDESs) and therapeutic subcategories (API-ILs and TheDESs) are outlined. Additionally, a further subgroup of ILs, known as surface active ionic liquids (SAILs), is described. Then, a detailed examination of the available manufacturing methods in a sustainable, time-consuming, and scalable perspective, and toxicity concerns in relation to their subdivision are evaluated. Finally, their specific applications in oral drug delivery, whether used as neat solvents or converted into administrable dosage forms, are analyzed and discussed. Despite the significant advancements in recent years regarding the use of these solvents in oral drug delivery, there are still many aspects that need further investigation. These include their interaction with biological systems (gastrointestinal fluids and mucosa), their long-term stability, and the development of effective drug delivery systems.