Abstract
Background/Objectives: Extracellular vesicles (EVs) are nanosized carriers with high biocompatibility, low immunogenicity, and the ability to cross biological barriers, making them attractive for drug delivery. Despite growing interest, the clinical translation of drug-loaded EVs remains limited. This systematic review aimed to summarize current evidence on EV sources, loading strategies, therapeutic applications, and translational challenges. Methods: Following PRISMA 2020 guidelines, a systematic search was conducted in Embase, PubMed, Reaxys, and Scopus for the period 2020-2025. Eligible studies included original articles on drug-loaded EVs from human, animal, plant, or other sources. Data on EV source, drug type, particle size, loading method, administration route, and therapeutic application were extracted. Clinical trials were identified through ClinicalTrials.gov. Results: A total of 65 studies were included after screening 5316 records, along with two clinical trials. Human mesenchymal stem cell (MSC)-derived EVs were the most frequent source in oncology, while plant-derived EVs predominated in non-oncology applications. Anti-cancer drugs such as doxorubicin, gemcitabine, and docetaxel were most frequently loaded, alongside curcumin, berberine, and atorvastatin. EV sizes generally ranged from 50 to 200 nm, with larger vesicles reported for plant-derived EVs. Intravenous administration predominated, with most studies demonstrating sustained release and enhanced therapeutic efficacy. Passive loading was most common, especially for hydrophobic drugs, whereas active methods such as electroporation and sonication were preferred for hydrophilic cargo. Two clinical trials showed preliminary therapeutic benefits with favorable safety. Conclusions: Drug-loaded EVs represent a promising and versatile drug delivery platform, yet their clinical translation is hindered by variability in isolation and loading methods, production scalability, and safety evaluation. Further standardization and large-scale studies are needed to advance EV-based therapeutics toward clinical use.