**1. Introduction**

Lipid-based drug delivery systems (LBDDs) have been intensively investigated to overcome various obstacles encountered in oral drug delivery including poor aqueous solubility, limited permeability, low therapeutic window, first pass metabolism as well as inter- and intraindividual variability in drug response [1]. Lipid-based nanoparticles can achieve high loading capacity of hydrophilic and hydrophobic drugs [2]. The delivery features of these drug delivery systems could be tailored to achieve either immediate or sustained release properties depending on the appropriate selection of lipid composition. Most of lipids employed in the formulation are generally recognized as safe (GRAS), biocompatible and biodegradable [3]. LBDDs can enhance both transcellular and paracellular transport of drugs by transient disruption of lipid bilayer cells and alteration of tight junction by products of lipid digestion, respectively. Interestingly, they could permeate challenging physiological barriers such as blood brain barrier without surface

modification due to their lipophilic nature [4]. Further, they are promising carriers for protection of therapeutic peptides against harsh GI environment [3]. Ease of preparation, cost effectiveness and possibility of large-scale production make LBDDs more attractive compared to polymeric nanoparticulate delivery systems [5].
