This review by Thorsteinn Loftsson, Hakon Hrafn Sigurdsson, and Phatsawee Jansook pulls a brave topic. It accounts some of the unexpected results the authors have encountered during their studies of CDs as pharmaceutical excipients.
CDs are constantly surprising investigators with their unique physicochemical properties. CDs are solubilizing complexing agents of poorly soluble drugs in aqueous solutions, while they can also act as organic cosolvents like ethanol. CDs and their complexes self-assemble in aqueous solutions to form both nano- and microparticles. The nanoparticles have diameters that are well below the wavelength of visible light; thus, the solutions appear to be clear. However, the nanoparticles can result in erroneous conclusions and misinterpretations of experimental results. CDs can act as penetration enhancers, increasing drug permeation through lipophilic membranes, but they do so without affecting the membrane barrier.
See the full article here: Anomalous Properties of Cyclodextrins and Their Complexes in Aqueous Solutions