However, in addition to the permeation of small molecules and macrocyclic peptides with mostly nonpolar sidechains, it has recently been discovered that polar, linear peptides like semaglutide can very likely also pass directly through membranes with the help of permeation enhancers like salcaprozate sodium (SNAC, Fig. ) . This new finding cannot be readily explained with the currently available mechanistic models, and it is still mostly unknown how this permeation enhancer-facilitated process occurs.