As interest in oral thin film grows, there is an increasing effort to study new and improved methods of drug delivery in the buccal cavity. Muco-adhesive studies have increased, leading to the introduction of a prescription product approved for chronic pain treatment. This article, from Rick Chan, PhD, Executive Scientific Officer, LTS Lohmann Therapy Systems, will discuss the fundamentals of transmucosal absorption and how formulation effort and the drug properties influence drug absorption in the buccal cavity.