INTRODUCTION: Transdermal patches offer a unique advantage by providing extended therapeutic benefits while maintaining stable plasma drug concentration. The efficacy and safety of patches depend significantly on their ability to adhere to the skin, a feature influenced by various external and internal factors. AREAS COVERED: The review primarily focuses on the fundamental aspects of adhesion in transdermal patches, including basic information about the skin, the underlying principles of adhesion, drug delivery, and adhesion characteristics of pressure sensitive adhesives (PSAs), adhesion issues, impact factors, strategies to improve patch adhesion, and relevant molecular mechanisms. EXPERT OPINION: The development of transdermal patches with sufficient adhesion for consistent and extended drug delivery remains a challenging task. Challenges in adhesion stem from the complex interplay among PSAs, permeation enhancers, active pharmaceutical ingredients (APIs), and other excipients in current patch compositions, further complicated by variations arising from dermatological factors. These intricacies significantly impede the consistent effectiveness of patches. Progress in the exploration of new PSA polymers, in conjunction with innovative patch compositions, is crucial for establishing an optimal equilibrium between drug utilization rate, drug-loading, drug release, and adhesion, thus effectively addressing the challenges related to adhesion.