International Journal of Scientific Research and Engineering Development

Transdermal drug delivery systems (TDDS) have emerged as a promising, non-invasive alternative to conventional drug administration routes due to their ability to deliver therapeutics through the skin and into systemic circulation in a controlled manner. This approach avoids first-pass metabolism, minimizes gastrointestinal irritation, enhances bioavailability, and improves patient compliance, particularly in populations that struggle with oral or parenteral dosage forms. The structural complexity of human skin, especially the stratum corneum, presents a major barrier to drug permeation, making the design of efficient transdermal systems highly dependent on understanding skin anatomy, physiology, and barrier characteristics. Over the years, significant advancements have been made in the development of formulation strategies and penetration-enhancing techniques to improve drug flux across the skin. Various types of transdermal patches including single-layer, multi-layer drug-in-adhesive, reservoir, and matrix systems have been widely explored and optimized for different therapeutic needs. Complementary technological interventions such as microneedles, iontophoresis, ultrasound (sonophoresis), thermal enhancement, and laser microporation have further expanded the applicability of TDDS to deliver macromolecules, peptides, and hydrophilic drugs that traditionally showed poor permeability. In parallel, formulation innovations involving chemical enhancers, natural permeation agents, eutectic mixtures, Nano emulsions, liposomes, and solid lipid nanoparticles have significantly enhanced drug solubility and transdermal penetration. Evaluation parameters such as folding endurance, moisture content, tack, peel adhesion, and weight uniformity remain critical to ensuring patch quality, performance, and patient acceptability. TDDS have been successfully commercialized for various therapeutic indications including pain management, hormone replacement therapy, smoking cessation, cardiovascular diseases, and neurological disorders. This review highlights the fundamentals, technological advances, formulation approaches, evaluation methods, and current applications of TDDS, emphasizing their growing relevance in modern drug delivery. Continued research in material science, penetration enhancement, and nanotechnology will further broaden the scope of transdermal therapeutics and contribute to more effective, patient-friendly drug delivery solutions.