Orally disintegrating tablets (ODTs) improve patient compliance, particularly in pediatric and geriatric populations who experience difficulty swallowing conventional tablets. The present study focuses on the formulation and evaluation of diphenhydramine hydrochloride orally disintegrating tablets prepared by the direct compression method. Diphenhydramine HCl, a first-generation antihistamine with anticholinergic and sedative properties, was characterized using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and UV–Visible spectroscopy to assess purity and compatibility with excipients. Various super-disintegrants such as sodium carboxy methyl cellulose (SCMC), sodium alginate, polyvinyl pyrrolidone (PVP), and polyethylene glycol (PEG) were evaluated at different concentrations. Pre-compression and post-compression parameters including angle of repose, compressibility index, Hausner’s ratio, weight variation, hardness, friability, thickness, disintegration time, and wetting time were assessed. Sodium carboxy methyl cellulose demonstrated superior disintegration efficiency and mechanical strength compared to other super-disintegrants. The optimized formulation containing 10% SCMC exhibited rapid disintegration (?10 seconds), acceptable wetting time, and satisfactory mechanical properties. Stability studies conducted under varying temperature and humidity conditions confirmed that the formulation remained stable with drug release between 90–110% as per USP standards. The study concludes that diphenhydramine HCl ODTs formulated using SCMC via direct compression are stable, effective, and suitable for pediatric and geriatric use.