Introduction: Diltiazem hydrochloride (DH) is a calcium channel blocker used in the treatment of hypertension, angina pectoris, and arrhythmias. Its short half-life and frequent dosing requirements limit patient adherence and cause plasma concentration fluctuations. Objective: This review critically examines recent pharmaceutical technologies and formulation strategies for modified-release dosage forms (MRDFs) of diltiazem hydrochloride, emphasizing their impact on pharmacokinetics, clinical performance, and regulatory aspects. Methodology: A structured literature review (2010–2025) was conducted using databases such as PubMed, ScienceDirect, MDPI, and ACS Publications. Studies were selected based on relevance to solid oral MRDFs of DH and their associated manufacturing techniques. Results: Techniques including direct compression, granulation, extrusion–spheronization, spray drying, solvent evaporation, and ionotropic gelation have enabled the development of hydrophilic matrices, coated pellets, microspheres, and osmotic systems. Functional polymers such as HPMC, Eudragit^®, and ethylcellulose play a central role in modulating release kinetics and improving bioavailability. Conclusions: This review not only synthesizes current formulation strategies but also explores reverse engineering of ideal release profiles and the integration of advanced modeling tools such as physiologically based pharmacokinetic (PBPK) modeling and in vitro–in vivo correlation (IVIVC). These approaches support the rational design of personalized, regulatory-compliant DH therapies.