Analytical Method Validation and Forced Degradation Studies of Drug Substances and Drug Products: An Overview of Principles, Regulatory Guidance, and Current Practices

The development of validated stability-indicating analytical methods is a cornerstone of pharmaceutical development and quality assurance. Forced degradation (stress testing) studies, as recommended by international regulatory guidelines, provide the experimental foundation for characterizing drug substance and drug product degradation behavior, establishing degradation pathways, identifying and structurally elucidating degradation products, and demonstrating analytical method specificity. Despite a well-established regulatory framework centered on the ICH (International Council for Harmonisation) Q1 series, Q2(R2), Q3A/B, and the emerging Q14 guideline, consolidated overviews of methodology, regulatory expectations, and current analytical practice remain limited in scope. This overview examines the published literature on forced degradation study design, degradation chemistry, analytical techniques for degradant characterization, and ICH Q2(R2)-compliant method validation as applied to pharmaceutical drug substances and drug products, providing an integrated, regulation-aligned reference framework applicable to small-molecule drug substances and drug products. A structured literature search was conducted, and regulatory guidance documents from ICH, FDA (Food and Drug Administration), EMA (European Medicines Agency), and WHO (World Health Organization) were reviewed. Sources were selected based on their relevance to forced degradation methodology, degradant characterization, and analytical method validation for pharmaceutical drug substances and drug products. Pharmaceutical drug substances and drug products are susceptible to hydrolytic, oxidative, photolytic, thermolytic, and humidity-induced degradation under stress conditions. The commonly accepted 5% - 20% degradation target is generally considered sufficient to generate primary degradants without secondary degradation artefacts. Reversed-phase HPLC (RP-HPLC) coupled with photodiode array (PDA) detection remains the predominant analytical platform; hyphenated techniques including LC-MS/MS, LC-HRMS, and NMR are frequently employed for degradant identity confirmation above ICH Q3B(R2) reporting, identification, or qualification thresholds. Mass balance in the range of 95% - 105%, combined with full ICH Q2(R2) validation covering specificity, linearity, accuracy, precision, limit of detection (LOD), limit of quantitation (LOQ), and robustness, is widely regarded as the current standard for demonstrating the stability-indicating character of an analytical method. This overview provides a comprehensive