N-nitrosamine risk assessment in pharmaceuticals: Where are we from a regulatory point of view in 2025?

N-nitrosamines have been a concern for decades due to their potential mutagenicity and widespread occurrence across various matrices. While evidence suggests carcinogenicity in animals, their potential carcinogenicity in humans has prompted their initial inclusion in the “cohort of concern” since in ICH M7(R1), and the current ICH M7(R2) guideline is now in effect. Intensified control of N-nitrosamines began in 2018 following the detection of N-nitrosodimethylamine in valsartan-containing products. Subsequent investigations revealed N-nitrosamine contamination across multiple drug classes, triggering widespread recalls, withdrawals, and regulatory actions. Recently, the emergence of N-nitrosamine drug substance-related impurities and drug linker-related impurities has drawn additional regulatory attention. This review presents the methodologies used to determine the acceptable daily intake of N-nitrosamines and traces the evolution of regulatory guidelines, offering a comparative analysis of the 3-step investigation approaches adopted by the European Medicines Agency and Food and Drug Administration. It provides a comprehensive examination of potential root causes for N-nitrosamine contamination, outlines the analytical requirements for confirmatory testing, as well as mitigation strategies to prevent or minimize contamination. Additionally, the review summarizes risk assessment tools used to predict N-nitrosamine formation. By presenting a comprehensive workflow for impurity investigations, this review aims to assist industrial stakeholders in managing N-nitrosamine risks, ensuring regulatory compliance, and safeguarding public health.