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N-nitrosamine (NA) impurities have emerged as a critical safety concern in pharmaceutical manufacturing since the 2018 discovery of N-nitrosodimethylamine (NDMA) contamination in valsartan, which triggered global recalls and revealed similar issues in metformin, ranitidine, and rifampicin. Classified as Class 1 mutagenic carcinogens under ICH M7(R1) and Group 2A carcinogens by IARC, these compounds form through nitrosation reactions between secondary/tertiary amines and nitrosating agents. Contamination can arise from a number of sources including API synthesis (solvent degradation, azide quenching in sartan manufacture), excipient-drug interactions leading to complex nitrosamine drug substance-related impurities (NDSRIs), packaging materials (rubber components, blister packs), environmental water treatment processes, dietary sources (cured meats, tobacco) and endogenous gastric formation. Nitrosamines are zwitterionic resonance structures which are bioactivated by cytochrome P450 into reactive diazonium ions, which form carcinogenic DNA adducts, especially O6-methylguanine, leading to mutations and epigenetic silencing of tumour suppressor genes. Regulatory agencies (FDA, EMA, WHO) have adopted the Carcinogenic Potency Categorisation Approach (CPCA) in which compounds are placed in five potency categories with allowable intakes of 18 to 1500 ng/day with required risk assessment, confirmatory testing and remediation. Detection is carried out using very sensitive GC-MS/MS and LC-MS/MS platforms capable of quantifying contaminants at parts per billion levels and with rigorous sample preparation using nitrite scavengers to prevent artifactual nitrosation. Despite regulatory progress, major gaps remain in the toxicological characterisation, human-specific ADME data, and low-dose combined exposure effects of NDSRIs. Continued research, in silico prediction, green chemistry strategies, and international regulatory harmonisation are needed to protect the integrity of the drug supply and patient safety.