Abstract: The present disclosure discloses nitrosamine impurities, a varenicline pharmaceutical composition capable of reducing the generation of nitrosamine impurities, and the preparation and use thereof. By means of adding a pharmaceutically acceptable acid to a secondary amine compound or a composition thereof, the pharmaceutical composition of the present disclosure can effectively inhibit and reduce the generation of nitrosamine impurities, improve the stability of the secondary amine compound or the composition thereof, and control the content of genotoxic nitrosamine impurities to be at a relatively low level, so as to comply with safety requirements.