Mianserin is an antidepressant drug that is used to treat depression and anxiety disorders. However, during the manufacturing process of mianserin, impurities can be generated which may affect the efficacy and safety of the final product. These impurities need to be identified, characterized and controlled to ensure the quality of the drug product. Regulatory authorities have set limits on the levels of impurities that can be present in the drug substance and drug product, and manufacturers need to comply with these regulations.