This document discusses impurities in pharmaceutical products. It defines impurities as foreign substances present in small amounts that make a product dirty or unacceptable. Impurities can decrease shelf life, stability, therapeutic effects and increase toxicity. Sources of impurities include synthesis, formulation, storage, particulate matter, byproducts, microbial contamination and heavy metals. The quality and safety of pharmaceuticals is highly dependent on controlling impurities. Proper purification of raw materials and intermediates during synthesis is important to minimize synthesis-related impurities. Storage conditions must be suitable to prevent storage-related impurity formation. Water is a major source of heavy metal impurities so distilled or demineralized water is preferred. Overall, stringent control of all potential sources