PubChem is a free online database that provides information on chemical substances and their biological activities. It is maintained by the National Center for Biotechnology Information (NCBI) and is part of the National Institutes of Health (NIH) in the United States. Users can search for chemicals, compounds, and their properties, including molecular structures, toxicity, and biological effects. The database includes data from various sources, such as scientific literature and chemical suppliers. PubChem is widely used by researchers, educators, and students to access reliable chemical information and to support drug discovery and development efforts in the field of biochemistry and pharmacology.