Explanation of terms used by DrugBank

Molecular Weight

The molecular formula of a drug or chemical substance is a type of chemical formula that typically denotes the specific number of each kind of elemental atom that makes up the drug or substance. Each element is furthermore associated with a unique atomic weight that describes the physical weight of a single atom of the element 1. The molecular weight of a drug or chemical substance is subsequently the sum total addition of the atomic weights of all the particular elemental atoms that make up the drug or substance. Molecular weight is generally recorded in the unit of grams per mole (g/mol).

As an example, the molecular formula for water is H2O.  This formula denotes that there are two hydrogen atoms and one oxygen atom. As the given atomic weights for hydrogen and oxygen elements are approximately 1.00784 and 15.99903 respectively 1, the molecular weight for one molecule of H2O water is (2 atoms of hydrogen x 1.00784 atomic weight per atom of hydrogen) + (1 atom of oxygen x 15.99903 atomic weight per atom of oxygen) = 18.01471 g/mol.


  1. CIAAW Standard Atomic Weights of the Elements [Link]