In pharmacology, an active moiety is the part of a molecule or ion – excluding appended inactive portions – that is responsible for the physiological or pharmacological action of a drug substance.  Inactive appended portions of the drug substance may include either the alcohol or acid moiety of an ester, a salt (including a salt with hydrogen or coordination bonds), or other noncovalent derivative (such as a complex, chelate, or clathrate).  The parent drug may itself be an inactive prodrug and only after the active moiety is released from the parent in free form does it become active.