The defined daily dose (DDD) is a statistical measure of drug consumption, defined by the World Health Organization (WHO) Collaborating Centre for Drug Statistics Methodology. It is defined in combination with the ATC Code drug classification system for grouping related drugs. The DDD enables comparison of drug usage between different drugs in the same group or between different health care environments, or to look at trends in drug utilisation over time. The DDD is not to be confused with the therapeutic dose or prescribed daily dose (PDD), or recorded daily dose (RDD), and will often be different to the dose actually prescribed by a physician for an individual person.

The WHO's definition is: "The DDD is the assumed average maintenance dose per day for a drug used for its main indication in adults." The Defined Daily Dose was first developed in the late 1970s.