Defined daily dose (DDD).
The WHO's assumed average adult maintenance dose, used to compare prescribing volumes across drugs and strengths.
A defined daily dose is the World Health Organization's assumed average maintenance dose per day for a medicine's main adult indication. Divide total milligrams dispensed by the DDD and you get a volume figure that survives comparison across strengths, formulations and even different drugs in a class.
It is an analytical unit, not clinical advice; nobody should take a DDD. Its value is that items and quantity stop working the moment you compare a 10mg tablet with a 40mg one, and DDDs keep working. Their weakness is the assumption itself: where UK dosing practice differs from the WHO assumption, DDD counts drift from reality.
Quantity · The units dispensed within an item: tablets, millilitres, grams. Useful, and easy to aggregate into nonsense.
Items (prescription items) · One item is one product on one prescription form, dispensed once. It is the unit of NHS prescribing volume, and it is not a patient.
See it on a real molecule.
Every molecule page uses this term somewhere: in the scorecard, the charts or the honesty strip. The definitions live here; the numbers live there.