Data from several sources are needed to show numbers taking drugs

EDITOR,—R Bracchi raises the point of how many patients are taking a drug.1 Pharmaceutical companies would very much like accurate data on this to help with calculations of the reported incidence of adverse drug reactions and with commercial monitoring. Several practical difficulties arise. The data cannot be obtained from the point at which prescriptions are measured since not all prescriptions written are dispensed and not all drugs prescibed are consumed.

For a product whose patent is protected—that is, no …