Both benzodiazepine and opioid analgesic dose were measured with an “as prescribed” approach, which assumes that patients took their benzodiazepines and opioid analgesics according to the prescribers’ instructions. Patients were assumed to be taking the maximum amount described in the prescription, including for “as needed” prescriptions. We calculated dose by adding all diazepam or morphine milligram (mg) equivalents in each prescription and dividing by the number of days’ supply. This dose represented the maximum daily dose prescribed and not necessarily the amount actually consumed. If there was an overlap between two prescriptions of the same drug at the same dose and schedule, we assumed that the first prescription was finished before the second prescription was started rather than assuming a higher amount of drug was taken during the overlap. If the overlapping drugs were of a different type, dose, or schedule, than we assumed the second prescription to have started on the date it was filled. Both benzodiazepine and opioid analgesic dose were treated as time varying.