Adjustment to antidepressant utilization rates to account for depression in remission

Conventional estimates of antidepressant (AD) utilization in major depressive syndrome (MDS) have been low, but this may be partially because ongoing AD use by individuals with resolved MDS is not included. Valid estimates of AD utilization should include this ongoing use for MDS, but this is difficult since most surveys do not collect data on the reason for taking ADs. Only a proportion (f(dep)) of the nondepressed (nMDS) population taking ADs does so for depression. Published studies have not reported this proportion, and data required to estimate f(dep) are not usually available from surveys. The current study was performed to (1) estimate f(dep) by employing information on past history of depression, and (2) use the estimate to obtain an "adjusted" AD utilization rate, including resolved MDS subjects taking ADs. Data were collected in Calgary in 1998 and 1999 by random-digit dial telephone interview from consenting adults aged 18+ years. MDS was assessed using the Composite International Diagnostic Interview Short Form for Major Depression (CIDI-SFMD). Data were gathered on current medications, past depression, and current chronic physical illness. Of 2,542 respondents, 17.1% had MDS as defined by the CIDI-SFMD. A total of 20.2% of MDS and 3.2% of nMDS subjects were taking ADs. Of nMDS individuals taking ADs, 70.6% reported past depression (f(dep) = 70.6%). An "adjusted" AD utilization rate including this group was 28.2%. Physical illnesses that can be treated with ADs affected only 30.0% of nMDS subjects without past depression taking ADs. This study suggests that most individuals without active depression taking ADs do so for depression. AD utilization rates that ignore this group may be unrealistically low. AD use among nMDS subjects without previous depression is probably not primarily for physical illnesses. Limitations include the use of a brief predictive instrument for MDS, and self-report of past depression.