The survey applied a validated questionnaire to distinguish drug treatment side effects from the symptoms of major depression.
A new three-country survey found that 46 percent of patients receiving antidepressant medication for major depression experience emotional blunting. The survey applied a validated questionnaire to distinguish drug treatment side effects from the symptoms of major depression.
Guy Goodwin, DPhil-neurophysiology, University of Oxford, Oxford, UK (pictured) and colleagues acknowledge that many patients treated successfully with antidepressants report that they have less emotional pain than during their depressive episode.
"However, many treated patients also report that they suffer from a restriction in the range of emotions that they associate with normal living, such as the ability to cry or to feel enjoyment," they remarked.
Although there have been publications suggesting that the phenomenon is common, Goodwin and colleagues note that there have been no large-scale epidemiological studies. The researchers undertook the survey in populations in the U.S., U.K. and Canada to ascertain prevalence of the condition and identify related factors.
The internet-based survey was conducted through market research networks rather than clinical research panels, with consumers who had given explicit consent to participate in medical surveys. The populations were English-speaking and 18 years of age or older. The survey was offered to 66,000 individuals in the U.S., 40,000 in the U.K. and 98,000 in Canada.
The first part of the survey identified participants as either patients with depression treated with an antidepressant for at least two months and with complaint of emotional blunting or those who had recovered from depression and had not received medication for at least two months, who would serve as the control group. The final study cohort comprised 854 patients on antidepressants and 150 recovered controls.
The second part of the survey applied the Hospital Anxiety Depression (HAD) scale, and the Oxford Questionnaire on the Emotional-Side Effects of Antidepressants (OQESA). Goodwin and colleagues explain that the questionnaire had been tested on previous samples of depressed patients, and found to have high construct validity and reliability.
"There was a highly significant difference in scale score for patients identified with emotional blunting and the recovered control group, not taking antidepressants, in the present study," Goodwin and colleagues observe. "Moreover, this difference was also present when treated patients and controls were matched for current depressive symptoms. Blunting is, therefore, associated with antidepressant treatment as expected."
The investigators found emotional blunting reported by 46 percent of treated depressed patients, with slightly more frequency in men (52 percent) than women (44 percent). Depressed patients with emotional blunting had significantly higher total blunting scores on OQESA than controls. There was no statistically significant difference between antidepressants, although there was a trend of fewer reports with bupropion (Wellbutrin, GlaxoSMithKline) and more with duloxetine (Cymbalta, Lilly).
Although they had distinguished the emotional blunting as drug side effect from illness symptom, there was an interaction with depression symptom severity. Those with higher HAD-D score >7 had a total OQESA score of 49.23±12.03 that was statistically significantly higher than those with HAD-D<7, 35.07±13.98. Those with the lower HAD-D scale score had a significantly higher OQESA score than the recovered controls who were not on medication, 25.73±15.00.
"The strong association with depression means we believe the description of the scale (OQESA) should be neutral in relation to the causes of emotional blunting which may be multiple," Goodwin and colleagues indicate. "Indeed, the scale remains a work in progress requiring more data collected under double blind conditions..."
The study was published on-line June 6 in the Journal of Affective Disorders.