Suggestibility as a predictor of response to antidepressants: A preliminary prospective trial

The growing awareness that so many do not respond adequately to antidepressant (AD) pharmacotherapy has sparked research seeking to characterize those who do. While the pharmacological mechanisms of AD treatment have been extensively evaluated, much remains unknown about the placebo component of the response to medication. This study examined the association between suggestibility levels and response to ADs amongst depressed patients.

Twenty unipolar depression outpatients, recruited before starting AD monotherapy, received clear, standardized instructions that the therapeutic effects of AD, though not side effects, would require 2-4 weeks. At baseline (T1), 1 week (T2), and 1 month (T3), participants were evaluated for depressive symptoms, using the Hamilton Rating Scale for Depression-17 items (HAM-D); for anxiety by the Hamilton Rating Scale for Anxiety (HAM-A); for side effects by the Antidepressant Side Effect Checklist (ASEC); and for suggestibility, using the Multidimensional Iowa Suggestibility Scale (MISS).

High levels of baseline suggestibility were associated with less improvement in depression level and more side-effects during the first week. In accordance with our hypothesis the more suggestible patients improved more between T2 and T3. No significant correlations were found between baseline suggestibility levels and change in anxiety.

Small sample size and a self-report questionnaire assessing suggestibility were limitations.

This study offers a potentially new and clinically useful approach to understanding and predicting who will respond to AD treatment. Suggestibility seems to play a role, presumably by shaping expectation, in response to AD treatment. We hope that this avenue will be further explored.