Antidepressants, cognition, and Cognitive Therapy
 

The British Journal of Psychiatry has an interesting article that tries to explain the mechanisms of action for antidepressant medication and explores how that relates to CT. Harmer et al (2009) propose that "at a neuropsychological level, antidepressants act by remediating negative affective biases in depression and anxiety and that these actions occur relatively quickly following drug administration. Such changes in bias are probably not accessible to subjective state, but the effects of processing emotional and social stimuli in a more positive manner would be expected to lead to gradual changes in social reinforcement, behaviour, and mood over time" (thus resulting in decreased depression several weeks after medication has been started).

They discuss quite a bit of empirical data, including brain imaging studies, which support their theory and discuss some interesting implications such as "Treatment failure [for antidepressants] may be particularly associated with an adverse interpersonal environment or long-standing negative attitudes, such tthat changes in automatic emotional biases are insufficient to produce a satisfactory antidepressant effect. In contrast, failure of cognitive therapy may arise because the primary automatic biases are too fixed to allow a conscious remodelling of appraisal and evaluation...in these circumstances combining antidepressants with cognitive-behaviour therapy might be more effective than increasing the 'dose' of either therapy alone."

Take a look at:

Harmer, C. J., Goodwin, G. M. & Cowen, P. J. (2009). Why do antidepressants take so long to work? A cognitive neurological model of antidepressant drug action. The British Journal of Psychiatry, 195, 102-108.