There is a provocative meta-analysis suggesting the cognitive behavioral therapy (CBT) may be losing its effectiveness as a treatment of depression. This is important if it’s true, because CBT is the most extensively studied and, possibly, most widely practiced form of psychotherapy. It began as a treatment for depression, but now gets used for all kinds of things, like insomnia. There’s lots of evidence that it works.
The problem is that it might not be working as well as it used to. In the Psychological Bulletin, Tom Johnsen and Oddgeir Friborg found 70 studies of CBT (only 17, however, were actual randomized clinical trials) for depression that were published from 1977 through 2014. As everyone else finds, the data showed that CBT works.
But Johnsen and Friborg then regressed statistical measures of the size of CBT’s treatment effect on the year of publication.
The metaregressions examining the temporal trends indicated that the effects of CBT have declined linearly and steadily since its introduction, as measured by patients’ self-reports (the [Beck Depression Inventory], p < .001), clinicians’ ratings (the [Hamilton Research Scale for Depression], p < .01) and rates of remission (p < .01). Subgroup analyses confirmed that the declining trend was present in both within-group (pre/post) designs (p < .01) and controlled trial designs (p < .02). Thus, modern CBT clinical trials seemingly provided less relief from depressive symptoms as compared with the seminal trials.
Here’s a scatterplot of the data with a fitted line illustrating the decline in effectiveness.
The authors do not have a compelling explanation for why this has happened. Has study methodology become more rigorous over time, shrinking the apparent effectiveness of CBT? Maybe, but there’s no evidence of that. Was there an initial placebo effect that enhanced CBT that has gradually worn off? Has the practice (or practitioners?) of CBT changed somehow? Again, the checks that the authors were able to carry out do not seem to support that. Is the nature of depression changing, somehow, in a way that makes CBT less effective?