‘Researchers have found that Cognitive Behavioural Therapy is roughly half as effective in treating depression as it used to be’ writes Oliver Burkeman in The Guardian, arguing that this is why CBT is ‘falling out of favour’. It’s worth saying that CBT seems as popular as ever, but even if it was in decline, it probably wouldn’t be due to diminishing effectiveness – because this sort of reduction in effect is common across a range of treatments.
Burkeman is commenting on a new meta-analysis that reports that more recent trials of CBT for depression find it to be less effective than older trials but this pattern is common as treatments are more thoroughly tested. This has been reported in antipsychotics, antidepressants and treatments for OCD to name but a few.
Interestingly, one commonly cited reason treatments become less effective in trials is because response to placebo is increasing, meaning many treatments seem to lose their relative potency over time.
Counter-intuitively, for something considered to be ‘an inert control condition’ the placebo response is very sensitive to the design of the trial, so even comparing placebo against several rather than one active treatment can affect placebo response.
This has led people to suggest lots of ‘placebo’ hacks. “In clinical trials,” noted one 2013 paper in Drug Discovery, “the placebo effect should be minimized to optimize drug–placebo difference”.
It’s interesting that it is still not entirely clear whether this approach is ‘revealing’ the true effects of the treatment or just another way of ‘spinning’ trials for the increasingly worried pharmaceutical and therapy industries.
The reasons for the declining treatment effects over time are also likely to include different types of patients selected into trials, more methodologically sound research practices meaning less chance of optimistic measuring and reporting, the fact that if chance gives you a falsely inflated treatment effect first time round it is more likely to be re-tested than initially less impressive first trials, and the fact that older known treatments might bring a whole load of expectations with them that brand new treatments don’t.
The bottom line is that lots of our treatments, across medicine as a whole, have quite modest effects when compared to placebo. But if placebo represents an attempt to address the problem, it provides quite a boost to the moderate effects that the treatment itself brings.
So the reports of the death of CBT have been greatly exaggerated but this is mostly due to the fact that lots of treatments start to look less impressive when they’ve been around for a while. This is less due to them ‘losing’ their effect and more likely due to us more accurately measuring their true but more modest effect over time.