Yum, sugar pills! We talk about them all the time in science, where they have a much more formal and less appetizing name — placebos.
A placebo is simply something used in research to act as a treatment equivalent, so as to not bias either the research subjects or the researchers themselves in how they perceive and react to the experimental treatment. In research on drugs, this often means giving one group of patients pills that look just like the medicine being studied, but lacking any active ingredient.
In recent years, new research has emerged looking solely at the studies that were used to gain FDA approval of antidepressant medications (some of which were never published). When taken together, the studies found that antidepressant medications may not be as effective as previously thought (but what any patient who’s ever tried them could’ve told us decades ago). This recent research found effect sizes of just 0.31.
Which got some researchers to wonder… If antidepressant drug treatment effect sizes might be lower than we had thought, could the same be true for psychotherapy effect sizes too?
Could, in fact, a sugar pill offer as much change in one’s depression as months or years of intensive psychotherapy?
A research study’s effect sizes tell us how different the treatment group is from the control group — the folks taking placebos. A larger effect size means the treatment really worked, a small effect size tells us the treatment isn’t that much different from a sham treatment.
The studies re-examing the data on antidepressants demonstrated new effect sizes that were smaller than we thought they would be. We thought antidepressants had an effect size of anywhere from 0.60 to 0.40. Now we find out their effect size might be as little as 0.31 — a significant difference.
This means that antidepressants — as a class of drugs — simply aren’t as effective as most of us once thought.
“C’mon Doc… Surely psychotherapy — which seeks to make real changes to a person’s thoughts and belief processes — couldn’t fare any worse when compared to a sugar pill, could it?”
Answering this question is tricky, because there are so few studies that have been conducted comparing psychotherapy treatment with a pill placebo control group. That’s because a pill isn’t really equivalent to psychotherapy as a treatment method. It’s like comparing apples to oranges, so in psychotherapy research, the control group is most often what’s called a “wait list” control group.
But you can look at studies that examined an antidepressant medication, a pill placebo, and a psychotherapy treatment group. And there just so happens to be a few such studies out there.
Cuijpers et al. (2013) combed the psychological and psychiatric research literature and found ten studies that compared psychotherapies with pill placebo. In total, 1,240 patients were included in these studies. They pooled the data and ran their statistical meta-analyses on the resulting data.
Here’s what they found:
At the end of clinical trials, the effect size for psychotherapy compared to pill placebo was g = 0.25.1
If we translate that into practical terms of Number Needed to Treat (NNT), 7.14 psychotherapy patients had to be treated in order to get assured of getting one who did better than getting a pill placebo.
Patients in the psychotherapy conditions scored 2.66 points lower on the Hamilton depression rating scale than those assigned to pill placebo. These differences are well within the range of the differences found between antidepressants and pill placebo in the FDA registered trials.
Essentially, when compared to pill placebo, psychotherapy did as well or, if you’d like, as poorly as an antidepressant. So, inferring that psychotherapy is the preferred treatment based simply on the basis of the small differences between antidepressants and pill placebos is not warranted.
In other words, when we look at what limited data we have — and 10 studies of just over 1,000 patients over the course of 20 years isn’t a lot — psychotherapy doesn’t really come out ahead of antidepressant medications.
In fact, according to this one study, it’s actually worse than antidepressants (0.25 versus 0.31), and really not much better than a person taking a sugar pill for treatment (because these effect sizes are so small, they suggest there’s not a significant difference between the placebo and treatment groups).
James Coyne suggests, “both sides should recognize that neither psychotherapy nor meidcation [sic] have the efficacy that we would like to obtain from them in treating depression.” No new antidepressant medication breakthroughs are on the horizon, he notes, nor have any new psychotherapies taken hold in the past twenty or thirty years.
Which leaves us with the knowledge that while the treatments we have may not be as effective as we would like them to be, they remain the best tools we have to combat depression. What research can’t capture or comment upon is the amount of trial-and-error effort that goes into finding the right, effective treatment for each individual. A process that — while frustrating — usually results in the person suffering from depression to find some relief and hope.
For a very lengthy, in-depth discussion of these issues, see: Is psychotherapy for depression any better than a sugar pill?
P. Cuijpers, E. H. Turner, D. C. Mohr, S. G. Hofmann, G. Andersson, M. Berking and J. Coyne. Comparison of psychotherapies for adult depression to pill placebo control groups: a meta-analysis. Psychological Medicine, available on CJO2013. doi:10.1017/S0033291713000457.
- In research, it’s generally accepted that a small effect size is around 0.2, a medium effect size is 0.5 and a strong or large effect size is 0.8. [↩]