Regular readers will be familiar with the idea that "antidepressants only work in severe depression".
A number of recent studies have shown this. I've noted some important questions over how we ought to define "severe" in this context, and see the comments here for some other caveats, but I'm not aware of any studies that directly contradict this idea.
Until now. A new paper has just come out which seeks to challenge this dogma - not the author's term, but I think it's fair to say that the severity theory is becoming a dogma, even if it's an evidence-based one (but then, all dogmas start out seeming reasonable).
However, while the new paper is interesting, I think the dogma survives intact.
The authors went through the archives of all of the trials of antidepressants for depressive disorders conducted at the famous New York State Psychiatric Institute for the past 30 years. They excluded any patients who were severely depressed, and just looked at the milder cases. The drugs were mostly the older tricyclic antidepressants.
With a mean HAMD17 score of about 14, the patients they looked at were certainly mild. By comparison, most trials today have a mean of well over 20, and according to the main studies supporting the severity dogma, you need a score of about 25ish to benefit substantially:
So what happened? They reanalyzed 6 trials with over 800 patients. Overall there was a highly significant effect of antidepressants over placebo in mild depression, with an effect size d=0.52, or about 3.5 HAMD points. This is actually better than most other studies have found in "severe" depression. If valid, these results would torpedo the severity theory.
This seems very interesting... but. There's a big but (I cannot lie). Although the authors say they wanted to include all the relevant trials from the NYSPI, they only had access to the data from 6. There were another 6 projects, but they were "pharmaceutical company studies from which data were not released to the investigators."
This pretty much wrecks the whole deal. If those 6 studies all found no benefit of the drug, the overall average results would be much less impressive. We have no way of knowing what those studies found, but I'd wager that most of themwere negative, because of publication bias - we know that drug companies tend to publish positive studies and bury negative ones. Or at least they did, at the time these studies took place (there are better regulations now).
By contrast, severity dogma classic Kirsch et al (2008) avoided publication bias by looking at unpublished data. Fournier et al (2010), the other major severity study, didn't but the data were very similar to Kirsch et al so it's not hard to believe them.
So in my view, until we know what happened in the other 6 trials, we can't really interpret these results, and the severity theory stands.
Stewart, J., Deliyannides, D., Hellerstein, D., McGrath, P., and Stewart, J. (2011). Can People With Nonsevere Major Depression Benefit From Antidepressant Medication? The Journal of Clinical Psychiatry DOI: 10.4088/JCP.10m06760