November 25, 2021

It’s not as strange a question as it might sound. Does depression exist? I don’t mean to imply that those with depression should just “pull themselves together”: of course depression symptoms exist (and are sometimes life-ruining). And of course those symptoms often overlap with each other, which certainly implies that there’s a common cause. But is there a thing we can point to in someone’s brain — or some identifiable part of their psychology — that’s called “depression”?

In their understandable desire to get on with trials that might help people who are suffering, many researchers have sidestepped the question of what depression actually is. Instead, they’ve simply agreed on a definition and stuck to it. The Beck Depression Inventory is a questionnaire routinely used to diagnose and define depression: if you’ve ever spoken to your GP about feeling low, you might have come across it. It’s named after Aaron Beck, one of the most important figures in the history of psychiatry (who died aged 100 on November 1st this year). He came up with 21 questions that cover guilt, feelings of failure, weight loss, insomnia, and suicidal thoughts, among other common depressive complaints.

The problem is that the medical profession, and psychiatry researchers, might be relying a little too much on that list of symptoms. Indeed, in an odd, unintentional, circular move, they might have actually turned lists of symptoms into the very definition of depression. An essay by the eminent psychiatrist Kenneth Kendler argues that this is a fundamental mistake: the number of boxes a patient ticks on the list of symptoms that get you a diagnosis isn’t the same as “depression” (nor is their Beck Depression Inventory score) — even if psychiatrists and researchers often act like it is. The Inventory is very often used as the criterion for improvement in studies of treatment: if you achieve a 50% drop in symptoms as measured on his questionnaire, you count as having been positively affected by the treatment. But these criteria are a decent index of many of the common symptoms — not all of them. We know anxiety commonly comes alongside depression, Kendler notes, but it’s not on the standard diagnostic list. If we confuse the disease itself with a useful-but-limited list of its manifestations, we’ll find it harder to truly understand patients’ experiences.

Some researchers have gone a step further: should we stop using the concept of “depression” entirely? One study of thousands of depression patients found over 1,000 unique combinations of symptoms that all still count as “depression”. Maybe it’s time, argue some, to focus on understanding subtypes, or even just specific symptoms, rather than the monolithic entity of “depression” itself.

In some senses — and perhaps ironically — this accords with Beck’s philosophy: he was known for being sceptical of focusing on the ultimate, root causes of mental illness. Which brings us to the other major contribution for which he is remembered: Cognitive Behavioural Therapy. Beginning in the 1960s, Beck reacted against the most popular form of therapy at the time, which was based on Freud’s psychoanalytic theories of the mind. Beck — who himself was originally trained to administer psychoanalytic therapy — began to doubt that depression symptoms were always caused by childhood traumas and unconscious repression. Some of the Freudian theories were rather far-fetched — as Tony Soprano says to his psychoanalytic therapist, after she suggests for the umpteenth time that he might be harbouring some Oedipal desires: “I don’t wanna fuck my mother! I don’t give a shit what you say — you’re never gonna convince me!”

Instead, Beck suggested a much more proximal reason for the disorder: depression patients (and those with other disorders) are suffering from “thought distortions”. For example, they might catastrophise, blowing minor unfortunate occurrences in life out of all proportion. They might overgeneralise, thinking that a fallout with one friend means that they’re hated by everyone they know. As well as focusing his Depression Inventory on these kinds of thought patterns, Beck argued that therapy should target them and train patients out of them, rather than looking for some underlying explanation for all their symptoms.

Beck won the argument: although psychodynamic therapy still exists, CBT has now become the most popular — and by far the most studied — type of psychotherapy. New guidelines, announced this week, give patients the option of group CBT as the first line of treatment for mild depression; but even before then, it was extremely widely used. Its application goes well beyond depression: the language of CBT, with all its ideas about catastrophising and perfectionism and self-blame, is now, as Scott Alexander has memorably argued, “in the water supply”. But “popular” and “culturally influential” doesn’t necessarily mean “good”. What do the studies say about whether it works?

Despite the sheer volume of research, the evidence is actually quite poor. The meta-analyses (reviews of all the studies that have looked at a particular question) do conclude that CBT works compared to doing nothing (a common control group, to which the therapy is compared, is made up of people who are on a waiting list for treatment). But it’s worth remembering that positive studies are more likely to be published than ones concluding that the experiment in question doesn’t work. And the overall literature on psychotherapy does show signs of this kind of bias.

So, even if the studies are right that CBT is beneficial (and in my view they most likely are), the extent of the benefit might be somewhat exaggerated. Those meta-analyses compare CBT to other common forms of psychotherapy, including the psychoanalytic kind (these days usually called “psychodynamic” therapy). The general picture is this: the effects of CBT are essentially the same as any other kind of psychotherapy. They all reduce depression symptoms, and they all still seem to work up to a year later (this particular kind of meta-analysis has to assume all the trials are comparable, though — and that’s often quite a big assumption).

It’s a very similar story for drugs: the meta-analyses show that essentially all forms of antidepressant work better than placebo. But these effects are likely a bit overblown by all the dodgy practices in the scientific literature. And the evidence for one antidepressant being substantially better than another is, to use the kind of language one often sees in the review studies, “limited” (which means researchers only have the vaguest clue).

Although this is good news in one sense, it’s worrying (even depressing) in another. There is evidently a gaping hole in our evidence base on treating depression. If essentially all the major therapy types work to the same degree, despite being based on entirely different — often opposing — principles, it’s pretty difficult to pin down exactly why they work. What exactly are the therapists doing in their sessions that makes the treatment effective? Can we really say that Beck was correct about CBT being the best treatment if other forms of therapy, which take an entirely different approach, can do the same job?

Maybe it doesn’t matter whether therapists stick to Beck’s plausible cognitive theories or Freud’s absurd psychosexual ones. Maybe just having a regular interaction with a smart, sympathetic, well-organised person who focuses on your problems is what helps. That wouldn’t explain, though, why the analyses showed that some forms of self-directed therapy can also make a difference. Either way, all this raises the question: how can we make our therapies better if we don’t know the active ingredients? But then, how can we establish the active ingredients if we don’t even know what we’re treating?


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