The antidepressant default?
Research Assistant
It is no secret England is experiencing a mental health crisis. With demand for mental health treatment substantially outstripping available supply, the answer is often the most low resource, clinically effective answer available. Enter: medical antidepressants.
The prescription of antidepressants is prolific. In 2023-24, over 15 per cent of people in England, 8.75 million patients, were prescribed antidepressants under primary or community care, 5.45 million of which are on selective serotonin reuptake inhibitors (SSRIs). Comparatively, only 565,550 referrals were made to NHS talking therapies for depression and anxiety.
And yet, the validity of the highly influential serotonin theory of depression — which claims depression is caused by or associated with lower levels of serotonin in the brain, dubbed a ‘chemical imbalance’ — is increasingly questioned.
Last week, the publishing of Professor Joanna Moncrieff’s new book, Chemically Imbalanced: The Making and Unmaking of the Serotonin Myth, landed the most recent blow to the theory.
On Radio 4, Professor Moncrieff explained her book aims to bring awareness to the fact “the idea that depression is caused by a deficiency of serotonin has not been established”. And in 2022, doubts about the theory became more mainstream in academic circles, following a high profile Molecular Psychiatry research review which concluded “there is no convincing evidence that depression is associated with, or caused by, lower serotonin concentrations or activity”.
Despite doubts levelled against the theory, it is still commonly used to justify prescribing antidepressants. Indeed the serotonin theory is still widely believed, with 85-90 per cent of the public believing depression is caused by low serotonin or a chemical imbalance.
Evidence for the serotonin theory is certainly, at best, mixed. Given the medicalisation of depression, the lack of definitive evidence for the theory underpinning the prescribing of antidepressants is incredibly concerning.
With this said, ambiguity around drugs is not necessarily unusual. The human body is complicated and many drugs react differently even in very similar people. Therefore, if the evidence antidepressants worked was itself strong, and it was only unclear why they worked or what the explanatory theory is, then doubts around the serotonin theory of depression would not matter. Take paracetamol. It has been in use as a painkiller for over 70 years and exactly how it works is still not understood.
However, the evidence for antidepressants themselves is complicated and mixed. The efficacy of antidepressants has long been up for debate and, despite some positive evidence they work, the patient profile antidepressants are most likely to work for is not clear, efficacy is very different for different people, and most studies demonstrating efficacy are only short term, covering 8-12 weeks.
Of course, a silver bullet solution for depression — in the form of affordable, easy-to-prescribe antidepressants — would be transformational, and indeed, antidepressants have changed the lives of many people.
But clearly this is not working for enough people. Despite sky high prescription numbers, the prevalence of mental health issues continues rising and economic inactivity as a result of poor mental health is higher than it has ever been. Something is evidently not working. Antidepressants may give the illusion of a silver bullet for mental health, but there is an obvious gap between how many people are being treated and how many people find treatment effective.
Alternative treatment options have consistently been de-prioritised and a more coherent approach is needed in finding new, clinically effective, cost efficient, evidence-backed treatment options. For example, there is promising evidence for the efficacy of AI-powered cognitive behavioural therapy and talking therapy.
Medical interventions, when appropriate, can be lifechanging. But over-medicalisation, when it happens, can carry significant unintended consequences. As the mental health crisis persists and the debate surrounding the serotonin theory of depression mounts, it is important the antidepressant default comes with caveats. Patients need to be fully informed of the pros and cons of antidepressants (and have alternative options available to them), and a coherent strategy searching for better treatment options should be pursued.