Serotonin systems: should we ditch the antidepressants?

Antidepressant use is rising fast. In fact, the number of prescriptions in the UK doubled in just10 years, between 2008 and 2018. Yet, the value of antidepressants has been hotly debated in psychology.

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Psychiatrists on one side quote research that claims antidepressants — specifically selective serotonin re uptake inhibitors (SSRIs) like citalopram and Prozac — have excellent results in treating low mood. 

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On the other side, psychologists and psychotherapists highlight the impact of real-world events (like poverty, stress or trauma) and internal struggles (such as lack of motivation or loneliness) as causes of depression. 

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Collectively deciding on the best approach to treating depression is vital. Depression is the most common mental health problem worldwide, and we need to get better at understanding it. So, what factors are behind the two sides of this argument — and what’s our stance on it?

Debunking the serotonin hypothesis

You might’ve seen the press coverage of the most recent research from the team at University College London led by Dr Joanna Moncrieff that seemed, at first glance, to settle the issue once and for all.

The study, ‘The serotonin theory of depression: a systematic umbrella review of the evidence’, was an umbrella review of studies over the last 50 years on the efficacy of SSRIs in treating depression. The review found ‘no clear evidence’ that low serotonin levels cause depression. 

The Guardian quoted Moncrieff: ‘It is always difficult to prove a negative, but I think we can safely say that after a vast amount of research conducted over several decades, there is no convincing evidence that depression is caused by serotonin abnormalities’.

In addition, we know that antidepressants cause side effects like nausea, insomnia and withdrawal effects for some people. So, we don’t want to give tablets to people when we don’t know if or how they work — or when they’ll cause harm fora minority of patients.

Experts have known for decades that SSRIs change serotonin levels almost immediately but take at least a couple of weeks to make a difference to mood (although, annoyingly, the side effects kick in pretty much straight away). If depleted serotonin levels caused depression, antidepressants would begin to work on mood levels within hours, not weeks.

Research has also proven that psychotherapy works in treating depression — especially treatments recommended by the NationalInstitute for Health and Care Excellence (NICE), such as cognitive behavioural therapy (CBT). Many of us are also inherently sceptical of Big Pharma, often with reasonable justification. 

Case closed, then?

Not so fast. As with most things to do with mental health, it’s a little more complicated than that…

Examining the bio psychosocial model

Let’s look a bit closer at the review by Moncrieff and her team. What it didn’t claim was that antidepressants don’t work. Instead, it examined the specific ways SSRIs work: by reducing the ‘re uptake’ of serotonin in the brain, thereby increasing serotonin levels.

However, it’s been common knowledge for decades that the ‘serotonin hypothesis’ isn’t an adequate explanation for depression. As part of recent criticism of Moncrieff’s paper by the Royal College of Psychiatrists, Professor Gitte Moos Knudsen from Copenhagen University Hospital noted that today, it’s broadly accepted that depression is ‘a heterogeneous disorder with potentially multiple underlying causes’.

This idea is often described as the ‘bio psychosocial’ model that acknowledges the biological, psychological and social impacts on mental health — one that the vast majority of the field of psychology ascribes to now. 

One metaphor for this model uses headaches as an example. People don’t believe a lack of paracetamol causes headaches, citing plenty of other variables that might be the cause, but we pop a pill and see a reduction in the pain in our heads. Similarly, we don’t need to believe that serotonin levels cause depression to think that SSRIs can work to improve mood. 

It’s possible, and maybe even likely, that some people have a specific kind of depression linked to — not necessarily caused by — changes in the serotonin system. Plus, as antidepressants affect a number of different pathways and receptors in the brain, they have the potential to help people with a range of different types of depression — only some of which are linked to the serotonin system. 

If some cases of depression are linked to changes in serotonin levels, it’s possible that SSRIs could be an effective treatment. But how do we treat the other underlying causes?

Taking a combined approach

It seems self-evident that depression is more complicated than a specific chemical imbalance in the brain. We see people around us responding to life events and struggling to make it out of the fog.

The current evidence suggests that a combination of antidepressants and therapy is the best plan for the treatment of moderate and severe depression. The medication can help improve mood and raise motivation levels, allowing people to engage more proactively with their therapy to a point where it becomes a virtuous circle. We should acknowledge, though, that routine medication use isn’t recommended for treating mild to moderate depression.

In short: depression isn’t caused by low serotonin. But we’ve known that for decades. And antidepressants work for most people, especially in partnership with good therapy. 

So, don’t throw away those strips of citalopram just yet.

Do you struggle with depression? You’re not alone. We provide a range of resources to help you develop the tools to improve your mental health — check out our Introduction to CBT Techniques course!

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