Is mental illness a chemical imbalance?

This week Kat Arney's been looking at a myth that's all in the mind...

Kat - Mental health problems are widespread in society, with around one in four people experiencing some kind of mental health problem, according to the charity MIND. These include depression, anxiety, post-traumatic stress disorder, eating disorders and more. Then there are other conditions such as schizophrenia and bipolar disorder.  But even more widespread than the incidence of mental health problems is the belief that mental illness is caused by an imbalance of chemicals in the brain, with an Australian survey finding that a staggering 86 per cent of adults believe this is the cause.

What's more, pharmaceutical companies that develop and sell treatments for conditions such as anxiety and depression have referred to the idea of 'chemical imbalance' in their marketing materials. But although it's a neat explanation for how things go wrong in the brain in mental illness - it's not really correct.

So where did the idea come from? It seems to date back to the 1950s, when some of the first drugs for mental illness came on the market. They had impressive effects on people's symptoms, and seemed to be boosting the levels of certain chemicals in the brain known as neurotransmitters. These are molecules that shuttle between nerve cells in the brain, sending messages and passing on signals. So the natural assumption was that if ramping up the levels of neurotransmitters fixed the problem, then the problem must be caused by having the wrong level to start with.

Unfortunately this isn't borne out in reality. For example, it's commonly believed that people with depression suffer from low levels of the so called 'happy' neurotransmitter serotonin. But research has discovered they're not particularly lacking in it. And two different drugs - one of which boosts serotonin, the other reduces it - can have similar effects on mental health symptoms. So clearly it's not that simple.

It's tempting to try and pin everything on our biology, but it ignores the fact that the environment plays a big role, and people can take steps towards recovery. On the flip side, a recent German study suggested that people who believe in the chemical imbalance theory tend to have more negative reactions to people with depression than people who don't. Another test with people who had experienced depression showed that if they were given a spoof lab test suggesting that their serotonin was out of whack, they were more pessimistic about their chances of recovery and less confident of their ability to manage their depression. They were also more likely to shun psychotherapy in favour of taking prescription drugs.

So what do we know? Our brains aren't a set of chemical balancing scales, and life's just not that simple. Clearly, much more work does need to be done into understanding the causes of mental illness and how best to treat them, while avoiding stigmatising sufferers. And for the one in four of us that suffers from mental health problems, that can't come soon enough.