Is depression related to serotonin?

Executive summary

* This week's note is important. It received media coverage, but it does not appear to have changed medical practice and it presents a compelling case for doing so.

* It reviews a paper by Moncrieff et al, which examined evidence for "the serotonin theory of depression." This is the belief that depression is caused by low serotonin and hence antidepressants work by making serotonin more available.

* The paper was an umbrella review, which meant that it examined all available evidence.

* It asked six research questions, which could examine if depression is the result of (or associated with) low serotonin.

* It found no convincing evidence that depression is associated with, or caused by, lower serotonin concentrations or activity.

* There may be another mechanism by which antidepressants help people. There may be a placebo effect. The evidence does not support the commonly held belief that depression is the result of a 'chemical imbalance', related to serotonin, and that antidepressants work by correcting this.

* This is as important as research gets and it should impact the treatment of depression. I suspect that it won't for a number of reasons.