Joanna Moncrieff, Mark Horowitz

For three decades, people have been deluged with information suggesting that depression is caused by a “chemical imbalance” in the brain – namely an imbalance of a brain chemical called serotonin. However, our latest research review shows that the evidence does not support it.

… At first sight, the fact that SSRI-type antidepressants act on the serotonin system appears to support the serotonin theory of depression. SSRIs temporarily increase the availability of serotonin in the brain, but this does not necessarily imply that depression is caused by the opposite of this effect.

There are other explanations for antidepressants’ effects. In fact, drug trials show that antidepressants are barely distinguishable from a placebo (dummy pill) when it comes to treating depression. Also, antidepressants appear to have a generalised emotion-numbing effect which may influence people’s moods, although we do not know how this effect is produced or much about it.