No ‘clear evidence’ depression is caused by low serotonin levels

The new review of existing studies found that the condition is not likely caused by a chemical imbalance and said people should be made aware of other options for treating depression.

However, other experts, including from the Royal College of Psychiatrists (RCP), urged people not to stop taking their medication in light of the findings, and argued that antidepressants are effective.

NHS figures show that the number of people in England taking antidepressants continues to rise, with 8.3 million patients receiving them in 2021/22, a 6% rise on the previous year when the figure was 7.9 million.

The general consensus in the public is that depression is caused by a chemical imbalance (PA) (Image: PA)

Overall, an estimated 83.4 million antidepressant drug items were prescribed in 2021/22, a 5% jump from the previous year.

In the new study, University College London (UCL) researchers said 85% to 90% of the public believes that depression is caused by low serotonin or a chemical imbalance.

Most antidepressants are selective serotonin reuptake inhibitors (SSRIs), and were originally said to work by correcting abnormally low serotonin levels.

Lead author Joanna Moncrieff, a professor of psychiatry at UCL, is a consultant psychiatrist at North East London NHS Foundation Trust (NELFT).

She said: “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, particularly by lower levels or reduced activity of serotonin.

“The popularity of the ‘chemical imbalance’ theory of depression has coincided with a huge increase in the use of antidepressants…

“Thousands of people suffer from side-effects of antidepressants, including the severe withdrawal effects that can occur when people try to stop them, yet prescription rates continue to rise.

The Royal College of Psychiatrists are still encouraging people to not stop taking their medication (PA) (Image: PA)

“We believe this situation has been driven partly by the false belief that depression is due to a chemical imbalance.

“It is high time to inform the public that this belief is not grounded in science.”

What did the study look into?

The review looked at studies involving tens of thousands of people examining serotonin and depression.

One of the findings was that research that compared levels of serotonin and its breakdown products in the blood or brain fluids did not find a difference between people diagnosed with depression and healthy people.

The authors also looked at studies where serotonin levels were artificially lowered in hundreds of people and concluded that lowering serotonin in this way did not produce depression in hundreds of healthy volunteers.

Other studies looked at the effects of stressful life events and found that the more stressful life events a person had experienced, the more likely they were to be depressed, showing the important impact of external events.

According to the research, there is also evidence from other studies that antidepressants may actually induce low serotonin in the long-term.

Prof Moncrieff said: “We do not understand what antidepressants are doing to the brain exactly, and giving people this sort of misinformation prevents them from making an informed decision about whether to take antidepressants or not.”

A spokesman for the Royal College of Psychiatrists said: “Antidepressants will vary in effectiveness for different people, and the reasons for this are complex, which is why it’s important that patient care is based on each individual’s needs and reviewed regularly.

“Continued research into treatments for depression is important to help us better understand how medications work as well as their effectiveness.

“Medication should be available for anyone who needs it. We would not recommend for anyone to stop taking their antidepressants based on this review, and encourage anyone with concerns about their medication to contact their GP.”

The new findings are published in Molecular Psychiatry.