The most common antidepressant does little to relieve symptoms of depression, researchers say.
The largest study of its kind found that most people taking sertraline saw little or no effect on depressive symptoms, such as low mood, in the first six to 12 weeks of taking the drug.
Experts said they were “surprised” by the findings relating to depression, but that it was clear the drugs helped cut anxiety and should continue to be prescribed by GPs.
The study, published in the journal the Lancet Psychiatry and led by University College London (UCL) researchers, was conducted in GP surgeries across England.
It involved 653 people aged 18 to 74 experiencing depressive symptoms, who were split into two groups.
The first group was given a dummy drug for 12 weeks while the second group was given sertraline.
The results showed depressive symptoms were five per cent lower after six weeks in the sertraline group, which was “no convincing evidence” of an effect.
After 12 weeks, there was a 13 per cent reduction – a finding the experts described as “weak”.
But the drug did offer clear benefits on reducing anxiety, with a 21 per cent reduction in symptoms at six weeks and 23 per cent at 12 weeks.
People on sertraline were twice as likely to say they felt better and their overall mental health had improved.
Professor Glyn Lewis, head of division at UCL Psychiatry, who led the study, called for better treatment for depression.
He said: “Antidepressants work but perhaps in a different way to the way we had originally thought.
“They seem to be working on anxiety symptoms first before any smaller, and later, possible effects on depression.
“We definitely need better treatments for depression – we need more research in this area.
“This is an unexpected result. Our primary hypothesis was that it would affect those depressive symptoms at six weeks and we didn’t find that. So it is an unexpected finding.”
The study, funded by the National Institute for Health Research (NIHR), is the largest placebo-controlled trial of an antidepressant which has not been funded by the pharmaceutical industry.
It included people with mild to moderate symptoms of depression for whom there was clinical uncertainty over whether they actually needed treatment.
The researchers said their findings suggest antidepressants may benefit a wider group of people than previously thought, including those who do not meet the criteria for depression or generalised anxiety disorder.
Between 2017 and 2018, 7.3 million people were prescribed antidepressants in England – 17 per cent of the population.
Sertraline is a selective serotonin reuptake inhibitor (SSRI), the most common class of antidepressant.
Professor Helen Stokes-Lampard, chairwoman of the Royal College of GPs, said: “This study gives an interesting insight into how a medication primarily used to treat depression may be improving a patient’s health in other ways in the shorter term by reducing symptoms of anxiety, which is often associated with depression.”
Dr Sameer Jauhar, a senior research fellow and consultant psychiatrist in the NHS, added: “It is not surprising that depressive symptoms did not improve to a great extent, given that only around half the people had a diagnosis of depression.”
Additional reporting by PA.
