Patients taking antidepressants may become less sensitive to rewards, study

Widely prescribed antidepressants may make patients less sensitive to rewards – by affecting a key behavioral learning process that researchers say can lead to emotional dullness.

Researchers have found that selective serotonin reuptake inhibitors, or SSRIs, can affect reinforcement learning, which allows people to learn from their actions and environment.

These drugs work by targeting the “feel good” chemical known as serotonin, which carries messages between nerve cells in the brain.

A widely reported side effect of SSRIs is “dulling”, in which patients say they feel emotionally dull and unable to respond with the same level of pleasure as normal.

The experts said their findings, published in the journal Neuropsychopharmacology, show how serotonin influences reinforcement learning.

Professor Barbara Sahakian, from the University of Cambridge’s Department of Psychiatry, who is the study’s lead author, said: “Emotional blunting is a common side effect of SSRI antidepressants.

“In some ways, this may be partly due to how they work – they remove some of the emotional pain suffered by people suffering from depression, but unfortunately they also seem to take away some of the pleasure.

“Our research suggests that this is because they become less sensitive to rewards that provide important feedback.”

The researchers recruited 66 volunteers to take part in the experiment, 32 of whom received escitalopram and the rest a placebo.

All participants completed an extensive set of self-report questionnaires after 21 days and were tested on cognitive functions including learning, inhibition, executive functions, reinforcement behaviors and decision making.

The results showed that for two tasks, the escitalopram group had a reduced sensitivity to reinforcement compared to placebo.

The researchers found that participants taking escitalopram were less likely to use positive and negative feedback to guide task learning compared to those taking a placebo.

This suggests that the drug affected their sensitivity to rewards and their ability to respond appropriately, the team added.

But other experts warn that patients taking SSRIs should not stop taking them based on these studies.

Commenting on behalf of the Royal College of Psychiatrists, Professor Carmine Pariante, who was not involved in the study, said: “This is an interesting and well-conducted study in healthy people, but it does not change our understanding of antidepressants.

“People with depression may find it difficult to feel positive emotions, such as happiness, making it difficult to distinguish between the effects of illness and the effects of medication.

“By reducing negative feelings, antidepressants can help people recover.”

He added that antidepressants are an effective form of treatment for people experiencing depression that has a detrimental effect on their quality of life and where other treatments, such as talk therapies, have failed.

Professor Pariante said: “Practitioners should always discuss the potential risks and benefits of taking antidepressants with their patients, as we know that their effectiveness can vary from person to person.

“Clinicians should also review their use regularly to ensure they are still needed.

“We are not advising anyone to stop taking antidepressants based on this study and we encourage anyone with concerns about their medication to contact their GP.”

NHS figures released in July showed that 8.3 million patients received antidepressants in England in 2021/22, up 6% from 7.9 million the previous year.

In 2019, a study of about 1,000 existing studies published in JAMA Psychiatry found that antidepressants are generally safe.

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