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Antidepressants can cause emotional dullness: study

"They become less sensitive to rewards."

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By Alice Clifford via SWNS

Common antidepressants can cause "emotional dullness," taking pleasure out of everyday experiences, a new study reveals.

It's estimated that around 37 million Americans take antidepressants.

A widely-used class of antidepressants, particularly used for persistent or severe cases, is selective serotonin reuptake inhibitors (SSRIs).

These drugs target serotonin, a chemical that carries messages between nerve cells in the brain and has been dubbed the ‘pleasure chemical.'

One of the widely reported side effects of SSRIs is "blunting," where patients feel emotionally dull and stop finding things as pleasurable as they used to.

Between 40 to 60 percent of patients taking SSRIs are believed to experience this side effect.

Antidepressants can also have an effect on sex.

People who take escitalopram, one of the best-tolerated SSRIs, often report that they struggle to reach orgasm when having sex.

For the study, 66 healthy volunteers were recruited. Out of the group, 32 were given escitalopram, while the other 34 were given a placebo.

They took the drug or placebo for at least 21 days.

During this time, they completed a comprehensive set of questionnaires and were given a series of tests assessing their cognitive functions.

These included learning, inhibition, executive function, reinforcement behavior, and decision-making.

The team found no significant difference when it came to attention and memory.

There were also no differences in most tests that assessed cognitive functions that involved emotions.

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However, taking the drug did reduce participants’ sensitivity to rewards and their ability to respond to them during two of the tasks.

Those taking escitalopram found it harder to learn from feedback from their actions and environment.

They were less likely to use positive and negative feedback to guide their learning. These results were clear during a reversal test.

In this task, a participant was shown two stimuli, named A and B.

If they chose A, then four out of five times they would get a reward but if they chose B they would only receive a reward one time out of five.

The volunteers were not told this rule, but they would have to learn it themselves.

At some point in the experiment, the probabilities would switch meaning the participants would need to learn the new rule.

Those taking the drug found it much harder to use positive and negative feedback to guide their learning.

Professor Barbara Sahakian, from the Department of Psychiatry at the University of Cambridge, and senior author, said: “Emotional blunting is a common side effect of SSRI antidepressants.

“In a way, this may be in part how they work – they take away some of the emotional pain that people who experience depression feel, but, unfortunately, it seems that they also take away some of the enjoyment.

“From our study, we can now see that this is because they become less sensitive to rewards, which provide important feedback.”

Dr. Christelle Langley, from the Department of Psychiatry, and senior author, added: “Our findings provide important evidence for the role of serotonin in reinforcement learning.

"We are following this work up with a study examining neuroimaging data to understand how escitalopram affects the brain during reward learning.”

The results of the study are published in the journal Neuropsychopharmacology.

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