Why antidepressants can dull both negative and positive emotions

Why antidepressants can dull both negative and positive emotions

Escitalopram, a commonly prescribed antidepressant, reduced people’s sensitivity to rewarding experiences in a small trial

Health


23 January 2023

The antidepressant escitalopram may reduce the ability to enjoy rewarding experiences

The antidepressant escitalopram can reduce people’s sensitivity to rewarding experiences

GIPHOTOSTOCK/SCIENCE PHOTO LIBRARY

An unwanted flattening of all emotions is one of the most common side effects of antidepressants, and now we know more about why it can happen.

The most commonly used types of antidepressants belong to a class called selective serotonin reuptake inhibitors (SSRIs). They are thought to work by increasing levels of serotonin, a brain chemical, although why this may improve our mood is not clear.

Up to half of people who take antidepressants experience an unwanted decrease in positive and negative emotions. “They talk about not feeling much,” says Barbara Sahakian of Cambridge University.

Depression itself also often causes a lack of pleasure in activities a person once enjoyed. Therefore, Sahakian and his colleagues investigated the emotion-dampening effect of an SSRI in people without the mental health condition.

The researchers administered a commonly prescribed SSRI called escitalopram or placebo pills to 66 people without depression. After three weeks, the participants carried out a variety of tasks related to memory and learning.

One task measured how well they learned from rewards, with people repeatedly having to choose between two stimuli. Through trial and error, they generally learned that one stimulus led to a reward more often than the other. Then the odds of a reward for each stimulus would change, and the participants had to learn this new system.

Participants taking the antidepressant were 23 percent less sensitive to stimulus change than those taking the placebo, as measured by how quickly their stimulus selections changed. Other tests showed that the drug did not reduce their cognitive abilities in any other way.

The finding suggests that SSRIs reduce people’s sensitivity to rewards or other pleasurable experiences, Sahakian says. But medications can also dull the intensity of negative feelings, which can be helpful, he adds.

“I hope this doesn’t make doctors more cautious about prescribing antidepressants, as they are extremely important drugs,” he says. “I hope it gets doctors to have a discussion with patients about possible side effects.”

“Why antidepressants cause emotional blunting in a subset of people is a really important question,” says Catherine Harmer of the University of Oxford. “I don’t think this result explains why people have this effect, but it may be a marker for it, which could be useful when we get to developing new treatments that don’t.”

Harmer says the study would have been more useful if the participants had also been asked if they experienced blunted emotions while taking the antidepressant.

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