Escitalopram, a commonly prescribed antidepressant, reduced people’s sensitivity to rewarding experiences in a small trial
23 January 2023
One of the most common side effects of antidepressants is an unwanted numbing of all the emotions – 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). These are thought to work by increasing levels of the brain chemical serotonin, although it is not clear why this can improve our mood.
Up to half of people who take antidepressants experience unwanted relief from both positive and negative emotions. “They talk about not feeling much,” says Barbara Sahakian at the University of Cambridge.
Depression itself often results in a lack of pleasure in activities that a person once enjoyed. So Sahakian and her colleagues investigated the mood dampening effect of SSRIs in people without the mental health condition.
The researchers gave 66 people without depression a commonly prescribed SSRI called escitalopram pills or a placebo. After three weeks, the participants performed a range of tasks related to memory and learning.
One task measured how well they learned from a reward, and people had to repeatedly choose between two stimuli. Through trial and error, they generally learned that one stimulus elicited a reward more often than the other. Then the reward probabilities for each stimulus would change and the participants had to learn this new system.
Participants who took the antidepressant were 23 percent less sensitive to the stimulus switch than participants who took the placebo, as measured by how quickly they changed their stimulus preferences. Other tests showed that the medicine did not reduce their cognitive abilities in other ways.
The finding suggests that SSRIs reduce people’s sensitivity to rewards or other pleasurable experiences, Sahakian says. But the medications can also moderate the intensity of negative emotions, which can be helpful, she says.
“I hope this doesn’t make doctors more cautious about prescribing antidepressants because they are very important drugs,” she says. “Hopefully it would encourage doctors to discuss potential side effects with patients.”
“Why antidepressants cause emotional blunting in a subset of people is a really important question,” says Catherine Harmer at the University of Oxford. “I don’t think this finding explains why people have this effect, but it could be a sign of it, which could be useful when we come to develop new treatments that don’t have it.”
Harmer says the study would have been more useful if the participants had also been asked if they experienced mild feelings while taking the antidepressant.
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