Why antidepressants can dampen negative and positive emotions

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

Through Claire Wilson

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). These are believed to work by increasing levels of the brain chemical serotonin, although why it may improve our mood is unclear.

Up to half of people taking antidepressants experience an unwanted dampening of positive and negative emotions. “They talk about not feeling much,” says Barbara Sahakyan at the University of Cambridge.

Depression itself often causes a lack of pleasure in activities that a person once enjoyed. Sahakian and his colleagues therefore studied the emotion dampening effect of an SSRI in people without Mental Health condition.

The researchers gave either a commonly prescribed SSRI called escitalopram or placebo pills to 66 people without depression. After three weeks, participants performed a series of tasks involving Memory and learning.

One task measured how well they learned about rewards, with people repeatedly having to choose between two stimuli. Through trial and error, they usually learned that one stimulus more often resulted in a reward than another. Then the probabilities of a reward for each stimulus changed and the participants had to learn this new system.

Participants who took the antidepressant were 23% less responsive to changing stimuli than those who took the placebo, as measured by how quickly they changed their stimulus selections. Further 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 lessen the intensity of negative feelings, which can be helpful, she adds.

“I hope this doesn’t make doctors more cautious about prescribing antidepressants, because these are extremely important drugs,” she says. “Hopefully this will get doctors talking to patients about potential side effects.”

“Why antidepressants cause emotional blunting in a subset of people is a really important question,” says Catherine Harmer at Oxford University. “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 have it.”

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