In a small-scale study, escitalopram, a commonly prescribed antidepressant, reduced subjects’ sensitivity to pleasurable experiences.
People taking antidepressants often experience that their positive feelings are diluted as well. That this unwanted weakening occurs is now proven by neuroscientist Christelle Langley from the University of Cambridge.
The most commonly prescribed antidepressants belong to the class of selective serotonin reuptake inhibitors (SSRIs). They are thought to increase levels of serotonin, a neurotransmitter in the brain known as the “happiness hormone.” But why that can improve mood is not fully known.
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About half of people taking antidepressants experience an involuntary diminution of both positive and negative feelings. “They say they don’t feel much,” says neuropsychiatrist Barbara Sahakianwho was involved in the research.
Reward test
Whether this is due to antidepressants is difficult to investigate. Also depression itself can cause a loss of pleasure in activities that someone previously enjoyed. That is why Langley and her colleagues investigated the dampening effect of SSRIs in test subjects who had no mental health problems.
The team gave either the commonly prescribed SSRI escitalopram or a placebo to 66 subjects without depression. After three weeks, the subjects performed various tasks that tested memory and learning ability.
One of those tasks measured how well the subjects could learn when rewards were given. They had to choose between two stimuli. Through trial and error, they learned that one stimulus led to the reward more often than the other. Subsequently, the probability of reward switched for each stimulus, and the subjects had to relearn the system.
The subjects who received escitalopram were 23 percent less sensitive to the chance change than those who received the placebo. This was evident from the speed with which they mastered the new system. Other trials showed that the drug had no effect on other cognitive abilities.
Reluctance in doctors
The finding suggests that SSRIs dampen people’s sensitivity to rewards or other pleasurable experiences, says Sahakian. But she adds that the medication can also lessen the intensity of negative feelings, which is desirable. “I hope this doesn’t make doctors more hesitant to prescribe antidepressants,” she says. ‘They are very important medicines. I hope that doctors will talk more quickly with their patients about possible side effects.’
“Why antidepressants weaken some people’s emotions is a very important question,” says neuroscientist Catherine Harmer from the University of Oxford. “I don’t think these findings explain why some people experience that.” She does say that the research is a step forward in developing new drugs that do not weaken feelings. The study, she says, would have been more useful if the subjects had also been asked whether they experienced weakened emotions.
