According to scientists, widely prescribed antidepressants can make patients less sensitive to rewards – affecting an important behavioral learning process that can lead to emotional dullness.
Researchers have found that selective serotonin reuptake inhibitors, or SSRIs, can affect reinforcement learning, which allows people to learn from their actions and their environment.
These drugs work by targeting the body’s “feel-good” chemical known as serotonin, which carries messages between nerve cells in the brain.
A commonly reported SSRI side effect is “blinding”, which patients say feel emotionally dulled and unable to respond with the same level of enjoyment they would normally.
The experts said their findings, published in the journal Neuropsychopharmacology, show how serotonin affects reinforcement learning.
Professor Barbara Sahakian, from Cambridge University’s department of psychiatry, one of the senior authors of the study, said: “Emotional atrophy is a common side effect of SSRI antidepressants.
“In a way, they may partly work that way – they get some of the emotional pain that people with depression feel, but unfortunately, they apparently also get some of the pleasure.
“From our study, we can now see that this is due to them becoming less sensitive to rewards that provide important feedback.”
The researchers recruited 66 volunteers to participate in the experiment; 32 of these were given escitalopram and the remainder were given placebo.
All participants completed a comprehensive self-report questionnaire after 21 days and were tested on cognitive functions, including learning, inhibition, executive function, reinforcement behavior, and decision making.
The results showed reduced reinforcement sensitivity in the two tasks for the escitalopram group compared to placebo.
Participants who took escitalopram were less likely to use positive and negative feedback to guide their learning of the task, compared to those who took a placebo, the researchers said.
The team added that this suggests that the drug affects their sensitivity to rewards and their ability to respond accordingly.
But other experts have warned that patients using SSRI drugs based on this research should not stop taking them.
Commenting on behalf of the Royal College of Psychiatrists, Professor Carmine Pariante, who was not involved in the research, said: “This is an interesting and well done study in healthy subjects, but it does not change our understanding of antidepressants.
“People who are depressed may have trouble feeling positive emotions such as happiness, making it difficult to distinguish between the effects of the condition and the effects of medications.
“Antidepressants can help people recover by reducing negative emotions.”
He added that antidepressants are an effective form of treatment for people experiencing depression, which has a negative impact on their quality of life and where other treatments, such as talking therapies, have not worked.
Professor Pariante said: “Practitioners should always discuss the potential risks and benefits of taking antidepressants with their patients because we know their effects can vary from person to person.
“Clinicians should regularly review their use to ensure they are still needed.
“Based on this research, we do not recommend anyone stop taking their antidepressants, and we do not encourage anyone with concerns about their medication to consult their GP.”
NHS figures released in July showed 8.3 million patients in the UK were taking antidepressants in 2021/22; this is a 6% increase from 7.9 million the previous year.
Reviewing nearly 1,000 existing studies published in JAMA Psychiatry in 2019, the research concluded that antidepressants are generally safe.