Expectations and Dopamine Can Affect Outcome of SSRI Antidepressant Treatment

Summary: The placebo effect combined with dopamine levels can determine whether symptoms of depression and social anxiety will improve in patients prescribed SSRI antidepressants. Researchers found the positive effect of the medications was four times higher in patients with high expectations the treatment would work compared to those with lower expectations.

Source: Uppsala University

Levels of dopamine and the placebo effect can determine whether patients with social anxieties improve when treated with SSRIs.

A new study shows the effect was four times higher for patients with high expectations of the medication compared with patients with low expectations. This was true even though the groups received the same medical treatment.

Although SSRIs influence levels of serotonin in the brain, the effects on dopamine had the greatest impact for improvement.

Selective serotonin reuptake inhibitors (SSRIs) are an established and effective medication for treating depression and anxiety. The placebo effect, where the positive effects of a treatment can increase when a patient expects to be helped, is a well-known phenomenon.

The effect can be significant, and it is unclear how much of the improvement results from expectations of the SSRI treatment. It is also unclear whether the expectations use the same mechanism in the brain as SSRI medications (the inhibiting of the transporter protein for serotonin) or whether other neurotransmitters are involved. The new study points to the transporter protein for dopamine being the key.

Researchers at Uppsala University confirmed in a study on social anxiety published in Translational Psychiatry that the placebo effect had a major impact on the anti-anxiety effect of the SSRI drug escitalopram. The surprising finding in the study was that the improvement after SSRI treatment can largely be linked to effects on dopamine rather than to the serotonin transporters.

In the study, all the participants were treated with the same clinical dose of escitalopram for nine weeks, but they had different expectations. Half received accurate information about the drug and its effectiveness, while a cover story was used for the other half. Participants in the second group were told that the drug was an ‘active placebo’ that causes similar side effects as SSRIs but was not expected to alleviate their social anxiety.

This shows a colorful brain
The surprising finding in the study was that the improvement after SSRI treatment can largely be linked to effects on dopamine rather than to the serotonin transporters. Image is in the public domain

“The results showed that almost four times as many patients responded to the treatment when correct information about the drug was given. This is consistent with previous research showing that expectations affect treatment outcome,” says researcher Olof Hjorth.

Positron emission tomography (PET) brain scanning showed that the SSRI drug had the same effect on serotonin and blocked about 80 percent of serotonin transporters in both groups. This was true even for the group that had low expectations and did not improve.

“This indicates that the pharmacological effect was identical in both groups and that this cannot explain why correct information gave better treatment results. So, inhibiting serotonin transporters is insufficient for achieving good clinical relief from social anxiety using SSRI drugs.”

When assessing the transporter protein for dopamine after treatment, however, a clear difference between the groups was observed. Participants who began the treatment knowing that it was an effective drug showed a reduced availability of dopamine transporters in the striatum, a part of the cerebrum, while the opposite was true in the group that was given the cover story. One explanation may be that expectations affected the release of dopamine in the brain’s reward pathways. This may have led to differences in the two groups in the proportion of dopamine transporters available after treatment.

“The results indicate that positive expectations arising in the relationship between doctor and patient affect dopamine and enhance the effect of SSRI treatment,” says Professor Tomas Furmark, who led the study.

About this psychopharmacology research news

Author: Press Office
Source: Uppsala University
Contact: Press Office – Uppsala University
Image: The image is in the public domain

Original Research: Open access.
Expectancy effects on serotonin and dopamine transporters during SSRI treatment of social anxiety disorder: a randomized clinical trial” by Olof R. Hjorth et al. Translational Psychiatry


Expectancy effects on serotonin and dopamine transporters during SSRI treatment of social anxiety disorder: a randomized clinical trial

It has been extensively debated whether selective serotonin reuptake inhibitors (SSRIs) are more efficacious than placebo in affective disorders, and it is not fully understood how SSRIs exert their beneficial effects. Along with serotonin transporter blockade, altered dopamine signaling and psychological factors may contribute.

In this randomized clinical trial of participants with social anxiety disorder (SAD) we investigated how manipulation of verbally-induced expectancies, vital for placebo response, affect brain monoamine transporters and symptom improvement during SSRI treatment.

Twenty-seven participants with SAD (17 men, 10 women), were randomized, to 9 weeks of overt or covert treatment with escitalopram 20 mg. The overt group received correct treatment information whereas the covert group was treated deceptively with escitalopram, described as an active placebo in a cover story.

Before and after treatment, patients underwent positron emission tomography (PET) assessments with the [11C]DASB and [11C]PE2I radiotracers, probing brain serotonin (SERT) and dopamine (DAT) transporters. SAD symptoms were measured by the Liebowitz Social Anxiety Scale. Overt was superior to covert SSRI treatment, resulting in almost a fourfold higher rate of responders.

PET results showed that SERT occupancy after treatment was unrelated to anxiety reduction and equally high in both groups. In contrast, DAT binding decreased in the right putamen, pallidum, and the left thalamus with overt SSRI treatment, and increased with covert treatment, resulting in significant group differences. DAT binding potential changes in these regions correlated negatively with symptom improvement.

Findings support that the anxiolytic effects of SSRIs involve psychological factors contingent on dopaminergic neurotransmission while serotonin transporter blockade alone is insufficient for clinical response.

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