A new Swedish study rebukes the assertion that the benefit of antidepressant drugs, especially selective serotonin reuptake inhibitors (SSRIs), are a result of the placebo effect.
The theory had gained considerable attention in international media, including Newsweek and the CBS broadcast 60 minutes.
According to the challenged hypothesis, the fact that many people medicating with antidepressants regard themselves as improved was because they expected to be improved by the medication — even if the medicine lacks actual effect.
However, if SSRIs had indeed acted merely by means of a placebo effect, these drugs should not outperform actual placebo in double blind clinical trials. These trials or experiments, measure depression relief when patients have been treated with an SSRI or with a placebo pill. The study design means that neither the physician nor the patient knows which treatment the patient has been given until the study is over.
To explain why antidepressants in such trials nevertheless often cause greater symptom relief than placebo, it has been suggested that SSRI-induced side effects influence a patient’s perception. That is, the side-effects inform a person that they have not been given placebo, thereby enhancing his or her belief of having been given an effective treatment.
The beneficial effect of SSRIs that has been shown in many studies should thus, according to this theory, not be due to the fact that these drugs exert a specific biochemical antidepressant action in the brain, but that the side effects of the drugs enhance a psychological placebo effect.
This theory has been widely disseminated despite the fact that there has never been any robust scientific support for it.
In order to examine the “placebo breaking the blind” theory, a research group at the Sahlgrenska Academy in Gothenburg, Sweden, analyzed data from the clinical trials that were once undertaken to establish the antidepressant efficacy of two of the most commonly used SSRIs, paroxetine, and citalopram.
The analysis, which comprised a total of 3,344 patients, showed that the two studied drugs are clearly superior to placebo with respect to antidepressant efficacy also in patients who have not experienced any side effects.
The researchers conclude that this study, as well as other recent reports from the same group, provides strong support for the assumption that SSRIs exert a specific antidepressant effect.
The finding shows that the benefit of antidepressants is real, and not a function of a placebo interpretation.
Investigators warn that the frequent questioning of these drugs in media is unjustified and may make depressed patients refrain from effective treatment.
Source: University of Gothenburg