The theory that antidepressant drugs, such as the SSRIs, do not work, which has gained considerable international media attention, has been rebutted by an analysis of clinical trials by the Sahlgrenska Academy.
According to the challenged hypothesis, the fact that many people medicating with antidepressants regard themselves as improved may be attributed to a placebo effect, ( that someone who expects to be improved by a medication often also feels improved, 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 clinical trials where patients have been treated with an SSRI or with ineffective placebo pills, and where 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 will make the patient understand that he or she has not been given placebo, hence 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. Thus, so far, it has never been investigated whether individuals in clinical trials experiencing side effects from antidepressant medication, and for this reason may have guessed that they have not received placebo, also respond more favorably to treatment than those without side effects.
In order to examine the “placebo breaking the blind” theory, a research group at the Sahlgrenska Academy in Gothenburg, Sweden, has now analysed 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, shows 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 theory that antidepressants outperform placebo merely by means of side effects making the patient realising that he or she has not been given placebo, and herby enhancing the expectancy of improvement, may hence be rejected.
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. They suggest that the frequent questioning of these drugs in media is unjustified and may make depressed patients refrain from effective treatment.
It has been suggested that the superiority of antidepressants over placebo in controlled trials is merely a consequence of side effects enhancing the expectation of improvement by making the patient realize that he/she is not on placebo. We explored this hypothesis in a patient-level post hoc-analysis including all industry-sponsored, Food and Drug Administration-registered placebo-controlled trials of citalopram or paroxetine in adult major depression that used the Hamilton Depression Rating Scale (HDRS) and included a week 6 symptom assessment (n=15). The primary analyses, which compared completers on active treatment without early adverse events to completers on placebo (with or without adverse events) with respect to reduction in the HDRS depressed mood item showed larger symptom reduction in patients given active treatment, the effect sizes being 0.48 for citalopram and 0.33 for paroxetine. In actively treated subjects reporting early adverse events, who also outperformed those given placebo, the severity of the adverse events did not predict response. Several sensitivity analyses, for example, including (i) those using change of the sum of all HDRS-17 items as effect parameter, (ii) those excluding all subjects with adverse events (that is, also those on placebo) and (iii) those based on the intention-to-treat population, were all in line with the primary analyses. The finding that both paroxetine and citalopram are clearly superior to placebo also when not producing adverse events, as well as the lack of association between adverse event severity and response, argue against the theory that antidepressants outperform placebo solely or largely because of their side effects.
F Hieronymus, A Lisinski, S Nilsson, E Eriksson