Valdoxan has been compared with placebo (a dummy treatment) in five main short-term studies involving a total of 1,893 adults with major depression. Three of these studies included some patients treated with other antidepressants, either fluoxetine or paroxetine, as an ‘active comparator’. The active comparator groups were included to check that the study was able to measure the effectiveness of medicines in treating depression. The main measure of effectiveness in these five studies was the change in symptoms after six weeks, as measured on a standard scale for depression called the Hamilton Depression Rating Scale (HAM D). In the two studies where no active comparator was used Valdoxan was seen to be more effective than placebo. In the other three studies, which did include an active comparator, there were no differences in scores between the patients taking Valdoxan and those taking placebo. However, no effect of fluoxetine or paroxetine was seen in two of these studies, making the results difficult to interpret.

The company also presented the results of a further study comparing Valdoxan with sertraline (another antidepressant), which showed that Valdoxan was more effective than sertraline, with a reduction in HAM D scores after six weeks..

Two other main studies compared the ability of Valdoxan and placebo to prevent symptoms returning in 706 patients whose depression had already been controlled with Valdoxan. The main measure of effectiveness was the number of patients whose symptoms returned during 24 to 26 weeks of treatment. In the first study, there was no difference between Valdoxan and placebo in preventing symptoms from returning during 26 weeks of treatment. However, the second study showed that symptoms returned in 21% of the patients taking Valdoxan over 24 weeks (34 out of 165), compared with 41% of the patients taking placebo (72 out of 174).