There remains great debate on the efficacy of antidepressant medications. While these medications, namely selective serotonin reuptake inhibitors (SSRIs), are widely prescribed, approximately half of company-sponsored studies fail to find statistical differences between taking an SSRI and a placebo. So researchers from the Sahlgrenska Academy in Sweden set out to see if this has to do with how efficacy is measured.

The Hamilton depression rating scale (HDRS) has been used to measure the severity of depression in patients already diagnosed with the illness since the late 50s, researchers cited; there are 17 different symptoms patients can either receive a score between 0 and 2 or 0 and 4. Most antidepressant trials based efficacy off the decrease in the total score of the HDRS scale. Yet, those opposed to the scale have a problem with how multidimensional it is, "indicating that relevant improvement in one domain of symptoms may be masked."

"In order to measure the antidepressant effect, the pharmaceutical companies have unwisely assessed the reduction in the sum score for a large number of symptoms listed on a rating scale," Elias Eriksson, lead researcher and pharmacologist, said in a press release. "However, the sensitivity of this instrument is markedly marred by the fact that many of these symptoms occur also in subjects without depression, while others are absent also in many depressed patients. For this and other reasons, the usefulness of this rating scale, which was constructed already during the 1950s, has since long been questioned."

Instead, Eriksson and his team investigated what happens if the effects treatment has on depressive mood is used as a measure of efficacy. By study’s end, the team analyzed 32 drug-placebo comparisons involving nearly 7,000 adults with major depression. The results showed only three out of 32 comparisons were negative when depressed mood was used as an effect parameter. Put it another way: 29 out of 32 comparisons showed a significant difference in favor of the SSRIs.

“Our conclusion is that the questioning of the antidepressant efficacy of SSRIs is to a large extent based on an unfortunate misinterpretation of the available data,” Eriksson said. “The truth is that the scientific support for these drugs exerting an antidepressant impact is very robust across studies.”

The study may suggest it is “reasonable” to say the HDRS should no longer be the primary effect parameter, but more research needs to be done in antidepressant trials on the sensitivity of using alternative scales to measure the severity of the illness.

Source: Hieronymus F, Emilsson JF, Nilsson S, and Eriksson E. Consistent superiority of selective serotonin reuptake inhibitors over placebo in reducing depressed mood in patients with major depression. Molecular Psychiatry. 2015.