A 21-year-old woman presents to a psychiatrist for an initial intake appointment. She reports decreased mood, decreased appetite, anhedonia, and difficulty concentrating for the past 2 weeks. Past medical history is significant for major depressive disorder (MDD), which has previously been treated with adequate trials of various selective serotonin reuptake inhibitors (SSRIs). She states previous treatment “worked for a while, but then it just stopped working.” Her most recent episode of depressive symptoms was 6 months ago. She does not use any illicit substances, and her screening laboratory tests are unremarkable. The patient states she recently saw a commercial advertising a new antidepressant and asks if adding this drug to her current medications would prevent another MDD relapse. The data from a randomized controlled trial in which this new drug was used as an adjunct demonstrated that 15 percent of patients relapsed within 1 year, compared to 30 percent of patients in the placebo group.
Which of the following statements is most likely correct when comparing the protocol for the placebo group and the treatment group in this clinical trial?
E) The placebo group received only their pre-existing MDD regimen
When it is feasible to do so, the placebo in a trial receives no treatment, essentially serving as a negative control. However, it is unethical to withhold treatment when doing so poses harm to study participants. The most likely design for this clinical trial was a placebo arm that continued to receive their current treatment for MDD but did not have the new drug added to that regimen.
Answer choice A: The placebo group and treatment group received an equal dose of the new drug, is incorrect. If this were true, there would be no difference in the protocol for the treatment and control groups. That would make a clinical trial futile, since there would be no independent variable manipulated.
Answer choice B: The placebo group received a higher dose of the new drug than the treatment group, is incorrect. This answer choice is very counterintuitive. If a clinical trial were testing if a lower dose of a certain drug than currently recommended could maintain efficacy with fewer side effects, then perhaps the placebo group would receive standard of care (high dose) and the trial group would receive a lower dose.
Answer choice C: The placebo group received a lower dose of the new drug than the treatment group, is incorrect. It is feasible that future studies might be designed as dose-response studies to determine optimal dosing regimens of the new drug. In that case, however, there would be multiple treatment arms, each receiving a different dose. The placebo group would still not be receiving the new drug.
Answer choice D: The placebo group received no treatment for their MDD, is incorrect. As stated above, it is unethical to completely withhold treatment.
Key Learning Point
Interpreting data from clinical trials is an important part of evidence-based medicine. Clinical trials test a hypothesis by choosing a relevant outcome, quantifying that outcome for a trial (experimental) and control (placebo) group, and comparing the data between those groups. The trial group receives the new treatment being tested, which may be a different drug altogether or simply a different dosing regimen than the standard of care. The placebo, contrastingly, serves as a baseline against which to compare the results from the trial group. Although the placebo group does not receive the new treatment being tested, they still receive standard of care treatment.
