In a clinical trial, the participants who took a placebo suffered from adverse events. The study has data from 1,271 randomized trials and 250,726 trial participants. Half of the participants taking a placebo, which is an inert sugar pill, was reported to be suffering from abdominal pain and anorexia to burning, chest pain, fatigue, and even death after consuming it. Moreover, 1 in 20 people who were taking placebos dropped out of their trials because of more serious adverse events.
The question arises how a sugar pill could cause harm. The researchers stated that it was a mistaken belief about the cause of the event. A participant in a trial may have a stomach- ache for any reason that is not related to the clinical trial. But, as they are in trial intervention, they think that the trial intervention caused the ache, misattributing the cause. For example, a study of aspirin or sulfinpyrazone was performed on patients in a randomized trial for treating unstable angina. It was found that gastrointestinal adverse events were six times more likely to withdraw from the study due to reported gastrointestinal adverse events.
At times, the way patients are warned about adverse events makes them believe that they would face an adverse event. Therefore, misattributions are hard to avoid as it is difficult for someone in a trial to know whether a symptom like a stomach-ache is caused by the trial intervention or the state that led them to enter the trial.
To reduce the harm caused by negative expectations, the patients are informed that a new treatment is safe for 90 percent, which has the same information that it causes adverse events like headaches in ten percent of patients. Guidance for informing trial participants about trial intervention gives a negative impact, in a way that does not produce a negative placebo effect. The information provided to participants often fails to meet their needs, as they are presented in a way that they sometimes find difficult to understand.
Ongoing researches are looking for ways to keep patients in trials informed about the benefits and harms of participating in trials in the most feasible way.