By Pat Anson, PNN Editor

The placebo effect is responsible for much of the pain relief experienced by participants in clinical trials of cannabis, according to new analysis that also found a “strong positive bias” in media coverage of the studies.

Researchers at the Karolinska Institute in Sweden analyzed the results of 20 placebo-controlled studies of cannabis products involving almost 1,500 people with chronic pain conditions. The cannabis products were administered as pills, sprays, oils, smoke or vapor; and most of the studies were conducted in the United States, UK or Canada.

Researchers found that many participants reported significant pain relief, but there were no differences in pain reduction between those who used cannabis products and those who used a placebo, a sham treatment that should have no effect.

“There is a distinct and clinically relevant placebo response in studies of cannabis for pain,” says Filip Gedin, PhD, a researcher in the Department of Clinical Neuroscience at Karolinska and lead author of the study published in JAMA Network Open.

Gedin and his colleagues also examined coverage the 20 studies received in the news media using Altmetric, a method of evaluating mentions in the media as either positive, negative or neutral. They did not identify the publishers of the 136 news articles that were analyzed or provide any examples of their coverage.

Researchers found that the cannabis studies received much greater media attention than other clinical studies and tended to be more positive, regardless of what the studies’ outcomes actually were. The media coverage of cannabis was so positive, in fact, that researchers wonder if it might influence findings in future studies.  

“The positive media attention and wide dissemination may uphold high expectations and shape placebo responses in future trials, which has the potential to affect the outcome of clinical trials, regulatory decisions, clinical practice, and ultimately patient access to cannabinoids for pain relief,” Gedin wrote. “We therefore consider this question to be of high importance, as the positive reporting toward cannabinoids regardless of study quality and effect size may subsequently lead to increased expectations that may ultimately influence the outcomes in clinical trials.”

The placebo effect is a well-documented but poorly understood condition in which a patient responds to a sham drug or treatment that should have no therapeutic value. A 2018 study at Northwestern University, for example, found that about half of patients who took a sugar pill they thought was an analgesic had a 30% reduction in pain – a level considered good enough for an actual painkiller.    

In another study, researchers identified some participants as “placebo responders” who are more likely to respond to a sugar pill because their brains react differently – which may explain why some patients find a medication effective and others don’t.    

Whatever the cause, researchers at the Karolinska Institute say more effort is needed to understand the placebo effect and how media coverage could make it even more potent.

“We cannot say with 100% certainty that media coverage is responsible for the high placebo response observed in our review,” Gedin wrote in an op/ed published in The Conversation.

“But given placebos were shown to be just as good as cannabis for managing pain, our results show just how important it is to think about the placebo effect and how it can be influenced by external factors – such as media coverage. For treatments, such as cannabinoids, that receive a lot of media attention, we need to be extra rigorous in our clinical trials.”