New research from a team at the Karolinska Institutet suggests media coverage of studies examining cannabis use as a method for alleviating chronic pain are the recipients of a significant level of positive media coverage, regardless of results.

A systematic review and meta-analysis of 20 studies examining cannabinoids with a double-blind, placebo-controlled design, results of the study demonstrate that although the reductions in pain intensity observed in these studies was significant, media attention of these trials was described as “proportionally high”, with a strong positive bias and no associations observed with clinical outcomes.

“We see that cannabis studies are often described in positive terms in the media regardless of their results,” said lead investigator Filip Gedin, PhD, a postdoctoral researcher at the Department of Clinical Neuroscience, Karolinska Institutet, in a statement. “This is problematic and can influence expectations when it comes to the effects of cannabis therapy on pain. The greater the benefit a treatment is assumed to have, the more potential harms can be tolerated.”

As the decades have gone by since California introduced medical cannabis to the United States, now the majority of states have passed legislation allowing for recreational use. In addition to medically-prescribed cannabis, the popularity of CBD-based products among consumers has also undergone an explosion in recent years. This, combined with growing opioid epidemic, has led to medical cannabis being purported as a panacea of sorts when receiving interest and coverage from large media outlets.

The current research endeavor was led by Gedin and a team of colleagues with the intent of estimating the size of placebo responses in randomize clinical trials comparing cannabinoids to placebo therapy in treatment of pain and whether the magnitude of response was associated with media attention these studies received. With this in mind, investigators designed their study as a systematic review and meta-analysis of data published within the MEDLINE and Embase databases form inception through September 2021.

Limiting their analyses to studies with a double-blind, placebo-controlled design and adult patient populations with clinical pain of any duration, investigators identified 20 studies for inclusion. The investigators’ initial search yielded 922 individual records. Of these, investigators determined 53 met inclusion criteria. From this group, 33 were excluded due to insufficient data for calculating effect size, leaving 20 articles for inclusion in the meta-analysis. These 20 studies included 1459 individuals. This cohort had a mean age of 51 (SD, 7) years, with an age range of 39-62 years, and 56% were female.

For the purpose of analysis, change in pain intensity from before to after treatment, which was measured as bias-corrected standardized mean differences (Hedges g), served as the primary outcome of interest for the study. Investigators pointed out a randomized-effects model was used for pool data and creating effect estimates.

Results of the investigators’ analyses demonstrated pain intensity observed in these studies was associated with a significant reduction in response to placebo, with a moderate to large effect size (mean [SE] Hedges g, 0.64 [0.13]; P <.001). Further analysis demonstrated trials with low risk of bias had greater placebo responses (q1=5.47; I2=87.08; P=.02). Results also suggested they count of media attention and level of dissemination associated with each trial was proportionally high, with a strong positive bias, but was not associated with the clinical outcomes observed in the studies.

“The findings of this systematic review and meta-analysis suggest that placebo responses contribute significantly to pain reduction in cannabinoid clinical trials,” wrote investigators. “The unusually high media attention surrounding cannabinoid trials, with positive reports irrespective of scientific results, may uphold high expectations and shape placebo responses in future trials. This influence may impact the outcome of clinical trials, regulatory decisions, clinical practice, and ultimately patient access to cannabinoids for pain relief.”

This study, “Placebo Response and media attention in randomized clinical trials assessing cannabis-based therapies for pain: A systematic review and meta-analysis,” was published in JAMA Network Open.