Some people suffering from cancer and other chronic illnesses turn to marijuana to alleviate their suffering, but much of that relief may come simply from believing that marijuana will help, according to a new study.
In research, the tendency to have positive expectations that a bogus pill, procedure, or treatment will help is called the placebo effect.
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“The placebo response was 67% of the pain relief associated with genuine cannabinoids,” said lead author Karin Jensen, associate professor and research group leader in the pain neuroimaging laboratory at Karolinska Institutet, Stockholm area.
“Factors such as patients’ expectations of relief likely play a role in the analgesic effects associated with cannabis-based treatments,” Jensen said in an email.
The results of the recent study, published Nov. 28 in the journal JAMA Network Open, echo those of another large 2021 review of available evidence by the International Association for the Study of Pain. Based on these findings, the association issued a statement against the use of marijuana for pain.
“There is insufficient high-quality human clinical safety and efficacy evidence to allow the IASP to endorse the general use of cannabis and cannabinoids for pain at this time,” the association said at the time.
A 2020 study, for example, found that using marijuana before entering the hospital for a surgical procedure significantly worsened pain during recovery. People who previously used marijuana also needed more anesthesia during surgery, and anesthesia can be risky for some people, such as older adults or those with chronic conditions such as diabetes. Marijuana users also needed more opioids during recovery.
Another 2020 analysis of six randomized controlled trials that included nearly 1,500 cancer patients in the UK and Europe found no change in mean pain intensity between people who used cannabis and those who took dummy pills. In the study, some cannabis users experienced side effects severe enough to cause them to drop out of the studies. Reported side effects have included dizziness, nausea, vomiting, fatigue, and drowsiness.
“I think we set patients up to expect a certain type of outcome,” said experimental psychologist Harriet de Wit, a professor of psychiatry and behavioral science at the University of Chicago who studies the placebo effect.
“No doubt some people are hoping to get the active drug and will experience some of these positive results. This is true with antidepressants; it’s true with painkillers,” said de Wit, who was not involved in the new cannabis study.
“It’s an interesting and very real phenomenon,” he added. “It’s certainly not ‘all in your head.’ And yet, there are some brain circuits involved in creating these thoughts and expectations.”
The sugar pill effect
The placebo effect was first discovered in the late 1700’s. It soon became the basis of many of the horrific treatments doctors at the time used, such as bleeding, blisters, and leeches, to name a few mentioned in a 1990 newspaper article.
“The enormous power of the placebo helps explain why physicians have continued to be useful, respected, and highly honored members of society despite the painful, disgusting, unscientific, and often dangerous treatments they have prescribed,” wrote lead author Charmane Eastman, director founder of Biological Rhythms Research. Laboratory at Rush University Medical Center in Chicago.
In modern clinical trials, researchers typically give the tested drug to half of the study participants, while the so-called sugar pill goes to an equally matched group of people. Neither group should know which pill they received. If it’s a double-blind study, not even the researchers know which pill the participants swallowed.
But sometimes people can tell if the pill produces an effect that can be felt, like the effect of marijuana. And even if they don’t know it, people have been known to believe they actually got the trial dose.
In fact, the upbeat attitude generated by a placebo can be powerful enough to dramatically affect study results. For example, the placebo effect may account for 50% to 75% of positive results found in antidepressant drug trials, according to a 2002 study.
Partly to combat this effect, scientists do not consider the results of a study to be significant until they surpass chance.
setting expectations
The new research examined 20 studies using cannabis for pain management in more than 1,450 people ages 33 to 62. received cannabis or sham treatment.
The researchers found no difference in reducing self-reported pain between using marijuana or placebo in the clinical trials: both showed a large improvement in pain. There was also no difference between the duration of treatment – 45 days or several months – both showed improvement in pain.
In clinical trials where blinding was most successful – people had no idea what treatment they were receiving – the placebo response was greater. Participants reported that their pain was moderately to significantly less severe after treatment with a placebo compared to before treatment.
A unique part of the study looked at the role of news and social media for the placebo effect in cannabis clinical trials, Jensen said. The researchers found positive media coverage after each of the cannabis clinical trials, even when the study results were less than spectacular, she said.
“Extensive positive media attention may shape placebo responses in subsequent clinical trials, but the current study is underpowered to address this possibility,” the study said.
More research is needed to understand whether this formation of placebo responses actually happens, Jensen said.
“It’s really hard to say where people get their information about what they expect the drug to do,” de Wit said. “I don’t think you can explain the placebo effect or blame it on social media. But you could tell that’s where they got the expectation that this drug would ease their pain – there’s a lot of social media saying that weed is good for everything under the sun.”
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