When David Hao, an algologist at Massachusetts General Hospital in Boston, talks to a new patient suffering from chronic pain, the conversation usually goes like this: He lists his patient possible treatments, including injections of steroidal anti-inflammatory drugs, ablation of pain nerves , acupuncture sessions, physiotherapy or surgery. But at the end of the date, some people don’t hesitate to ask her, “Do you think I should try marijuana?” »
Patients have heard (perhaps through family, friends or the media) that cannabis and compounds derived from it, cannabinoids, can ease the pain they suffer from. As a scientist, however, Hao gives them an honest answer: “Based on the available data, the benefits are questionable. To date, authoritative studies have failed to conclude that cannabinoids reduce pain sufficiently, leading the International Association for the Study of Pain to do not approve these drugs.
The lack of evidence was underline last year in a systematic review published in JAMA network open. The researchers found that pain relief was 67% greater in individuals treated with cannabinoids than in those who received the placebo. This suggests that the pain relief was not primarily due to the compounds in the cannabis, but to the participants’ expectation that it would relieve pain. This positive expectation was in part the result, according to the authors, of overenthusiastic media coverage.
Medical cannabis is available in all forms of medicine, including products to be smoked or swallowed, with low or high doses of tetrahydrocannabinol (THC), the molecule responsible for the psychotropic effects associated with the use of marijuana, or cannabidiol (CBD), a compound that does not have hallucinatory effects. According to the study published in JAMA, the popular press (including major newspapers) regularly praise the plant’s benefits for pain relief.
Also according to this study, positive articles were published in the media while the conclusions of the scientific studies cited were neutral or negative, explains Karin Jensen, a researcher at the Pain Neuroimaging Lab of the Karolinska Institute in Sweden, who conducted the study. . National Geographic could not independently verify this claim due to a confidentiality agreement signed between the researchers and the London-based Altmetric database, which prohibits them from sharing the articles Jensen’s team evaluated for the study. JAMA.
“It seems that the media refuses to face the truth […] because whatever the conclusions of the trials, they will report them in a positive light. No wonder people keep asking for this kind of treatment,” says Jensen.
According to the US Centers for Disease Control and Prevention (CDC), one in five Americans currently living with chronic pain. This is why it is crucial in the context of patient care that the results of future studies on the pain effects of cannabinoids are not presented as positive to meet a trend, Hao points out.
BLIND TEST DIFFICULT TO IMPLEMENT IN THE CASE OF CANNABIS
In any type of clinical trial, when a patient does not receive a therapeutic compound but a neutral substitute such as a sugar pill and reports positive effects, this is called the placebo effect. The gold standard in clinical trials is the double-blind protocol where neither the participants nor the scientists know who is taking the active drug and who is taking the placebo.
Most studies that have tested cannabis-derived compounds have used tablets (sometimes inhalations) to deliver precise amounts of the drug. Additionally, the researchers made sure that the placebo smelled and tasted the same as the active drug. But sometimes participants guess which of the two tablets they took based on their next condition. When participants know they have received the real drug, their perception of the drug’s effectiveness can be skewed and skew study results.
Researchers at the Karolinska Institute wanted to understand the magnitude of the placebo effect in cannabis studies and therefore evaluated twenty reports involving 1,459 participants. One of the studios have analyzed, for example, compared a synthetic cannabinoid, nabilone, and a placebo with patients suffering from fibromyalgia. The co-authors of the paper concluded that the drug had a significant benefit, in part because the blinded trials, as is the case with many studies, overestimated the drug’s effects.
To counteract participants’ ability to guess what they were prescribed, researchers sometimes gave them small doses of the drug or gave them THC-free concoctions so they didn’t have mind-altering effects and couldn’t take it. took the drug.
However, with a substance so many people are used to, blinded cannabis studies require enormous precautions, says Deepak D’Souza, a professor of psychiatry at the Yale School of Medicine Clinic, who has been studying cannabis for more than two decades and is preparing a large-scale clinical trial on cannabinoids at the US Department of Veterans Affairs.
“Most of the studies did not apply the blinding system correctly. And even these methods are not perfect,” she explains. One is to give very small doses to some participants and larger doses to others, so that at least some individuals do not experience mind-altering effects. It is also possible to add a decongestant to a placebo so that people taking it also show some physiological symptoms. Third way: Give all participants a placebo so they have a harder time guessing what they took.
D’Souza says it’s also important to determine patients’ expectations of the benefits of marijuana-derived products. “You can do this by asking simple questions” and then analyzing them taking into account that people with positive expectations about cannabis are likely to show more positive outcomes, she explains.
THE BRAIN HAS A CENTRAL ROLE IN PAIN MANAGEMENT
Unlike some chronic diseases, painful conditions can be particularly sensitive to the placebo effect. This is the case for the types of pain known as nociplastic pain. This pain, unlike that caused by tissue or nerve damage (nociceptive pain and neuropathic pain, respectively), results from alterations in the sensory system. Common diseases that cause nociplastic pain include fibromyalgia, irritable bowel syndrome, and tension headaches, among others. This pain is as real and harmful as any other, but it has the potential to do so do not fade away under the influence of medicines or treatments usually prescribed.
(Read: Scientists unlock the mysteries of pain)
Experts don’t yet understand the precise mechanisms at work in nociplastic pain, but they speculate that thinking may have a role to play in the process. For example, we observe on MRI images that brain regions involved in pain perception and modulation switch on when the patient thinks, especially when he has negative thoughts about his pathology.
Hao believes people with this pain may be particularly prone to the placebo effect. “I think it is not absurd to think that in this group of patients the role of expectations is potentially exaggerated”, she explains, recalling however that the issue remains to be investigated.
(Read: Chronic pain perception is largely psychological in origin)
One is tempted to say that it doesn’t matter whether the positive results seen in clinical cannabis trials are a result of taking medication or the placebo effect, as long as the pain is reduced. But it’s not that simple, says Jensen. “It’s not enough to know that something works. We must know because works to best help patients. explains. “If we prescribe effective treatments for reasons other than the mechanism in place, we won’t be able to help people in the long run,” who may be better off with other therapies.
“Patients may be satisfied in the short term when their doctor recommends cannabis,” notes Jensen, “but at this time the scientific evidence does not support the compound’s efficacy in treating pain. »