Cannabis is one of the most widely used drugs (opens in new tab) in the world. While there are few countries where cannabis is legal for recreational use, many more countries have legalized the use of cannabis for medicinal purposes (opens in new tab).
reduce pain (opens in new tab) is one of the most common reasons people report using medicinal cannabis. According to a US national survey, 17% of respondents (opens in new tab) who reported having used cannabis in the past year were prescribed medical cannabis. When it comes to self-medication, the numbers are even higher – with estimates ranging from 17-30% (opens in new tab) of adults in North America, Europe and Australia report using it to treat pain.
While cannabis (and cannabis-derived products like CBD) can be widely used to relieve pain, it’s still unclear how effective it really is. This is what our recent systematic review and meta-analysis aimed to uncover. Our study, published in the Journal of the American Medical Association, suggests that cannabis is no better at relieving pain (opens in new tab) as a placebo.
To conduct our study, we looked at the results of randomized controlled trials comparing cannabis to placebo for the treatment of clinical pain. We specifically included studies that compared the change in pain intensity before and after treatment. In total, we looked at 20 studies involving almost 1,500 people.
The studies we included looked at a variety of different pain conditions (e.g. neuropathic pain caused by nerve damage and multiple sclerosis) and types of cannabis products – including THC, CBD and synthetic cannabis (like nabilone). These treatments have been administered in a variety of ways, including via pills, sprays, oil, and incense.
The majority of study participants were female (62%) and between 33 and 62 years old. Most studies were conducted in the US, UK or Canada – although we also include studies from Brazil, Belgium, Germany, France, the Netherlands, Israel, the Czech Republic and Spain.
Our meta-analysis showed that pain was rated as significantly less intense after treatment with a placebo, with a moderate to large effect depending on the individual. Our team also observed no significant difference between cannabis and a placebo for pain relief.
This confirms the results of a meta-analysis from 2021 (opens in new tab). In fact, this 2021 meta-analysis also found that higher quality studies with better blinding procedures (where both participants and researchers do not know who is receiving the drug) actually had higher placebo responses. This suggests that some placebo-controlled cannabis studies do not ensure proper blinding, which may have led to an overestimation of the effectiveness of medicinal cannabis.
Our study also found that many participants could distinguish between a placebo and active cannabis despite the same smell, taste, and appearance. If they know they are receiving or not receiving cannabinoids, they are more likely to make a biased assessment of the effectiveness of the intervention. To ensure that researchers are observing the actual effects of cannabis, participants cannot know what they are receiving.
Our study also looked at the way the studies were covered by the media and scientific journals to see if this was related to the therapeutic effects reported by the participants. We did this because research has shown that media coverage and information on the internet can influence expectations (opens in new tab) that a person has treatment.
Media exposure was measured using the alt metric, a method of evaluating mentions of a study in media, blogs, and social media. Academic influence was measured using citations from other researchers. We found a total of 136 messages in the media and blogs.
We categorized the coverage as positive, negative, or neutral based on how the results were presented in relation to the effectiveness of cannabis for treating pain. The overwhelming majority of the news reported that cannabis had a beneficial effect in treating pain. This means that media coverage of cannabis tends to be positive, regardless of what the results of a study actually were.
There are numerous examples of the relationship between treatment expectations and placebo responses (opens in new tab). When a person believes that they will experience relief from their pain by using a particular product or treatment, it can change the way they ultimately perceive it (opens in new tab) incoming pain signals – leading them to believe that their pain is less severe. Recent evidence suggests that the placebo effect can work even when we are presented with evidence that contradicts our initial expectations (opens in new tab).
We cannot say with 100% certainty that media coverage is responsible for the high placebo response observed in our review. However, since placebos have been shown to be just as good as cannabis for pain management, our results show 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 like cannabinoids that get a lot of media attention, we need to be extra rigorous in our clinical trials.
This article is republished by The conversation (opens in new tab) under a Creative Commons license. read this original article (opens in new tab).