Medical Cannabis: Is it Really Just a Placebo?

If you read a media report on a study claiming to say something, it’s a reasonable bet that the study actually doesn’t say it. Case in point: A study ‘purporting’ to show that cannabis as a pain reliever is all just placebo. Of course the mainstream media was quick to pounce (if you do a google search you’ll find a lot of reports saying the same thing, including by some who should know better).

Cannabis is no better than a placebo for treating pain. That’s the claim of a new study of studies out of Sweden. Dr Filip Gedin is with the Pain Neuroimaging Lab at the Karolinska Institute, a research-led medical university in Stockholm and one of the world’s top medical schools.

The study also examined the way media coverage may affect a patient’s expectations of cannabis in treating pain.

One of the first things to do is ask where did the study come from? For example, countries that are pro-prohibition are more likely to approve grants to studies purporting to show that cannabis is ‘bad for you’. The study is from Sweden, a country notoriously pro-prohibition (a nation, by the way, that has the fourth highest overdose rate in the world).  That should send alarm bells.

Next, ask who actually funded the study. In this case it’s hard to tell (many studies will actually tell you explicitly who funded it).

Overall though, even given the source of the study, there’s no real evidence that the study itself is biased. So far, so good.

Let’s now dive into the study itself.

First, the study is a meta-study of 20 other studies. That in itself is fine. But as the paper admits:

This study has limitations. Because this meta-analysis combines trials with different settings, levels of quality and lengths of follow-up, heterogeneity is to be expected.³⁷ The data extracted for the meta-analysis had some considerable heterogeneity; therefore, the results need to be interpreted with caution. To address heterogeneity, we used a random-effects model, recommended by Borenstein et al.³⁸ Post hoc analyses were not applied to the meta-analytical data. However, before the start of the study, our hypotheses and analyses were preregistered. We used a small number of moderators and did not implement post hoc analyses because we limited our search to a handful of predefined and independent comparisons.

Next, let’s have a look at what the study  says:

The data from the present meta-analysis, including 1459 patients with clinical pain, suggest that placebo responses contribute significantly to the pain reduction seen in cannabinoid randomized clinical trials. The size of the improvements in the placebo group was moderate to high and represents clinically relevant pain relief.

Notice how the study only uses the word “suggest” and says that with regards to the placebo group the improvements were (statistically) significant. That’s a far cry from the media claiming “Cannabis is no better than a placebo for treating pain.”

But anyway, at the end of the day, what does the study actually conclude?

The findings of this systematic review and meta-analysis suggest that placebo responses contribute significantly to pain reduction in cannabinoid clinical trials. 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.

So basically if you’ve read a lot of media saying cannabis can cure pain, and you really want to believe it does, you’re far more likely to think it’s fixing your pain, even if it’s mostly in your head.

Talk about stating the bleedin’ obvious.