Only 7 randomized trials have tested smoked cannabis, and the evidence for most conditions was limited | Research

The takeaway

A review found only 7 randomized placebo-controlled trials of smoked cannabis, with evidence supporting calorie intake increase but not pain relief, and a glaucoma benefit too brief to be useful.

Read this if you smoke cannabis for medical reasons and want to know what the placebo-controlled evidence actually shows.

Only 7 randomized trials of smoked cannabis despite 90% of users choosing this route

What the researchers found

Despite 90% of marijuana users in 2014 using the smoked form, researchers could find only seven randomized placebo-controlled trials that specifically tested smoked cannabis for medical purposes.

The results were mixed. Cannabis did not outperform placebo for experimentally evoked pain or for improving the timed walk test. For glaucoma, smoked cannabis did reduce intraocular pressure, but the effect lasted less than four hours, making it impractical for this chronic condition.

The most consistent finding was that smoked marijuana, even at lower THC concentrations, increased total daily calorie intake and number of eating occasions. This appetite-stimulating effect was robust across studies.

Neither of the studies examining quality of life as a secondary outcome found significant improvements with cannabis use.

Why it matters

The overwhelming majority of medical cannabis use involves smoking, yet the evidence base for this specific route of administration is remarkably thin. With only seven qualifying trials, policy decisions about medical marijuana are being made with very limited evidence for the way most patients actually use it.

The numbers in context

90% of marijuana users in 2014 used smoked form. Only 7 RCTs met inclusion criteria. 28 states had legalized medical marijuana at time of publication. Cannabis did not beat placebo for pain or walking tests. Glaucoma pressure reduction lasted less than 4 hours. Consistent increase in daily calorie intake.

How the study worked

A systematic literature search identified randomized controlled trials studying smoked cannabis for medical conditions. Only studies with smoked cannabis (excluding other administration methods), placebo controls, and disease-specific primary endpoints were included. Open-label studies were excluded. Seven studies met all criteria.

What this study cannot tell us

The small number of qualifying trials limits the ability to draw broad conclusions. The strict inclusion criteria excluded studies using other delivery methods that might inform the effects of cannabis. Some conditions may benefit from smoked cannabis in ways not captured by the specific outcomes measured. The review was published early in the modern era of cannabis research.

How to read the evidence

This is a systematic review of randomized controlled trials, but the very small number of qualifying studies limits the evidence strength.

When this study was published

Published in 2018. More RCTs of various cannabis delivery methods have been conducted since.

The bigger picture

This review highlights a fundamental evidence gap in cannabis medicine: the disconnect between how patients use cannabis (overwhelmingly smoked) and how it is studied (increasingly through oral formulations, vaporizers, or pharmaceutical preparations). This gap makes it difficult to translate clinical trial evidence to real-world patient experiences.

Questions still open

Should more clinical trials be designed around the smoked route of administration that most patients actually use? Is the appetite-stimulating effect of smoked cannabis clinically useful for wasting conditions? Would longer-duration studies produce different results for pain outcomes?

Common questions

Does smoked cannabis work for pain?

In the seven randomized placebo-controlled trials identified by this review, smoked cannabis did not outperform placebo for experimentally evoked pain. However, the small number of trials means this is not a definitive conclusion.

Why are there so few studies of smoked cannabis?

Regulatory barriers to cannabis research, ethical concerns about combustion-based delivery in clinical trials, and the difficulty of creating a convincing placebo for smoked cannabis all contribute to the limited research base.

Read the original research

Therapeutic Benefit of Smoked Cannabis in Randomized Placebo-Controlled Studies.

Pharmacotherapy, 38(1), 80-85

View on PubMed ↗Publisher’s paper ↗

Citation

Bowen, Lynneice L; McRae-Clark, Aimee L. (2018). Therapeutic Benefit of Smoked Cannabis in Randomized Placebo-Controlled Studies.. Pharmacotherapy, 38(1), 80-85. https://doi.org/10.1002/phar.2064