A US review of 25 studies assessing the safety and efficacy of cannabinoids in treating chronic pain has uncovered mixed results, but medics have blamed the ‘war on drugs’ for limiting the evidential base for the medicine.

Researchers from Oregon Health & Science University reviewed 18 randomised, placebo-controlled trials (1,740 participants), and seven cohort studies (13,095 participants), to evaluate the benefits and harms of cannabinoids for chronic pain.

Patients were asked to assess their pain before, during and after treatment.

The authors found that synthetic products with high THC-to-CBD ratios were associated with moderate improvement in pain severity and response, but an increased risk for sedation and dizziness. 

However, they said evidence for whole-plant products, CBD, and other cannabinoids was limited by imprecision, a lack of ability to assess consistency and poor methodology. 

They also noted that the reviewed studies did not evaluate harm outcomes including psychosis, cannabis use disorder, and cognitive deficits, or include patients who were at higher risk for harms.

Lead author Professor Marian McDonagh said the review found a surprising lack of evidence for using cannabis to treat pain.

She said: “In general, the limited amount of evidence surprised all of us. With so much buzz around cannabis-related products, and the easy availability of recreational and medical marijuana in many states, consumers and patients might assume there would be more evidence about the benefits and side effects. 

“War on drugs policies… have overwhelmingly favoured studying cannabis-related harms over therapeutic effects.”

PROFESSOR KEVIN BOEHNKE AND DR DANIEL CLAUW, UNIVERSITY OF MICHIGAN

“Unfortunately, there is very little scientifically valid research into most of these products.

“We saw only a small group of observational cohort studies on cannabis products that would be easily available in states that allow it, and these were not designed to answer the important questions on treating chronic pain.” 

The federally funded review, published in the Annals of Internal Medicine, will be updated on an ongoing basis.

However, commenting in the same journal, University of Michigan anaesthiologists blamed the ‘war on drugs’ for the limitations uncovered by the study.

Professor Kevin Boehnke and Dr Daniel Clauw wrote: “These limitations are well documented in the cannabinoid and chronic pain literature and are due in part to ‘war on drugs’ policies that have overwhelmingly favoured studying cannabis-related harms over therapeutic effects. 

“Unfortunately, this means that this well-conducted review found limited generalisable evidence to inform long-term use of available cannabis products for chronic pain.”

Prior to launching Cannabiz, Martin was co-founder and CEO of Asia-Pac’s leading B2B media and marketing information brand Mumbrella, overseeing its sale to Diversified Communications in 2017. A journalist...