Cannabis product use provides modest, short-term improvements in chronic pain, albeit with some side effects, according to a large review of research on cannabis pain management. The review also revealed a general lack of high quality evidence such as randomised controlled trials (RCTs). The data will be uploaded to a web app made by Oregon Health & Science University to inform clinicians on cannabis medications.
Reporting in Annals of Internal Medicine, researchers found evidence to support a short-term benefit in treating neuropathic pain with two synthetic products with 100% tetrahydrocannabinol (THC): dronabinol (under the trade name Marinol) and nabilone (Cesamet). Another product, a sublingual spray of equal parts THC and cannabidiol (CBD), known as nabiximols, also showed evidence of some clinical benefit for neuropathic pain. All of the products had side effects, such as nausea, sedation and dizziness.
From 3000 studies, the researchers selected RCTs or comparative observational studies of patients with chronic pain that compared cannabis products with a placebo or no treatment (that is, usual care) for at least 4 weeks of treatment or follow-up.
They ended up with a total of 25 with scientifically valid evidence – 18 RCTs and seven observational studies. Cannabinoids were categorised as high, comparable, or low THC-to-CBD ratio. The researchers found:
- Synthetic products with high THC (> 98%) and little or no CBD: moderate improvement in pain, but greater sedation risk and possible increase in dizziness
- Extracted products with majority THC (THC:CBD ratio ranging from 3:1 to 47:1): no significant improvement in pain, but greater study withdrawal because of adverse events and dizziness
- Sublingual sprays with comparable THC and CBD levels: small improvement in pain but a much greater increased risk of dizziness and sedation and a moderate increase in nausea
Besides these findings, there was little evidence to support any other conclusions.
“In general, the limited amount of evidence surprised all of us,” said lead author Marian S. McDonagh, PharmD, emeritus professor at OHSU. “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.
“Unfortunately, there is very little scientifically valid research into most 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.”
“For some cannabis products, such as whole-plant products, the data are sparse with imprecise estimates of effect and studies had methodological limitations,” the authors noted.
This situation makes it difficult to guide patients.
“Cannabis products vary quite a bit in terms of their chemical composition, and this could have important effects in terms of benefits and harm to patients,” said co-author Roger Chou, MD. “That makes it tough for patients and clinicians since the evidence for one cannabis-based product may not be the same for another.”
The living review, including a visual abstract summary of the findings, will also be shared on a new web-based tool launched by OHSU and VA Portland Health Care System early this year to help clinicians and researchers evaluate the latest evidence around the health effects of cannabis. Known as Systematically Testing the Evidence on Marijuana, or STEM, the project includes ‘clinician briefs’ to help health care workers translate the clinical implications.
“This new living evidence review is exactly the type of resource clinicians need to clarify for patients the areas of potential promise, the cannabis formulations that have been studied and, importantly, the major gaps in knowledge,” said co-author Devan Kansagara, MD, MCR, professor of medicine at OHSU.
