By Pat Anson, PNN Editor

Medical marijuana advocates are challenging the findings of a new study that found little clinical evidence to support the use of cannabis in treating chronic pain.

“The findings appear out of step with the real-world experience of millions of patients who have come to rely on cannabis for pain management,” said Paul Armentano, Deputy Director of NORML.

The federally-funded systematic review – essentially a study of studies – was conducted by researchers at Oregon Health & Science University (OHSU), who analyzed over 3,000 cannabis studies. They could find only 25 studies that met their criteria for review. Only placebo controlled clinical trials or observational studies lasting at least four weeks were included. The rest were deemed to be poor quality or flawed in some way.

“In general, the limited amount of evidence surprised all of us,” said lead author Marian McDonagh, PharmD, professor of medical informatics and clinical epidemiology in the OHSU School of Medicine. “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.”

‘Biased Findings’

Most of the 25 cannabis studies that met OHSU’s criteria for review were considered biased in some way — 30% of the clinical trials were considered to have “high risk of bias” and half had “medium risk of bias.”  Most of the observational studies were also considered biased.

Despite the limited evidence, the OHSU research team came to some sweeping conclusions. Their study, published in the Annals of Internal Medicine, found no evidence to support the use of cannabidiol (CBD) or cannabis leaves, buds and flowers in treating pain. Only synthetic cannabis products rich in tetrahydrocannabinol (THC) were found to provide short-term relief from neuropathic pain.

Curiously, the OHSU researchers included in their review studies that evaluated the effectiveness of dronabinol and nabilone, two cannabis-based medications that are only FDA-approved to treat nausea, vomiting and weight loss. They are not formulated to treat chronic pain. Similarly, another study looked at the effectiveness of a cannabis extract in treating muscle stiffness (spasticity) caused by multiple sclerosis.

“It would appear that authors' relatively narrow focus and emphasis on both synthetic cannabis formulations (which historically have not demonstrated similar efficacy to whole-plant cannabis) as well as upon extracts that were initially designed to target medical ailments other than pain management may have biased these findings,” Armentano said in an email to PNN. 

“Numerous controlled trials involving whole-plant cannabis and reviews of said trials have determined that there exists substantial evidence that cannabis is safe and effective in pain management, particularly for neuropathy.” 

Armentano said nearly two-thirds of people enrolled in state-run medical cannabis programs registered for the treatment of chronic pain.

“Controlled studies have further indicated that cannabinoids can act synergistically with opioids, resulting in patients requiring lower doses to achieve relief. This is likely why we now have dozens of studies finding that pain patients taking opioids who initiate medical cannabis use frequently reduce or eliminate their opioid use over time,” Armentanohe said.

More Studies Needed

The OHSU researchers say more high-quality studies are needed on the safety and efficacy of cannabis products, which are largely unregulated by the FDA.

“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,” co-author Roger Chou, MD, director of OHSU’s Pacific Northwest Evidence-based Practice Center said in a press release. “That makes it tough for patients and clinicians, since the evidence for one cannabis-based product may not be the same for another.”

Chou is a controversial figure in the pain community. A prolific researcher and frequent critic of opioid prescribing, Chou co-authored the CDC’s controversial 2016 opioid guideline. Although he has acknowledged conflicts of interest, Chou remains as one of the co-authors of a revised CDC guideline, which is expected to be released later this year.

The cannabis findings are similar to those in another OHSU review, which found no clinical evidence to support the use of kratom, an herbal supplement used by millions of Americans to relieve pain, anxiety, depression and other medical conditions.     

The studies on cannabis, kratom and other plant-based treatments are potentially worth up to $1.4 million for OHSU, a public research university that the federal government often turns to for medical research. According to the website GovTribe, in the last five years OHSU has been awarded nearly $2 billion in federal research grants, much of it coming from the Agency for Healthcare Research and Quality (AHRQ).