Experts may be moving toward accepting cannabis as a useful tool to treat neuropathic pain, a recent debate on the topic suggests. During the debate, one expert argued for, and another against, there being sufficient evidence for the use of cannabis to treat neuropathic pain, but in the end, they agreed that some patients do benefit.
The discussion took place at the Congress of the European Academy of Neurology (EAN) 2020, which transitioned to a virtual online meeting because of the COVID-19 pandemic.
The cannabis plant has 460 constituents. The two main components are tetrahydrocannabinol (THC) and cannabidiol (CBD). It can be consumed by swallowing oil extracts, by the sublingual route, or by smoking or eating the plant. Cannabis medications already in use include oral THC (nabilone, dronabinol) and an oral mucosal spray, nabiximols (Sativex).
Arguing that therapeutic cannabis is helpful for neuropathic pain, Elon Eisenberg, MD, professor of neurology and pain medicine, Israel Institute of Technology, Haifa, cited a number of encouraging randomized, controlled trials and meta-analyses of studies on the subject.
Dr. Eisenberg discussed three relevant articles. One was a 2016 viewpoint article published in JAMA that concluded that “cannabis seems to be a substitute, a rather good one, for opioids,” said Dr. Eisenberg.
A “comprehensive” 440-page review, published by the National Academies Press in 2017, evaluated the evidence to that point and “came to the conclusion there is substantial evidence that cannabis is an effective treatment for chronic pain in adults,” said Dr. Eisenberg.
And a 2018 position paper from the European Pain Federation determined that “the quantity and quality of evidence is such that cannabis-based medicines may be reasonably considered for chronic neuropathic pain,” he said.
He noted that the most recent results from an Israeli prospective cohort registry study that is following more than 851 patients who are taking cannabis over 1 year are positive. Analyses show a steady reduction in pain intensity and improvements in catastrophizing and disability. Importantly, he said, participants are using fewer opioids. However, about 40% of patients in that registry study experienced some adverse event, although most were not serious, said Dr. Eisenberg.
Arguing on the other side – that therapeutic cannabis is not helpful for neuropathic pain – was Nadine Attal, MD, PhD, professor of therapeutics and pain at the University Versailles Saint Quentin, France. She questioned the quality of some of the research to date and stressed that studies should consider neuropathic pain as a primary outcome – not spasticity or pain in general. They should also be double-blind, randomized, and placebo controlled, she said.
In addition, she said these studies should enroll at least 10 patients per group and should continue for 3 weeks or longer.
Dr. Attal wondered which of the many plant derivatives (phytocannabinoids) are used in cannabis studies.
She discussed four meta-analyses or reviews on the topic, some of which she said are “heterogeneous” and don’t provide convincing evidence for cannabis use in neuropathic pain.
For example, one review examined only marijuana, and all studies in it were short term. One of the studies in this review was of spasticity. Another review included two studies of cancer pain, and the most positive study in NP used short-term inhaled THC.
“There is no evidence to date that cannabinoids, including nabiximols or oral THC, administered for at least 3 weeks are more effective than placebo in neuropathic pain,” she concluded.