PHILADELPHIA – Medical marijuana research to date provides some support for its use in neuropathic pain, nausea and vomiting, and spasticity, some insights into adverse effects, and “a lot of the Wild West,” Ellie Grossman, MD, MPH, said here at the annual meeting of the American College of Physicians.

The opioid-sparing effects of medical marijuana have been highlighted in recent reports suggesting that cannabis users may use less opioids, and that states with medical marijuana laws have seen drops in opioid overdose mortality, Dr. Grossman said.

“That’s kind of a story on pain and cannabinoids, and that’s really the biggest story there is in terms of medical evidence and effectiveness for this agent,” said Dr. Grossman, an instructor at Harvard Medical School and Primary Care Lead for Behavioral Health Integration, Cambridge Health Alliance, Somerville, Mass.

However, being the top story in medical marijuana may not be a very high bar in 2019, given current issues with research in this area, including inconsistencies in medical marijuana formulations, relatively small numbers of patients enrolled in studies, and meta-analyses that have produced equivocal results.

“Unfortunately, this is an area where there’s a lot of, shall I say, ‘squishiness’ in the data, through no fault of the researchers involved – it’s just an area that’s really hard to study,” Dr. Goodman said in her update on medical marijuana use at the meeting.

Most studies of cannabinoids for chronic pain have compared these agents to placebo, rather than the long list of other medications that might be used to treat pain, Dr. Grossman said.

There are several meta-analyses available, including a recently published Cochrane review in which authors concluded that, for neuropathic pain, the potential benefits of cannabis-based medicines may outweigh their potential harms.

“The upshot here is that there may be some evidence for neuropathic pain, but the evidence is generally of poor quality and kind of mixed,” said Dr. Grossman.

State-level medical cannabis laws were linked to significantly lower opioid overdose mortality rates in a 2014 study (JAMA Intern Med. 2014;174[10]:1668-73). In more recent studies, states with medical cannabis laws were found to have lower Medicare Part D opioid-prescribing rates, and in another study, legalization of medical marijuana was linked to lower rates of chronic and high-risk opioid use.

“It certainly seems like maybe we as prescribers are prescribing [fewer] opioids if there’s medical cannabis around,” Dr. Grossman said. “What this means for our patients in the short term and long term, we don’t totally know. But clearly, fewer opioid overdoses is a way better thing than more, so there could be something here.”

The cannabinoids approved by the Food and Drug Administration include nabilone (Cesamet) and dronabinol (Marinol), both synthetic cannabinoids indicated for cancer chemotherapy–related nausea and vomiting, along with cannabidiol (Epidiolex), just approved in June 2018 for treatment of some rare pediatric refractory epilepsy syndromes, Dr. Grossman said.

For chemotherapy-induced nausea and vomiting, evidence suggests oral cannabinoids are more effective than placebo, but there’s mixed evidence as to whether they are better than other antiemetics, Dr. Grossman said, while in terms of spasticity related to multiple sclerosis, research has shown small improvements in patient-reported symptoms.

Long-term adverse event data specific to medical marijuana are scant, with much of the evidence coming from studies of recreational marijuana users, Dr. Grossman said.

Those long-term effects include increased risk of pulmonary effects such as cough, wheeze, and phlegm that improve with discontinuation; case reports of unintentional pediatric ingestions; and lower neonatal birth weight, which should be discussed with women of reproductive age who are using or considering medical marijuana, Dr. Grossman said.

Motor vehicle accidents, development of psychiatric symptoms, and psychosis relapse also have been linked to use, she said.

Some real-world adverse event data specific to medical marijuana data are available through the Minnesota medical cannabis program. They found 16% of surveyed users reported an adverse event within the first 4 months, including dry mouth, fatigue, mental clouding, and drowsiness, Dr. Grossman told attendees.

Dr. Grossman reported that she has no relationship with entities producing, marketing, reselling, or distributing health care goods or services consumed by, or used on, patients.

SOURCE: Grossman E. ACP 2019, Presentation MTP 010.

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