6 reasons to be circumspect about medical cannabis

Physicians say the drug seems to hold some promise, but much more evidence is needed

While medical cannabis is promoted for conditions ranging from nausea to cancer, the paucity of high-quality evidence demands caution, according to six doctors across the US.


The editors of the Annals of Internal Medicine issued a call for readers' perspectives on prescribing or recommending marijuana. Six of the 100 submitted manuscripts for brief commentaries appear in the 8 January issue.

Here's a summary of the doctors' views: 

  1. Lack of evidence and standardisation
    Dr Chester Good from UPMC Health Plan, Pittsburgh, Pennsylvania, and colleagues lament the lack of high-quality evidence and the lack of standardisation of medical marijuana products. “Medical marijuana seems to hold some promise for treating pain, but much more evidence is needed,” Dr Good said.
  2. Not a first-line treatment for chronic pain
    Dr Kevin Boehnke and Dr Daniel Clauw from University of Michigan Medical School, Ann Arbor, do not regard cannabinoids as first-line treatments for chronic pain but as adjuvant therapies to be used before opioids if other options fail. "Cannabis is neither panacea nor poison,” he said.
  3. Cardiovascular risks
    Dr Tina Kaufman and colleagues from Oregon Health and Science University, Portland, highlight the hazards to older patients. “Emerging evidence suggests that smoking marijuana may have risks to cardiovascular health, particularly in older patients and those with known cardiovascular disease,” Dr Kaufman said.
  4. Marijuana not shown to be safe in pregnancy and lactation
    Dr Eli Adashi from the Warren Alpert Medical School, Brown University, Providence, Rhode Island, makes clear in his commentary that medical cannabis should be regarded as harmful until proved safe in pregnancy.  "Additional research is urgently required in experimental models including non-human primates,” he said.
  5. Upswing in emergency visits owing to marijuana exposure
    Dr Kennon Heard and colleagues of the emergency department at the University of Colorado School of Medicine have witnessed a dramatic increase in emergency department visits for cannabinoid-related hyperemesis, which was virtually unrecognised before, but now accounts for more than 100 patients a year.
  6. More scientific evidence needed
    Dr Jan Carney from Larner College of Medicine at the University of Vermont, Burlington, advocates a strategy that, among other things, aims to eliminate differences between what the public believes about marijuana use and what physicians know. “There are huge gaps between what we know from research and what is commonly believed," she said.