Another marijuana-based drug, nabiximols (Sativex), is available in Canada and several European countries to treat spasticity and nerve pain in patients with multiple sclerosis.
Medicinal cannabis is hardly a new therapeutic agent. It was widely used as a patent medicine in the United States during the 19th and early 20th centuries and was listed in the United States Pharmacopoeia until passage of the Marijuana Tax Act in 1937 rendered it illegal.
Then a federal law in 1970 made it a Schedule 1 controlled substance, which greatly restricted access to marijuana for legitimate research. Also complicating attempts to establish medical usefulness is that plants like marijuana contain hundreds of active chemicals, the amounts of which can vary greatly from batch to batch. Unless researchers can study purified substances in known quantities, conclusions about benefits and risks are highly unreliable.
That said, as recounted in Dr. Finn’s book, here are some conclusions reached by experts about the role of medical marijuana in their respective fields:
People using marijuana for pain relief do not reduce their dependence on opioids. In fact, Dr. Finn said, “patients on narcotics who also use marijuana for pain still report their pain level to be 10 on a scale of 1 to 10.” Authors of the chapter on pain, Dr. Peter R. Wilson, pain specialist at the Mayo Clinic in Rochester, Minn., and Dr. Sanjog Pangarkar of the Greater Los Angeles V.A. Healthcare Service, concluded, “Cannabis itself does not produce analgesia and paradoxically might interfere with opioid analgesia.” A 2019 study of 450 adults in the Journal of Addiction Medicine found that medical marijuana not only failed to relieve patients’ pain, it increased their risk of anxiety, depression and substance abuse.
Dr. Allen C. Bowling, neurologist at the NeuroHealth Institute in Englewood, Colo., noted that while marijuana has been extensively studied as a treatment for multiple sclerosis, the results of randomized clinical trials have been inconsistent. The trials overall showed some but limited effectiveness, and in one of the largest and longest trials, the placebo performed better in treating spasticity, pain and bladder dysfunction, Dr. Bowling wrote. Most trials used pharmaceutical-grade cannabis that is not available in dispensaries.
The study suggesting marijuana could reduce the risk of glaucoma dates back to 1970. Indeed, THC does lower damaging pressure inside the eye, but as Drs. Finny T. John and Jean R. Hausheer, ophthalmologists at the University of Oklahoma Health Sciences Center, wrote, “to achieve therapeutic levels of marijuana in the bloodstream to treat glaucoma, an individual would need to smoke approximately six to eight times a day,” at which point the person “would likely be physically and mentally unable to perform tasks requiring attention and focus,” like working and driving. The major eye care medical societies have put thumbs down on marijuana to treat glaucoma.
Allison Karst, a psychiatric pharmacy specialist at the V.A. Tennessee Valley Healthcare System, who reviewed the benefits and risks of medical marijuana, concluded that marijuana can have “a negative effect on mental health and neurological function,” including worsening symptoms of PTSD and bipolar disorder.
Dr. Karst also cited one study showing that only 17 percent of edible cannabis products were accurately labeled. In an email she wrote that the lack of regulation “leads to difficulty extrapolating available evidence to various products on the consumer market given the differences in chemical composition and purity.” She cautioned the public to weigh “both potential benefits and risks,” to which I would add caveat emptor — buyer beware.