Medical cannabis greatly interests researchers studying symptoms of certain neurological disorders, including epilepsy, Parkinson's disease, and multiple sclerosis (MS).
To date, only a handful of studies have focused on the effects of cannabinoids on symptoms of neurological disorders other than MS. While limited, research has found associations between medical cannabis and the potential improvement of specific symptoms across all three disorders listed above, including a reduction in pain and epileptic seizures.
“It's difficult to generalize cannabis' effects across these three disorders because they are quite different and in some ways opposing,” said Dr. Adie Wilson-Poe, Ph.D., a neuroscientist and instructor at Washington University in St. Louis and a scientific adviser to Weedmaps.
Impact of Cannabinoids on the Central Nervous System
In the late 1980s and early '90s, researchers identified and cloned two cannabinoid receptors, CB1 and CB2. This supported a major effort to understand the physiological roles and mechanisms associated with the endocannabinoid system (ECS).
The CB1 receptor is found in particularly high levels in the cerebellum, neocortex, basal ganglia, and brain stem. This receptor has been explored as a potential therapeutic agent for neurodegenerative and neuropsychological disorders.
Given the widespread distribution of CB1 receptors in the human body, researchers believe that an extensive spectrum of possible physiological roles exists, showcasing the complexity of the ECS. For example, researchers at the University of British Columbia found that CB1 receptors have been shown to inhibit glutamate and gamma-aminobutyric acid (GABA) release from presynaptic terminals — a possible and plausible mechanism of CB1 receptor-mediated neuroprotection. Presynaptic terminals are the location in our cells where neurotransmitters function.
While CB1 receptors affect motor and cognitive function, CB2 receptors may play a more critical role in neuroprotection and neuroinflammation.
Cannabis and Epilepsy
Affecting about 2 million Americans, epilepsy is a neurological disorder that impacts people of all ages. Anticonvulsant drugs have been shown to completely suppress seizures in around 60 percent of patients. However, these medications also often cause side effects, including increased drowsiness, headaches, tremors, and possible hair loss.
Researchers are currently interested in the potential relationship between seizure-suppressing cannabinoids and the vast number of CB1 receptors in the amygdala and hippocampus. These regions are where partial seizures originate, providing a possible treatment option for the 30 percent of patients who experience drug-resistant epilepsy.
“Mechanistically, we know that cannabis may reduce seizures in epilepsy by reducing neurotransmitter release, as well as reducing the brain's sensitivity to stimulating (excitatory) neurotransmitters like glutamate,” Wilson-Poe said.
Review evidence has shown that a CBD dose of 20 mg per kg of patient weight per day was more effective than a placebo, reducing seizure frequency by 50 percent or greater. Based on 14 observational studies, 8.5 percent of pooled participants experienced seizure freedom, with higher estimates reported among pediatric samples.
While more research is needed, a 2018 analysis in Epilepsia, the journal of the International League Against Epilepsy, indicated that the use of cannabinoids for the treatment of pediatric epilepsy looks promising. Evidence from high-quality, short-duration randomized control studies suggests that cannabidiol (CBD) may be effective in reducing the number of seizures children have by 50 percent or more.
Any reduction in seizure frequency can have an immense impact on the lives of these children, which is why a dramatic increase in the number of studies conducted over the next few years is expected to sharply increase.
Cannabis and MS
In the United States, there are about 400,000 people living with MS — with around 200 new cases diagnosed each week. Recent studies have shown that there is wide acceptance of cannabis among the MS community, with between 20 to 60 percent of patients currently using cannabis for medicinal purposes, according to a 2017 report in Frontiers in Neurology.
Unlike epilepsy, MS is a demyelinating, or destructive of nerve tissue, disease of the central nervous system, resulting in a range of debilitating symptoms that impact one's quality of life. Wilson-Poe provided insight into the two major components of MS — spasticity, or muscle spasms, as well as pain.
“The mechanisms behind cannabis' effects on pain are pretty clear; involving a change in neurotransmission in the brain's pain headquarters, which is located in the midbrain,” she said. “However, the mechanisms behind improved spasticity are not clear. The improved muscle control/motor control in Parkinson's might be the same or a similar phenomenon that's happening with MS patients, but more research is needed.”
Cannabis and Parkinson's Disease
In comparison to epilepsy and MS, less is known about the relationship between Parkinson's disease and cannabis.
“Although there have been clinical trials looking at cannabis' effects in MS patients, these clinical trials have not been conducted for Parkinson's patients,” Wilson-Poe said. “The evidence for cannabis' effectiveness for Parkinson's is definitely not as strong.”
While the available research is sparse and largely observational, Parkinson's disease remains one of the qualifying conditions for medical cannabis eligibility across many states. Medical cannabis is of particular interest as a way to potentially decrease the use of more potent prescription drugs, including opioids for pain.
One 2017 study published in Clinical Neuropharmacology focused on the potential effects of medical cannabis on symptoms of Parkinson's disease. Improvements were observed in regards to the number of falls, pain levels, mood, tremors, sleep, and muscle stiffness.
While cannabis science and research are still in their infancy, researchers around the world continue to explore and unlock its potential. Many questions remain with regard to variables such as metabolism in the body, potency, dosage, and any possible adverse effects.