The existing research is promising, but researchers are calling for more clinical trials in humans.
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The fact that humans even have an "endocannabinoid system" sounds like stoner fantasy. (If we hadn't been trying to figure out just what cannabis does to our bodies when it was discovered, it might have received a different name.) But while the research on cannabinoids began in the '90s as a way to help us understand why pot affects so many areas of our health, the endocannabinoid system is now understood to be one of the most important physiological systems in our body.
"It's involved in virtually every aspect of our physical and emotional health," says Jeremy Kossen, clinical research director at the cannabis-focused Zana Medical Group. "It mediates inflammatory response, learning, memory, hunger, and cognitive function."
Put simply, cannabinoids are compounds that are both produced by the body (endocannabinoids) and found outside the body (like in marijuana). Your body contains a variety of cannabinoid receptors that they interact with, and we first thought that they were mostly involved with parts of the brain related to mood, appetite, and pain.
We now know that endocannabinoids and their receptors are also present in organs, connective tissues, glands, immune cells, and many parts of the brain that you wouldn't immediately associate with a plant best-known for making Encino Man seem Oscar-worthy.
Since the endocannabinoid system is so intricately connected with many areas of our health, it makes sense that disruptions in it can be a factor in a variety of common disorders, including neurodegenerative diseases like Alzheimer's, Parkinson's, and multiple sclerosis. And it's why researchers have found that an increase in certain cannabinoids can treat and maybe even reduce the risk of these diseases.
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To be clear, smoking ganja every day is not linked with better mental health. But in lab settings, certain compounds that are found in cannabis (like THC and CBD) have been linked to treating and even helping prevent neurodegenerative diseases.
The most promising evidence points to cannabinoids reducing the formation of plaques in the brain associated with inflammation and higher rates of cell death. "Amyloid plaque is the main cause of Alzheimer's disease, and THC in particular is very good for removing [it]," says Mike Hart, family physician and medical director at the Ontario-based Ready to Go Clinic.
Hart points out that rodent studies have found a significant link with reduced amyloid plaque, due to the fact that THC inhibits the enzyme AChE, which is involved in producing the plaque. But while it might help to stop the plaque from forming in the first place, can it actually help reverse the onset of, say, dementia further down the road?
"'Reverse' would be a strong word to use," Hart cautions. "But CBD has been shown to promote neurogenesis, and we do have evidence in animal models that CBD can be effective for improving and reversing neurodegenerative diseases." Lack of large-scale human controlled trials, however, prevent most physicians from writing a cannabis prescription for someone suffering from a neurodegenerative disease.
The two most-studied cannabinoids are THC (tetrahydrocannabinol) and CBD (cannabidiol). While THC is the principle psychoactive compound (it gets you high), CBD has also been linked to many potential benefits.
"CBD not only has significant therapeutic potential, but it appears to mitigate the potentially adverse effects of THC," Kossen says. "CBD is like THC's responsible twin. It looks out for you and makes sure you get home safely. If you're going to enjoy ganja, avoid strains that are super high in THC and don't have CBD—instead, use strains with moderate THC content and at least one percent CBD." According to researchers at London's King's College, weed that's very high in THC—skunk weed—is significantly more likely to induce psychosis after prolonged use than the regular stuff, which typically has a higher ratio of CBD to THC. Look for a ratio closer to 1:5 or even 1:1 if you can get it.
Several animal studies have shown that both THC and CBD inhibit the growth of amyloid plaque, a major cause of several neurodegenerative disorders. We also know THC and CBD can help a lot of humans manage the symptoms of these disorders. "If you have a neurodegenerative disease like Parkinson's, for example, a lot of patients have trouble sleeping," Hart says. "Using a little THC at night can help them fall asleep faster and stay asleep longer. And then during the day, you can use a little bit of CBD, which may help decrease the movements that are produced by some people who have Parkinson's disease."
But some doctors are concerned that this can lead to people thinking they can simply devour a tray of pot brownies to manage a disorder. "With Alzheimer's, dosage is everything," says Paul Rosenberg, a geriatric psychiatrist at Johns Hopkins Hospital. "The preparations they're selling in places like Colorado are very, very strong. I'm giving my Alzheimer's patients 10 milligrams of cannabinoids and in Colorado you'll find a candy bar that says 100 milligrams and probably gives you more."
Yes, this also means that if you don't like to smoke, edibles—and most other methods of delivery—are a perfectly safe alternative. "There are lots of ways to administer cannabinoids that don't involve smoking pot," says Mark Ware, a professor of family medicine and anesthesia at McGill University and executive director for the Canadian Consortium for the Investigation of Cannabinoids. "You can take them orally, topically, rectally, and plenty of other ways."
But there's an important point to note: While THC and CBD are the most-studied cannabinoids, there are 111 others in marijuana, many of which could have medicinal uses if resources are committed to studying them. THC-B, for instance, has been linked to decreased appetite and improved insulin sensitivity. (Season 5, episode 8 of HBO's Vice took a closer look at a strain high in THC-B that was found in the Congo.)
So there's reason to believe that THC and CBD could help reduce plaques, a major cause of several neurodegenerative disorders. And we know they can help manage symptoms of these disorders. What we'd like to know is exactly what that means for humans in terms of preventing them. "Things like stroke, spinal cord injury, concussion, traumatic brain injury—all of these are nerve-injury conditions where cannabinoids could be looked at as having potentially neuro-sparing effects," Ware says. "And then you get into neurodegenerative conditions like Alzheimer's and dementia, where there's a good rationale to be looking at those as well."
Right now we have suggestive evidence from animal models, a lot of anecdotal evidence from patients, and due to the changing legal landscape in North America (particularly Canada) we have more access to purified, standardized, and quality-controlled cannabinoids to use in clinical research. But studies on prevention are timely and expensive.
"I think there's promise, but it's much too early to say until the studies move forward whether that's going to translate into meaningful therapies for humans," Ware says. "But it's certainly well worth doing."
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