This article was published 4/12/2017 (1388 days ago), so information in it may no longer be current.
Even if you've never used cannabis, you've probably heard of THC. Put simply, it's the chemical compound in marijuana that gets you high.
You might have also heard of CBD, another compound in cannabis.
THC and CBD belong to a class of chemical compounds called cannabinoids. Specifically, THC (short for delta-9 tetrahydrocannabinol) and CBD (cannabidiol) are phytocannabinoids, or plant cannabinoids, among more than 100 such compounds produced naturally by the cannabis plant.
There are also synthetic cannabinoids, created in laboratories, and endocannabinoids, neurotransmitters produced naturally by humans and many other species.
Cannabinoids interact with at least two different cannabinoid receptors in the human nervous system. This biological system of chemical compounds and receptors, called the endocannabinoid system, has been found to play a role in regulating important bodily functions ranging from appetite and memory to sleep and pregnancy.
Researchers have even discovered functioning endocannabinoid systems in primitive microorganisms, which underlines the biological importance of cannabinoids.
"We've kept this system in spite of massive evolutionary changes," said Dr. Mark Ware, an associate professor in family medicine and anesthesia at McGill University and the executive director of the Canadian Consortium for the Investigation of Cannabinoids, a non-profit medical research network.
"So why has it been preserved? Any system that's involved in the regulation of movement, appetite, pain, mood, you shrink that down to very basic organisms, something that gets you away from a noxious stimulus and gets you toward a food is probably likely to be helpful in survival."
The chemical structures of the plant cannabinoids CBD and THC were first identified by Israeli organic chemist Raphael Mechoulam and his colleagues in 1963 and 1964, respectively. They remain the best understood cannabinoids found in cannabis, said Ware.
"The others are found in much smaller quantities in the plant, and we're only just beginning to identify them and characterize them on any sort of scale where we can start putting them into research projects at the animal or human level," Ware said.
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Anecdotal claims about the potential benefits of THC and CBD abound, but only a handful of therapeutic uses has been approved by government regulators.
As far as regulators and the mainstream medical establishment is concerned, THC is an accepted treatment for nausea and vomiting, usually in the context of chemotherapy. THC has also been approved as an appetite stimulant, used for cancer and HIV/AIDS patients. A combination THC/CBD oronasal spray has been approved to reduce spasticity in multiple sclerosis patients, and CBD has been shown to have anticonvulsant properties that can benefit some epilepsy patients.
Ware said the medical and pharmaceutical establishment needs evidence from many more large-scale clinical studies before accepting the other potential uses of cannabinoids such as THC and CBD.
"There are dozens of diseases where there's exploratory evidence, but it's too soon to say 'What do we know,'" he said.
Part of the reason we know so little about the potential benefits of cannabinoids may be a cultural bias against cannabis in recent scientific research.
"You're going to get answers based on the questions you're asking," explained Steven Laviolette, a professor of neuroscience at the University of Western Ontario who has been studying cannabis for about 13 years.
"So if you're looking for the negative aspects, those are the ones you're most likely going to find. Whereas if you're looking for the positive health benefits, those are the ones you're going to be focusing on in your data as well."
That's not to say that cannabinoids are necessarily benign, though.
"There are reams of evidence suggesting that acute exposure to high levels of THC can induce psychosis, can induce memory and cognitive deficits, but you have to also consider the positive effects," said Laviolette.
Ware concurs that the strongest available scientific evidence shows THC can pose risks to adolescent users, but said it's too early to understand how that association works.
"(Those at risk from THC) are usually young, very early, heavy users, and teasing out the socio-cultural context of use — why are these young kids using cannabis that much that early? — all of those may also play a role in these neurodevelopmental issues," Ware said. "So it gets complex."
Even after THC and CBD are well-understood, there will still be more than 100 plant cannabinoids left to study. Cannabinoid researchers have their work cut out for them, considering the potential synergies and interactions between individual cannabinoids — not to mention the interactions between cannabinoids and terpenes, which are odorous organic compounds secreted by cannabis and many other plants.
"Because the list is so long, it's an incredibly daunting task. You can imagine how much energy and resources we need to go into testing all of these different ratios and combinations," said Laviolette. "Basically it's an infinite number of possibilities, virtually."
The good news is, cannabis legalization in this country could give Canadian scientists a chance to be world leaders in cannabinoid research. Ware describes legalization as a "game-changer."
"It means that we will have access to products and consumers who are doing this now legally, which means that we can actually get a better understanding of patterns of use, of types of products that are being used, it means we can track outcomes," Ware said.
"When it's an illegal substance, all of that information is very challenging to get access to."