But faced with opposition from lawmakers and community groups, their quest for medical marijuana has met with limited success. Now, researchers at Wilfrid Laurier University are probing deep inside the brain to see how it controls nausea with marijuana—and how certain parts of the brain can mimic the weed’s properties.
There is evidence that the cannabis plant has been used for hundreds of years in a variety of therapies, including suppressing nausea and vomiting. But it was only in 1964 that tetrahydrocannabinol (THC) was isolated as the major component that gives marijuana users a “high.” Twenty-five years later, the specific brain receptors for THC were identified.
“This discovery showed that the human brain has naturally occurring receptors for THC. And we now have considerable experimental evidence that shows these receptors play a role in suppressing nausea,” says Professor Linda Parker, a Canada Research Chair in Behavioural Neuroscience at Wilfrid Laurier University in Waterloo, Ontario.
These receptors in the brain are activated by a neurotransmitter called anandamide, “the brain’s own THC,” Parker says. Anandamide belongs to a group of chemicals called cannabinoids. THC is also a cannabinoid chemical that mimics the actions of anandamide. This means it binds to cannabinoid receptors and affects how the body functions in a number of ways.
“The whole area of medical marijuana research is very exciting.”
The high associated with marijuana is the best-known way that marijuana affects the body. It’s also a major stumbling block to its acceptance as an anti-nausea medicine. Anti-drug campaigners are uneasy with the idea of marijuana as medicine. And many patients who use marijuana to combat nausea dislike the high associated with it. Parker’s research with a cannabinoid called “cannabidiol,” which doesn’t deliver the high associated with marijuana use, could help medical marijuana gain wider acceptance.
“Dr. Parker found that the role of cannabinoids in the brain in preventing nausea is not the same as their role in the production of typical marijuana effects like causing a high. This may be of enormous clinical value,” says Professor Raphael Mechoulam, a professor at the Department of Medicinal Chemistry and Natural Products at Hebrew University of Jerusalem.
Mechoulam and Yehiel Gaoni are the researchers who isolated THC in marijuana in 1964. Mechoulam remains a world leader in the field of cannabis research. He is collaborating with Parker, and together they have filed a patent on cannabidiol, one of 60 cannabinoids found in marijuana. It is as prevalent as THC. Mechoulam has developed an inhalant form of cannabidiol that is currently being tested in clinical pain trials with arthritic patients.
Parker and her team are also looking at how nausea and vomiting are triggered in situations where a person anticipates a taste or sensation that has made them sick in the past.
Parker calls this phenomenon “anticipatory nausea.” It can make life very difficult for cancer patients and others undergoing aggressive treatments with links to nausea. Cases of patients experiencing nausea when going to clinics for follow-up visits, even when they know they won’t be receiving chemotherapy or other nausea-inducing medicine, are well documented. Parker’s lab work has showed that pre-treatment with low doses of THC can completely suppress anticipatory nausea. Parker says these findings are yet another example of the complex and wide-ranging role cannabinoids play in the human body.
“The whole area of medical marijuana research is very exciting. It has implications not just for anti-nausea drugs for cancer patients, but also for appetite stimulation for AIDS patients and pain relief in arthritis,” says Parker. “It has also been shown to play a role in suppressing the impact of neurotransmitters that trigger epilepsy and strokes.”
Being sick to your stomach is unpleasant and it can mean missing work and other day-to-day activities. But for people fighting cancer, chemotherapy-related nausea and vomiting are more than an inconvenience—they can make life miserable and threaten their recovery.
“In extreme cases, it can make people too weak to continue treatment,” says Cheryl Limebeer, a postdoctoral fellow at Wilfrid Laurier University’s Department of Psychology. Her research with Professor Parker is helping to unlock why we become nauseated and how to block this response.
Finding the answer could have a huge impact on the lives of ordinary Canadians. If current trends continue, according to the National Cancer Institute of Canada, 38 percent of Canadian women and 43 percent of men will develop cancer in their lifetime. Not all of these people will require chemotherapy. But for a variety of cancers, including leukemia, lymphoma, lung, and breast cancer, chemotherapy is likely to be used.
Researchers know that vomiting is a common protective reflex that expels toxins. The sensation of nausea serves as a warning in much the same way that pain does. The sensation usually tells a person to stop eating, drinking, or smelling something to avoid being sick. But chemotherapy patients don’t have the option to avoid what is making them sick, and vomiting doesn’t remove the perceived toxin. So patients can become trapped in a cycle of nausea and vomiting.
To complicate things for researchers, although nausea often occurs before vomiting, they can each can occur independently. This means drugs that are effective against vomiting may not necessarily relieve nausea, and drugs that are effective against nausea may not necessarily stop vomiting.
But medical marijuana could offer hope. Parker and her team are working on the endocannabinoid system, the naturally occurring chemicals in the body that mimic chemicals found in marijuana. Their work suggests that this system plays an important role in both nausea and vomiting—potentially great news for millions of cancer patients.
Marijuana has been used medicinally and recreationally for thousands of years. But in recent years, there has been an explosion of interest in medical marijuana that has been backed by top-ranked researchers around the world.
Linda Parker is writing a chapter in Professor Raphael Mechoulam's upcoming book, Cannabinoids as Therapeutics: Milestones in Drug Therapy. Toegther they have also filed a patent on cannabidiol, one of the chemicals in marijuana.
UK-based GW Pharmaceuticals is a world leader in developing prescription medicines derived from marijuana. The company is working with a variety of marijuana chemicals including cannabidiol, and is focusing on a range of health problems, from arthritis to nausea and migraines. The first medicine the company will likely bring to market is Sativex. It’s currently being assessed by the UK Medicines and Healthcare products Regulatory Agency and by Health Canada. If approved, it will be marketed in Canada by Bayer.
Parker’s research is supported by the Natural Sciences and Engineering Research Council of Canada, the Canadian Institute of Health Research, and the Canada Foundation for Innovation.
Read a CBC News overview of the marijuana debate in Canada.
Learn about Health Canada’s position on medical marijuana and related initiatives.
Find out more information on cannabinoids, visit the website of the International Cannabinoid Research Society.
Learn about commercial applications for medical marijuana.
Visit the website of the National Cancer Institute of Canada.