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News Release

July 28, 2006

Marijuana May Provide Nausea Relief to Chemo Patients, Prof Finds

A University of Guelph psychology professor has discovered that marijuana may help prevent anticipatory nausea – relief that many cancer chemotherapy patients can’t obtain from existing anti-vomit and anti-nausea drugs.

Linda Parker’s research was published in recent issues of the journal Physiology and Behavior.

Many chemotherapy patients vomit as they walk into their clinic in anticipation of their treatment because they know it will cause nausea. These symptoms can deter some patients from continuing with their recommended course of treatment, said Parker, a behaviour neuroscientist and Canada Research Chair who recently joined U of G’s faculty.

“Known antiemetic drugs aren’t effective in treating this learned nausea,” she said.

Medication can control vomiting in 60 to 70 per cent of chemotherapy patients, but most per cent still suffer from nausea. Because nausea is difficult to record or measure, scientists have had difficulty conducting research on non-human subjects.

Using rats and shrews (a mouse-like mammal), Parker has been able to determine how two compounds found in marijuana –– THC (the chemical that makes people feel high) and cannabidiol (CBD) –– can treat vomiting and nausea.

Rats and other rodents aren’t capable of vomiting, but they open their mouths as though they’re about to retch when they feel nauseated, she said. “Their gaping reaction lets us know exactly when they are feeling nauseated.”

Shrews, unlike rodents, have the ability to vomit, so using both creatures, Parker was able to determine both the anti-vomit and anti-nausea effectiveness of THC and CBD.

“Cannabidiol suppresses vomiting in shrews and nausea in rats, as does THC, but CBD isn’t intoxicating, so it may be possible to develop cannabinoid-based treatments that suppress vomiting and nausea without making people feel high.”

To conduct the study, Parker put the shrews and rats in a specific place and injected them with a drug that causes vomiting in the shrews and gaping in the rats. She repeated those steps a few times. When she put the mammals back in the same place without the drug, the shrew retched and the rat gaped, even though they didn’t have a toxin in their systems.

“If you use classic antiemetic drugs before the test, the shrew still retches and the rat gapes, but if you give them THC or cannabidiol, it suppresses these reactions, and that’s consistent with anecdotal evidence from humans,” she said.

“People report that if they smoke marijuana before they go for chemotherapy treatment, they don’t experience the anticipatory nausea or vomiting.”

Parker has been collaborating with discoverer of THC, Raphael Mechoulam, at the Hebrew University in Jerusalem. Mechoulam also discovered the natural chemical in the body that acts on the same brain receptor (cannabinoid receptors) responsible for marijuana making people high – the equivalent of endorphins for morphine. It’s called anandamide, now known as “the brain’s own THC,” and Parker is looking at the role it plays in nausea and vomiting.