Cannabinoids, compounds commonly found in the marijuana plant, may lessen anticipatory nausea--which occurs when people associate a place or taste with expected intestinal distress, said Linda Parker, PhD, a psychology professor at Canada's Wilfrid Laurier University, at APA's 2004 Annual Convention in Honolulu. Anticipatory nausea often occurs in patients undergoing chemotherapy and can result in them feeling nauseous before even receiving treatment, she noted.
"Anticipatory vomiting is a disturbing effect for many people," explained Parker. "The cues of the hospital, the situation in which the chemotherapy occurs, become associated with the emetic effects of the drug--and serotonin-antagonists [commonly prescribed antinausea drugs] are ineffective in this if it develops."
In a study published in Integrative Physiological & Behavioral Science (Vol. 38, No. 2), Parker and her colleagues conditioned 94 rats to associate a sugary taste with nausea by squirting sucrose into the animals' mouths and then injecting them with the nausea-inducing chemical lithium-chloride.
The researchers then tested the nausea-suppressing properties of two primary cannabinoids found in marijuana, tetrahydrocannabinol (THC) and the nonintoxicating cannabidiol (CBD), by injecting one third of the animals with THC, one third with CBD and the rest with an inactive solution before exposing them to sucrose. As expected, the rats that associated sucrose with nausea, and did not receive a shot of CBD or THC, gaped--an expression of nausea in a species that does not vomit--after tasting the sugar. Those injected with the cannabinoids did not gape.
In a follow-up experiment, Parker and her colleagues injected some of the rats with CBD or THC before pairing the taste of sugar with the experience of nausea. The researchers found that animals pretreated with the drugs did not gape when re-exposed to the taste. These data suggest cannabinoids may be effective not only in reducing anticipatory nausea, but also in preventing patients from associating the hospital environment with intestinal discomfort to begin with, she noted.
Both CBD and THC seem to be similarly effective in preventing anticipatory nausea, said Parker, but only THC has the side effect of "mental clouding." Additionally, she noted, a combination of cannabinoids and traditional antiemetics may be especially powerful in combating both the acute and anticipatory nausea experienced by chemotherapy patients.