Marijuana's painkilling properties are being called into question by new research that suggests the drug can amplify and prolong pain rather than relieve it.
A study published in the current issue of Science suggests prescribing marijuana for pain relief, which is legal in a number of countries, including Canada, may be counterproductive.
Experiments with rodents and humans found that a group of compounds that includes cannabinoids, the active ingredients in marijuana, can interfere with the body's mechanisms to stop pain signals from reaching the brain.
"If you had a toothache, you probably wouldn't want to treat it with marijuana, because you could actually make it worse," said University of Texas professor Volker Neugebauer, one of the study's authors.
"Now, for more pathological conditions like neuropathic pain, where the problem is a dysfunction within the nerves themselves and a subsequent disturbance throughout the nervous system that's not confined to the pain system, marijuana may be beneficial."
Health Canada allows those suffering from grave and debilitating illnesses to access marijuana for medical use to treat severe pain from conditions such as multiple sclerosis, spinal cord injury, cancer, arthritis and HIV/AIDS.
Researchers from the United States, Switzerland, Hungary, Japan, Germany, France and Venezuela collaborated on the new research. They found that endocannabinoids in the spinal cord suppress the body's ability to put "the brakes" on pain signals, leaving pain with a straight road to the brain.
"In the spinal cord there's a balance of systems that control what information, including information about pain, is transmitted to the brain," Prof. Neugebauer said.
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