A study published in the July issue of the Journal Anesthesiology discovered that oral cannabis (a form of medical marijuana) not only failed to alleviate certain types of pain in human volunteers but, surprisingly, it instead caused increased sensitivity to some forms of pain.
In their research, Birgit Kraft, M.D., and her colleagues from the Medical University of Vienna evaluated the analgesic potency of orally administered cannabis extract that included its main psychoactive component, Tetrahydrocannabinol (THC).
"The surprising result of our study was the absence of any kind of analgesic activity of THC-standardized cannabis extract on experimentally induced pain using well-established human model procedures," said Dr. Kraft. "Our results also seem to support the impression that high doses of cannabinoids may even cause increased sensitivity in certain pain conditions."
In Dr. Kraft's study, 18 healthy female volunteers were given oral cannabis extract or active placebo and then evaluated for heat and electrical pain thresholds in skin areas of experimentally induced sun burn, an accepted approach to assessing responses to acute pain.
Previous studies have suggested that cannabis and THC may be effective in treating chronic pain, such as in cancer patients, patients with spinal cord injury, or those with multiple sclerosis. And, though inconsistent, some studies on patients with acute pain have suggested beneficial effects
Consistent with the uncertainty about oral cannabis ingestion evaluated in this study, there is also uncertainty in the research community as to whether inhaled cannabis might prove more efficacious for pain relief than orally ingested cannabis.
Dr. Kraft's results concerning oral cannabis for acute pain were seemingly conclusive. "From comparisons with previous clinical data, the lack of pain relief from the cannabis dosage and oral administration in our study cannot be considered the result of inadequate dosage or insufficient gastrointestinal absorption," said Dr. Kraft. "The high levels of THC detected in the blood of our subjects as well as the occurrence of typical THC side effects argue for sufficient availability, and thus we draw the conclusion that THC was not effective in treating acute pain."
Dr. Kraft stressed, however, that cannabis may still remain a viable option for certain types of chronic pain patients.
"Pain is a very complex and subjective phenomena," she said. "Chronic pain has not only been shown to lead to changes in peripheral and central neuronal processing, but also to be associated with psychosocial problems, physical disorders, and functional disabilities. Recent studies have indicated that cannabis can be effective in treating certain types of chronic pain and helping patients to cope by improving quality of life."
Dr. Kraft and her colleagues concluded that contemporary treatment strategies that rely on experimentally proven therapies still remain the best option for most patients suffering acute pain.
"In patients with acute pain, other analgesic drugs such as narcotics and non-steroidal anti-inflammatory drugs (NSAIDs) produce more reliable and potent analgesia," she said.