The idea of medical use of marijuana for pain relief has been thrown into doubt after researchers have found that active ingredients in marijuana can instead spread and prolong pain.
The team of researchers from University of Texas Medical Branch at Galveston, has found that a group of compounds in marijuana called the cannabinoids prolong pain rather than damping it down.
"In the spinal cord there's a balance of systems that control what information, including information about pain, is transmitted to the brain," said UTMB professor Volker Neugebauer, one of the authors.
"Excitatory systems act like a car's accelerator, and inhibitory ones act like the brakes. What we found is that in the spinal cord endocannabinoids can disable the brakes," Neugebauer added.
The researchers used the spinal cords of mice to determine the inhibitory effect of endocannabinoids on pain.
They found that after applying a biochemical that mimics an endocannabinoid to nerve cells, there was a response to pain. When they studied the spinal cord of mice that lacked receptors for endocannabinoids, they found the pain response was blocked.
The research team including Neugebauer, senior research scientist Guangchen Ji and collaborators from Switzerland, Hungary, Japan, Germany, France and Venezuela has found that endocannabinoids in the spinal cord suppress the body's ability to put "the brakes" on pain signals, leaving the gates wide open.
"To sum up, we've discovered a novel mechanism that can transform transient normal pain into persistent chronic pain," said Neugebauer.
"Persistent pain is notoriously difficult to treat, and this study offers insight into new mechanisms and possibly a new target in the spinal cord," Neugebauer added.
The study also raises questions about the efficacy of marijuana in relieving acute pain.
The study is published in journal Science.