Higher marijuana intake increases pain

28 October, 2007

Though smoking marijuana, or cannabis, in moderate doses helps reduce pain, the pain increases at high doses.

A new study, published in the latest issue of the journal Anesthesiology, stresses that marijuana reduces pain only within a smaller dose range.

Dr Mark S Wallace, of the University of California, San Diego, the United States, and lead author of the study, said that the study suggests that there is a therapeutic window for analgesia, with low doses being ineffective, medium doses resulting in pain relief and high doses increasing pain.

Dr Wallace and colleagues assessed the effects of smoking marijuana on pain responses in 15 healthy volunteers. On different days, the research subjects smoked low, medium, or high doses of cannabis (based on the content of 9-delta-tetrahydrocannabinol, the main active chemical in marijuana), or an inactive placebo.

Pain was induced in the healthy volunteers by injecting capsaicin, the “hot” chemical found in chili peppers, into the skin. (Capsaicin injection is a standard technique used in pain studies, according to the authors of the study).

Five minutes after smoking, none of the three doses of cannabis had any effect on pain responses to capsaicin.

However, 45 minutes after smoking the moderate dose of cannabis, pain was significantly reduced – about 6 points lower on a 100-point scale, compared with the inactive placebo.

In contrast, 45 minutes after smoking the high dose of cannabis, pain scores were increased – about 8 points higher than with placebo.

The low dose of cannabis was found to have no effect on pain scores. None of the three doses affected the spread of pain beyond the area injected with capsaicin.

Levels of tetrahydrocannabinol measured in the blood were significantly related to reduced pain scores at the moderate dose of cannabis, but not to the increase in pain with high-dose cannabis. The volunteers’ sense of feeling “high” increased with each dose of cannabis, even though the pain-relieving effects did not, the study found.

According to Dr Mark S Wallace, with several states in the United States having passed laws legalizing the medical use of cannabis, there has been a call for more research on medicinal cannabis.

Dr Wallace and colleagues have called for further research, including studies of the clinical value of the pain-reducing effects of cannabis.

However, Dr Wallace added, based on this study’s findings, he would not recommend marijuana as a method of pain reduction at this time.






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