"Previous studies have suggested that smoked cannabis increases pain," lead investigator Dr. Mark Wallace of the University of California, San Diego told Reuters Health. "This is the first study using a dose-response method that suggests smoked cannabis has a therapeutic window with moderate doses decreasing pain and high doses increasing pain."
In a group of healthy volunteers, Wallace and colleagues studied the effect of low, medium and high doses of smoked cannabis or placebo on pain induced by injecting capsaicin into the forearm 5 and 45 minutes after drug exposure.
No dose of cannabis had any effect at 5 minutes, but by 45 minutes after exposure there was a significant decrease in pain with the medium dose and a significant increase in pain with the high dose. No such effect was seen with the low dose.