"This study used an experimental model of neuropathic pain to determine whether pain induced by the injection into the skin of capsaicin, a compound which is the 'hot' ingredient in chili peppers, could be alleviated by smoked cannabis. Another aim of the study was to examine the effects of 'dose' of cannabis, and the time course of pain relief. In a randomized double-blinded placebo controlled trial, volunteers smoked low, medium, and high dose cannabis (2%, 4%, 8% THC by weight) or placebo cigarettes.
"The full results of this study were published in the journal Anesthesiology (Wallace, et al., 2007 – see reference list). Nineteen healthy volunteers were enrolled, and 15 completed all four smoking sessions. In brief, five minutes after cannabis exposure, there was no effect on capsaicin-induced pain at any dose. By 45 minutes after cannabis exposure there was a significant decrease in capsaicin-induced pain with the medium dose (4%) and a significant increase in pain with the high dose (8%). There was no significant effect seen with low dose (2%). There was a significant inverse relationship between pain perception and plasma THC. In summary, this study suggested that there may be a 'therapeutic window' (or optimal dose) for smoked cannabis: low doses were not effective; medium doses decreased pain; and higher doses actually increased pain. These results suggest the mechanism(s) of cannabinoid analgesia are complex, in some ways like non-opioid pain relievers (e.g., aspirin, ibuprofen) and in others like opioids (e.g., morphine)."
Center for Medicinal Cannabis Research, "Report to the Legislature and Governor of the State of California presenting findings pursuant to SB847 which created the CMCR and provided state funding," University of California, (San Diego, CA: February 2010), pp. 11.