The placebo controlled study, led by Mark Wallace, M.D., professor of anaesthesiology at UCSD School of Medicine and Program Director for the UCSD Centre for Pain Medicine, was conducted on 15 subjects.
In the study all the participants were healthy volunteers who inhaled either medical cannabis or a placebo after pain was induced.
The marijuana cigarettes were formulated under NIH supervision to contain either zero, two, four or eight percent delta-9-tetrahydrocannabinol (THC.)
In the research capsaicin, an alkaloid derived from hot chilli peppers that is an irritant to the skin, in order to ape the type of neuropathic pain experienced by patients with HIV/AIDS, diabetes or shingles, which is a brief, intense pain followed by a longer-lasting secondary pain, was used.
The analysis of the study showed that a low dose of cannabis had no effect on pain, while a medium dose provided moderate pain relief.
And, astonishingly, a high dose of cannabis increased the pain response.
Wallace said that the results suggested a "therapeutic window" for cannabis analgesia.
"Subjects reported a decrease in pain at the medium dose, and there was also a significant correlation between plasma levels of THC, the active ingredient in cannabis, and decreased pain," Igor Grant, M.D., F.R.C.P.(C), professor and Executive Vice-Chair of the Department of Psychiatry, the director of the CMCR said.
"Interestingly, the analgesic effect wasn't immediate; it took about 45 minutes for the cannabis to have an impact on the pain," he said.
Grant noted from the study that cannabis had healing value when taken in medium doses.
"This study helps to build a case that cannabis does have therapeutic value at a medium-dose level. It also suggests that higher doses aren't necessarily better in certain situations - something also observed with other medications, such as antidepressants," he said.
The study will be published in the November issue of the journal Anaesthesiology.