A study by American researchers suggests that smoking a moderate amount of cannabis (marijuana) may relieve pain but smoking high doses may increase pain.
According to the researchers at the University of California in San Diego their study is the first to use a dose-response method and they say it was found that cannabis has a 'therapeutic window' with moderate doses decreasing pain and high doses increasing pain.
Lead investigator Dr. Mark Wallace says previous studies have suggested that smoked cannabis increases pain so they studied the effect of low, medium and high doses of smoked cannabis on a group of 15 healthy volunteers.
The volunteers who smoked either cannabis or a placebo were subjected to an injection of capsaicin, the spicy substance found in chili peppers, into the forearm in order to induce the pain, five and 45 minutes after drug exposure.
Wallace and his colleagues found that 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, while no such effect was seen with the low dose.
The researchers do however emphasise that no conclusions on the pain-relieving efficacy of smoked cannabis can be made from this study regardless of their findings and they say more research is needed.
The study is published in this month's issue of the journal Anesthesiology.