Smoked cannabis eased pain induced in healthy volunteers, according to a study by researchers at the University of California, San Diego Center for Medical Cannabis Research.

However, the researchers found that less may be more.

In the placebo controlled study of 15 subjects, a low dose of cannabis showed no effect, a medium dose provided moderate pain relief, and a high dose increased the pain response.

The study used capsaicin, an alkaloid derived from hot chili peppers that is an irritant to the skin, to mimic the type of neuropathic pain experienced by patients with HIV/AIDS, diabetes or shingles – brief, intense pain following by a longer-lasting secondary pain.

The subjects 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.)

“Interestingly, the analgesic effect wasn’t immediate; it took about 45 minutes for the cannabis to have an impact on the pain,” said Igor Grant, M.D., F.R.C.P.(C), professor and Executive Vice-Chair of the Department of Psychiatry, the director of the CMCR.

The results, showing a medium-dose (4% THC by weight) of cannabis to be an effective analgesic.

“This study helps to build a case that cannabis does have therapeutic value at a medium-dose level,” said Grant. “It also suggests that higher doses aren’t necessarily better in certain situations – something also observed with other medications, such as antidepressants.”

The researchers stated that more and larger studies need to be conducted to measure the efficacy of cannabis, noting that medical marijuana could play an important role in treating patients who don’t respond well to the usual pain relievers or can’t tolerate drugs such as ibuprofen or opioids used for severe pain.