In an University of California, San Diego (UCSD) Center for Medical Cannabis Research (CMCR) study, due to be published in the November journal of Anesthesiology, reports that cannabis in too high or too low of dosage provides little, if any benefit.

Healthy volunteers were given a placebo cigarette or a marijuana cigarette that contained either 2%, 4%, or 8% delta-9-tetrahydrocannabinol (THC) by weight. The subjects’ skin was first exposed to the irritant capsaicin, an alkaloid derived from hot chili peppers. The irritant mimics the type of neuropathic pain experienced by patients with HIV/AIDS, diabetes, or shingles–a brief, intense pain followed by a longer-lasting secondary pain.

The analgesic effects of the cannabis took about 45 minutes before it had an impact on the pain. The results showed cannabis does have a therapeutic value at a medium-dose level (4% THC by weight). The low and higher dosages (2% & 8% THC by weight) were not as beneficial. It was suggested that the less-effective higher dosage of THC is something seen among other medications, such as antidepressants.

A large scale study is needed to measure the efficacy of cannabis, the researchers note. Medical marijuana could play an important role in treating patients who don’t respond well to the usual pain relievers or can not tolerate drugs such as ibuprofen or opioids used for severe pain.

The study was funded by a California state initiative passed in 1999 for rigorous study of the safety and efficacy of medicinal cannabis in treating diseases.