Chronic Pain: Herbal Cannabis Showed No Serious Adverse Effects After One-Year Use

Medical marijuana shows favorable safety profile.

There is not yet enough clinical evidence suggesting that cannabis is effective for self-management of pain.

Some short-duration trials have shown efficacy, whereas other studies have shown little improvement over placebo. Effective or not, however, cannabis continues to be widely used as a self-management strategy by patients with a wide range of symptoms and diseases.

A study in The Journal of Pain suggests that such use over a one-year period did not increase patients’ risk of serious adverse events. This was a prospective cohort study in Canada to describe safety issues among subjects with chronic non-cancer pain, with a participant base of 216 individuals with chronic pain.

A standardized herbal cannabis product (12.5% THC) was dispensed to eligible subjects for one year. Controls (215) were subjects with chronic pain from the same clinics who were not cannabis users. The median daily cannabis dose was 2.5 grams per day and subjects were advised to take the first dose in the evening, beginning with low doses and titrate upwards to maximum tolerated dose with an upper limit recommendation of 5 grams per day.

The primary outcome consisted of serious adverse events (SAEs) and non-serious adverse events (AEs). Secondary safety outcomes included pulmonary and neurocognitive function and standard hematology, biochemistry, renal, liver and endocrine function.

Secondary efficacy parameters included pain and other symptoms, mood, and quality of life. There was no difference in risk of SAEs (adjusted IRR=1.08, 95% CI=0.57—2.04) between groups, although medical cannabis users were at increased risk of non–serious AEs (adjusted IRR=1.73, 95% CI=1.41–2.13).

Most of the non-serious AEs were mild to moderate, including nervous system disorders and respiratory disorders.

“Quality-controlled herbal cannabis, when used by cannabis-experienced patients as part of a monitored treatment program over one year, appears to have a reasonable safety profile,” the study authors concluded. “Longer term monitoring for functional outcomes is needed.”

Furthermore, the analysis looked at the neurocognitive and pulmonary functioning of the patients, as well as functioning of major organs such as the liver. It also measured efficacy through visual analog scales and the McGill Pain Questionnaire. Compared to baseline, a significant reduction in average pain intensity over one year was observed in the cannabis group but not in controls. Another interesting finding was that neurocognitive function improved in both groups.

“This finding differs from that found in recreational users of cannabis where a meta-analysis of 15 studies investigating the effects of recreational cannabis use on neurocognitive performance suggested that long-term cannabis users performed significantly poorer on tests of memory and attention than short-term users,” the authors explained. “Caution should be exercised in interpreting these results to all medical cannabis use as patients in this study used a standardized, quality controlled herbal cannabis product with a reliable THC potency of 12.5%.”