Study: Little to no evidence cannabis alleviates chronic pain

A new review of nearly 14,000 research articles and studies has found there is little to no evidence that cannabis alleviates chronic pain in adults.

The full report, funded by the U.S. Department of Veterans Affairs Quality Enhancement Research Initiative and published Aug. 15 in the Annals of Internal Medicine, is found here.

Highlights from the report’s findings

Title: The Effects of Cannabis Among Adults With Chronic Pain and an Overview of General Harms: A Systematic Review

Background: Cannabis is increasingly available for the treatment of chronic pain, yet its efficacy remains uncertain.

Purpose: To review the benefits of plant-based cannabis preparations for treating chronic pain in adults and the harms of cannabis use in chronic pain and general adult populations.

Data Sources: MEDLINE, Cochrane Database of Systematic Reviews, and several other sources from database inception to March 2017.

Study Selection: Intervention trials and observational studies, published in English, involving adults using plant-based cannabis preparations that reported pain, quality of life, or adverse effect outcomes.

Data Extraction: Two investigators independently abstracted study characteristics and assessed study quality, and the investigator group graded the overall strength of evidence using standard criteria.

Data Synthesis: From 27 chronic pain trials, there is low-strength evidence that cannabis alleviates neuropathic pain but insufficient evidence in other pain populations. According to 11 systematic reviews and 32 primary studies, harms in general population studies include increased risk for motor vehicle accidents, psychotic symptoms, and short-term cognitive impairment. Although adverse pulmonary effects were not seen in younger populations, evidence on most other long-term physical harms, in heavy or long-term cannabis users, or in older populations is insufficient.

Limitation: Few methodologically rigorous trials; the cannabis formulations studied may not reflect commercially available products; and limited applicability to older, chronically ill populations and patients who use cannabis heavily.

Funding Source and Role: The U.S. Department of Veterans Affairs Quality Enhancement Research Initiative supported the review but had no role in the design and conduct of the study; collection, management, analysis and interpretation of the data; preparation, review, and approval of the manuscript; or decision to submit the manuscript for publication.

Conclusion: Limited evidence suggests that cannabis may alleviate neuropathic pain in some patients, but insufficient evidence exists for other types of chronic pain. Among general populations, limited evidence suggests that cannabis is associated with an increased risk for adverse mental health effects.

Investigators: Shannon M. Nugent, PhD; Benjamin J. Morasco, PhD; Maya E. O’Neil, PhD; Michele Freeman, MPH; Allison Low, BA; Karli Kondo, PhD; Camille Elven, MD; Bernadette Zakher, MBBS; Makalapua Motu’apuaka, BA; Robin Paynter, MLIS; Devan Kansagara, MD, MCR

Mental Health and Cognitive Harms in the General Population

One systematic review and 8 studies consistently found an association between cannabis use (specifically related to THC content) and the development of psychotic symptoms (low strength of evidence) (Table 3). The association was seen both in populations at risk for psychotic spectrum disorders and in average-risk populations. The possibility that cannabis contributes directly to the development of psychotic symptoms is supported but not proved by biological plausibility, evidence of a dose–response relationship, prospective cohort studies, and small experimental studies.

A systematic review of 6 longitudinal studies provides low-strength evidence of an association between cannabis use and exacerbation of manic symptoms in patients with known bipolar disorder. The review found higher incidence of new-onset mania symptoms among populations without a diagnosis of bipolar disorder (pooled odds ratio, 2.97 [CI, 1.80 to 4.90]).

Two systematic reviews of studies in general populations provide moderate-strength evidence that active, long-term cannabis use is associated with small to moderate negative effects on many domains of cognitive function, but evidence on cognitive effects in past users is insufficient.

A meta-analysis of 4 epidemiologic studies found significantly increased odds of suicide death (pooled odds ratio, 2.56 [CI, 1.25 to 5.27]) with any cannabis use. However, our confidence in the findings is limited by inconsistent findings among included studies, inadequate assessment of exposure, and inadequate adjustment for confounding among the studies (insufficient strength of evidence).