Limited evidence available to determine effectiveness and safety of cannabis to treat chronic pain

1. There is some evidence that cannabis reduces neuropathic pain, but there is inadequate evidence for other pain types.

2. Possible harms of cannabis use include higher collision risk with acute cannabis intoxication, short-term cognitive impairment in long-term active cannabis users, and increased risk of developing psychotic symptoms.

Evidence Rating Level: 1 (Excellent)       

Study Rundown: The District of Columbia and 28 states have legalized cannabis for medical purposes, and 45%–80% of people seeking cannabis for this purpose are doing so to manage pain. Although physicians may need to discuss with their patients the possible benefits and harms of cannabis use, there is limited information about this. This systematic review of intervention trials and observational studies sought to evaluate the benefits and harms of cannabis use for treating chronic pain. There is some evidence that cannabis reduces neuropathic pain, but there is inadequate evidence for other types of pain. In the general population, there is some evidence suggesting there is an association between cannabis use and a higher risk of adverse effects on mental health. No strong, consistent evidence of benefits was found. Physicians should understand the potential harms of cannabis use to enable them to have evidence-based discussions with patients who have chronic pain and are using or seeking to use cannabis to manage their pain.

A strength of the study is that 13 674 titles and abstracts were reviewed to identify as much relevant data as possible. Limitations of the study include the lack of rigorous trials; the cannabis formulations examined may not be representative of what is available commercially; and the limited ability to apply the data to the elderly, the chronically ill, and heavy cannabis users.

Click to read the study, published in Annals of Internal Medicine

Relevant Reading: The effect of medicinal cannabis on pain and quality-of-life outcomes in chronic pain: A prospective open-label study

In-Depth [systematic review]: This study used MEDLINE, PubMed, Embase, Evidence-Based Medicine Reviews, PsycINFO, and gray literature sources from the start of the database through March 2017. Researchers included 13 systematic reviews and 62 primary studies in their analysis. Low-strength evidence from 27 chronic pain trials suggests that cannabis may reduce neuropathic pain, but there is insufficient evidence for other pain types. Based on combined data from 11 systematic reviews and 32 primary studies, harms in the general population from cannabis use include a moderately higher risk of collision with acute cannabis intoxication (moderate-strength evidence), a link between using cannabis and developing psychotic symptoms (low-strength evidence), and a possible association between long-term cannabis use and small to moderate short-term cognitive impairment in active users (moderate-strength evidence).

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