The scientific evidence is too limited to make firm conclusions about the effectiveness and safety of cannabis and cannabinoid products in treating chronic pain or post traumatic stress syndrome (PTSD). The results of two systematic evidence reviews from the U.S. Department of Veterans Affairs (VA) are published in Annals of Internal Medicine.

Currently, medical marijuana is legal in 28 states and the District of Columbia and up to 80 percent of persons who seek medicinal cannabis do so for pain management. While the use of medicinal cannabis has become increasingly accepted, there is little comprehensive and critically appraised information about the benefits and harms of using it to treat chronic pain.

Researchers reviewed data from 27 chronic pain trials to determine the benefits and harms of cannabis preparations for treating chronic pain in adults. They found low-strength evidence that cannabis alleviates neuropathic pain but there was insufficient evidence to draw conclusions about the use of medical marijuana for other types of pain. The researchers found sufficient evidence to conclude that cannabis use among the general population could increase risk for harms, including motor vehicle accidents, psychotic symptoms, and short-term cognitive impairment. There was insufficient evidence to determine the risks for other types of harms associated with heavy or long-term cannabis use or in older populations.

Plant-based Cannabis for PTSD

More than one-third of patients seeking cannabis for medical purposes in states where medicinal marijuana use is legal list PTSD as the primary reason for their request. However, there is little scientific evidence available for determining the benefits and harms of cannabis use for treating PTSD.

Researchers reviewed data from 2 systematic reviews and 3 primary studies assessing the benefits and harms of plant-based cannabis preparations (not synthetic cannabinoids) in treating PTSD in adults. They found that evidence was insufficient to draw firm conclusions about the efficacy of cannabis in this patient population, but one of the largest observational studies of veterans with PTSD found small but significant worsening of symptoms in patients who continued or started cannabis use compared with patients who had never used or stopped using cannabis during the study.

The author of an accompanying editorial from Vanderbilt Psychiatric Hospital writes that these findings largely echo the findings of other respected organizations and suggest a growing consensus in the field. Little high-quality evidence exists from which to draw firm conclusions about the efficacy of cannabis and cannabinoid products for treating pain and PTSD. Regardless of the research gaps, states are unlikely to remove medical indications from legislation. Practicing physicians must learn what they can about cannabis, educate their patients, and make recommendations based on the science.

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