Chronic pain and posttraumatic stress disorder are among the top reasons given by patients seeking medical marijuana in states where it is legal, but there is little scientific evidence to support its value for treating either condition, based on the results of a pair of systemic evidence reviews conducted by the U.S. Department of Veterans Affairs.
The findings were published online Aug. 14 in the Annals of Internal Medicine.
In the PTSD study, Maya E. O’Neil, PhD, of the VA Portland (Ore.) Health Care System, and colleagues found no significant evidence to support the effectiveness of cannabis for relieving symptoms (). The researchers reviewed data from two systematic reviews and three primary studies.
One of the larger studies (included in one of the systematic reviews) included 47,000 veterans in VA intensive PTSD programs during 1992-2011. In fact, after controlling for demographic factors and other confounding variables, individuals who continued to use cannabis or started using cannabis showed worse PTSD symptoms than did nonusers after 4 months.
“Findings from [randomized, controlled trials] are needed to help determine whether and to what extent cannabis may improve PTSD symptoms, and further studies also are needed to clarify harms in patients with PTSD,” the researchers noted.
In the review of chronic pain literature, Shannon M. Nugent, PhD, also of the VA Portland (Ore.) Health Care System, and her colleagues examined 27 trials, 11 reviews, and 32 primary studies ().
“Across nine studies, intervention patients were more likely to report at least 30% improvement in pain,” the investigators said. But this finding was specific to tetrahydrocannabinol (THC), the researchers said, and evidence of the ability of cannabis to relieve other types of pain, such as cancer pain and multiple sclerosis pain, was insufficient.
In addition, the researchers found a low strength of evidence association between cannabis use and the development of psychotic symptoms, and a moderate strength of evidence association between cannabis use and impaired cognitive function in the general population. “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” they said.
Although no significant differences were noted in rates of adverse events between cannabis users and nonusers, some data suggested users had an increased risk for short-term adverse events that ranged from dizziness to paranoia and suicide attempts.
Other potential harms associated with cannabis use included decreased lung function, increased risk of complications from infectious diseases, cannabis hyperemesis syndrome, and increased risk of violent behavior.
“Even though we did not ﬁnd strong, consistent evidence of benefit, clinicians will still need to engage in evidence-based discussions with patients managing chronic pain who are using or requesting to use cannabis,” the researchers wrote.
The researchers had no financial conflicts to disclose. The study was commissioned by the Veterans Health Administration.