Substantial evidence suggests cannabis use is associated with the development of psychoses and schizophrenia, but studies also show that the substance may have benefits, including alleviating chronic pain and chemotherapy-induced nausea, according to a wide-ranging new report on the benefits and harms of cannabis from the National Academies of Sciences, Engineering, and Medicine (NAS).
When asked whether the NAS committee's report might be seen as a green light for America's cannabis users, panel member Sean Hennessy, PharmD, PhD, said, "We tried our best to provide objective answers, and people will use that information however they use that information."
The report, which contains 100 evidence-based conclusions about cannabis, including the products derived from it, calls for the removal of barriers that prevent scientists from gaining a broader understanding of the widely used substance. Among the chief barriers cited is that marijuana is a Schedule I substance.
The NAS committee said that this designation "impede[s] the advancement of cannabis and cannabinoid research," but it did not call for a change in scheduling. That was not part of its mandate, said Dr Hennessy, professor of epidemiology at the Perelman School of Medicine, University of Pennsylvania, in Philadelphia, told reporters attending a press briefing.
Committee members said more guidance is needed, especially as 22 million Americans older than 12 years report current cannabis use ― the majority for recreational purposes. Twenty-eight states and Washington, DC, have legalized marijuana for medical use, and eight states and the District of Columbia allow recreational use.
"This growing acceptance, accessibility, and use of cannabis and its derivatives have raised important public health concerns," said NAS committee chair Marie McCormick, MD, ScD, the Esther Feldberg Professor of Maternal and Child Health at Harvard's T. H. Chan School of Public Health, Boston, Massachusetts.
Dr McCormick said the lack of research means that users have no information on appropriate, useful, or safe levels of cannabis.
"Developing data for patients and medical practitioners should be a high priority," said Dr Hennessy.
The Health Effects of Cannabis and Cannabinoids: Current State of Evidence and Recommendations for Research is the NAS' first comprehensive report on marijuana since 1999.
In compiling the report, the NAS committee weighed more than 10,000 relevant abstracts, giving highest preference to systematic reviews conducted from 2011 to 2016, and "high quality primary research" that focused on 11 health endpoints: therapeutic effects; injury and death; cancer; heart attack, stroke and diabetes; respiratory disease; immunity; mental health; problem cannabis use; cannabis use and the abuse of other substances; psychosocial issues; and prenatal, perinatal, and neonatal exposure.
The committees' conclusions were assigned five levels of evidence. Causation was not part of the picture.
"In some cases, we discuss possible reasons for the association, but in the vast majority of cases, those statistical associations are just that – associational, not causal," said panel member Sachin Patel, MD, PhD, associate professor of psychiatry at Vanderbilt University School of Medicine, Nashville, Tennessee.
Mental Health Effects
The evidence shows that cannabis use is likely to increase the risk of developing schizophrenia, other psychoses, and social anxiety disorders, and to a lesser extent depression, but "there is little information about causality," noted Dr Patel.
The committee found moderate evidence of increased mania symptoms and hypomania in patients with bipolar disorder who use cannabis regularly, and there was evidence of an increase in the incidence of suicidal ideation and suicide attempts with heavy use.
It also reported substantial evidence linking greater frequency of cannabis use and an increased likelihood of developing problem cannabis use, and that initiating cannabis use at a younger age increases the likelihood of problem use.
The evidence linking cannabis use and abuse of other substances was "moderate."
The data were strongest in support of cannabis' beneficial effects in relieving chronic pain and chemotherapy-induced nausea and vomiting and improving symptoms of multiple sclerosis spasticity. For these conditions, "there is good quality evidence that some patients obtain substantial relief from either cannabis or cannabis-based products," said Dr Hennessy.
The substance may also be effective for improving short-term sleep in patients with obstructive sleep apnea, fibromyalgia, chronic pain, and multiple sclerosis, and possibly for improving anxiety symptoms and increasing appetite and decreasing weight loss in HIV and AIDS patients.
The evidence is insufficient as to whether cannabis is effective for a host of other conditions, including cancer, irritable bowel syndrome, epilepsy, amyotrophic lateral sclerosis symptoms, or spinal cord injury–related spasticity, said the report.
Cannabis may pose risks, including a worsening of respiratory symptoms and more frequent bronchitis with long-term smoking, an increase in motor vehicle accidents, and low birth weight in offspring of maternal smokers. The committee also found an increased risk for cannabis overdose in children in states where the substance is legal.
The NAS panel urged the federal government to step up its efforts to determine cannabis' potential benefits and harms. Among its recommendations: that public health agencies join with philanthropic and professional organizations, private companies, and clinical and public health research groups to provide funding and support for a national cannabis research agenda.
The committee also urged federal health agencies to fund a workshop to create research standards and benchmarks "to guide and ensure the production of high-quality cannabis research" and to engage in more surveillance of cannabis use to better determine how and when Americans use pot and what the exposures might mean in the short and long term.
Finally, the government should convene a committee that can help determine how best to advance cannabis research, in part, by addressing regulatory barriers, said the panel.
The study was sponsored by Alaska Mental Health Trust Authority, the Arizona Department of Health Services, the California Department of Public Health, the Centers for Disease Control and Prevention (CDC), the CDC Foundation, the US Food and Drug Administration, the Mat-Su Health Foundation, the National Highway Traffic Safety Administration, the National Institutes of Health National Cancer Institute, the National Institutes of Health National Institute on Drug Abuse, the Oregon Health Authority, the Robert W. Woodruff Foundation, the Colorado Health Foundation, the Truth Initiative, and the Washington State Department of Health.