Last month, the National Academies of Science, Engineering, and Medicine (NASEM) released a major new report on the health effects of cannabis and its constituent compounds, based on a comprehensive assessment of research conducted since 1999. The National Academy of Medicine, formerly the Institute of Medicine (IOM), is a nonprofit organization of medical and health professionals whose reports provide independent research reviews and recommendations on pressing issues in the field. The Health Effects of Cannabis and Cannabinoids is its first report on the subject since 1999, when (as the IOM) the organization reached the conclusion that "accumulated data indicate a potential therapeutic value for cannabinoid drugs, particularly for symptoms such as pain relief, control of nausea and vomiting, and appetite stimulation."
The new report is based on reviews of research on both the cannabis plant itself and its constituents, but its conclusions are substantially similar to the 1999 report: While cannabis use, particularly smoked cannabis, poses some long-term health and safety risks, there is evidence that cannabis or cannabinoids can treat certain medical conditions, which include nausea and vomiting from chemotherapy, spasticity from multiple sclerosis, and pain.
However, most research to date on the therapeutic potential of cannabinoids has studied individual cannabinoid chemicals, especially delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). And while the full report is highly detailed and provides appropriate caveats for the limitations of the research, I have concerns that the report summary and press coverage may give the impression that the findings apply equally to the cannabis plant ("medical marijuana") and to the cannabinoid formulations that have undergone rigorous clinical trials. In addressing potential therapeutic benefits of the cannabis plant and its constituents, it is important to explicitly identify the cannabinoid tested to avoid mistakes such as ascribing the potential antiepileptic effects of CBD to "marijuana," which usually contains less than 1 percent of this cannabinoid.
Even the existing evidence on cannabis and cannabinoids for pain, rated as "strong" in the NASEM report, is based on research with limitations. For studies using the cannabis plant (5 total), the sample sizes were small, studies were short (with duration under 2 weeks, which is too short to assess effectiveness for chronic pain), and they were subject to problems with blinding. The strongest evidence comes from studies with isolated cannabinoid compounds (e.g., THC), not the whole plant. Nevertheless, there are modest but consistent positive findings reported for treating certain types of pain with cannabis, suggesting a promising area for further therapeutic development.
"Medical marijuana" that has any appreciable THC content may have notable adverse side effects, including impairment of judgment and motor function and the risk of addiction. Unfortunately, there are currently no consistent quality controls, no assurances that patients are informed about side effects, and unclear recommendations about dosing and route of administration. It is important for people to understand the range of effects produced by cannabis as they weigh the risks and benefits for treating their health conditions with products from state dispensaries.
Regarding long-term psychosocial and mental health risks of marijuana use, the report largely supports the conclusion that use during adolescence is associated with various adverse outcomes and that it is associated with increased risk of psychosis and psychotic disorder and can worsen symptoms of these disorders. The report also found that cannabis use is associated with an increased risk for developing substance dependence other than cannabis use disorder. However, it did not find evidence that cannabis use raises risk of depression, anxiety, or post-traumatic stress disorder (PTSD), and it found only moderate support for links between cannabis use and poor academic achievement and educational outcomes. The NIDA does not concur with the latter conclusion: While it is true that the available data cannot establish causality of these adverse outcomes, the statistical association is consistent, substantial, and dose-related, especially for early and heavy use.
Regarding physical health effects of marijuana use, the report found a lack of clear evidence for any link to heart attack or stroke and lack of an association with cancers of the lung, head, and neck. Our sister Institute, the National Cancer Institute, does not concur with the strength of that conclusion, since disentangling the effects of tobacco from cannabis can be challenging and some data do suggest that a link to these cancers may exist. The report did find a link to low birth weight in babies born to mothers who used cannabis while pregnant but insufficient evidence at this point to draw strong conclusions on other childhood outcomes of prenatal exposure.
The NIDA strongly agrees with the report’s finding that there are impediments to performing quality research on cannabis and cannabinoids and that there is a need to address these impediments so that researchers can draw more confident conclusions. The report makes four major recommendations:
- Address research gaps across the areas of basic and clinical research, policy, and public health and safety.
- Identify strategies to improve the quality of research on cannabis, including better research standards and benchmarks.
- Strengthen federal and state-based public health surveillance efforts to better track the effects of new policies.
- Address regulatory barriers to cannabis research.
Although a single report could not hope to address all the complexities of cannabis, cannabinoids, and their health effects, NASEM is to be commended for tackling a massive and often contradictory literature and for making a strong case for the need for further research. We will have more confident conclusions about this drug's benefits and its harms only when it is easier for qualified researchers across the country to do high-quality research.