Professor, Epidemiology and Systems Pharmacology and Translational Therapeutics
University of Pennsylvania Perelman School of Medicine, Philadelphia
Committee on the Health Effects of Marijuana: An Evidence Review and Research Agenda
Board on Population Health and Public Health Practice
Health and Medicine Division
The National Academies of Sciences, Engineering, and Medicine
Caucus on International Narcotics Control
October 23, 2019
Good afternoon. My name is Sean Hennessy and I am a pharmacist‐epidemiologist and faculty member at the University of Pennsylvania. I was a member of the 16‐person committee that wrote the report entitled The Health Effects of Cannabis and Cannabinoids1 that the National Academies of Science, Engineering and Medicine released in January 2017.
More than 150 years ago, the National Academy of Sciences was created through a congressional charter signed by Abraham Lincoln to serve as an independent, authoritative body outside the government that could advise the nation on matters pertaining to science and technology. It later expanded to include engineering and medicine. Every year, approximately 6,000 National Academies members and volunteers serve pro bono on consensus study committees or convening activities. The National Academies’ consensus study process is considered the gold standard of independent, nonpartisan, evidence‐based advice.
Our committee conducted a comprehensive review and synthesis of the existing evidence regarding the potential health effects—both therapeutic and harmful—of cannabis and cannabis‐derived products. Our 487‐page report lists nearly 100 different conclusions about these effects. It also lists four recommendations to address research gaps, improve research quality, improve surveillance capacity, and address research barriers. I’d like to briefly summarize what our committee found and recommended. I have attached a copy of the report’s highlights
for your reference.
For each potentially therapeutic or harmful health effect that we examined, our committee classified the evidence as either conclusive, substantial, moderate, limited, or as no or insufficient evidence.
Potential Therapeutic Effects
We found conclusive evidence that orally administered tetrahydrocannabinol (THC) is effective in treating chemotherapy‐induced nausea and vomiting. Synthetic THC (dronabinol) and a synthetic analogue of THC (nabilone) are both FDA‐approved for this use.
We found substantial evidence that some cannabis products are effective for the treatment of chronic pain in adults. Of the trials examined, 13 studied a product called nabiximols (an oral‐mucosal cannabis extract containing equal amounts of THC and CBD), 7 studied cannabis flower that was either smoked or vaped, 5 studied orally administered synthetic THC, and 3 studied THC oramucosal spray.
We found substantial evidence that orally administered cannabinoids (nabiximols and nabilone) can improve patient‐reported symptoms of muscle spasticity in persons with multiple sclerosis.
We found moderate evidence that cannabis‐derived products, primarily nabiximols, can improve short-term sleep in persons with sleep disturbance associated with obstructive sleep apnea, fibromyalgia, chronic pain, and multiple sclerosis.
We found only limited evidence that cannabis and oral cannabinoids can increase appetite and reduce weight loss associated with HIV/AIDS; that that oral cannabinoids can improve clinician‐measured muscle spasticity in persons with multiple sclerosis; that oral THC can improve symptoms of Tourette syndrome; that oral CBD can improve anxiety symptoms in individuals with social anxiety disorders; and that nabilone can improve symptoms of posttraumatic stress disorder.
There were many conditions for which we found no or insufficient evidence that cannabis or cannabis-derived products were effective, including cancers, irritable bowel syndrome, and Parkinson disease.
After we issued our report, the results of clinical trials were made available that served as the basis for the approval by the US Food and Drug Administration of concentrated CBD oil (Epidiolex®) for use as part of a multi‐drug treatment for two rare and severe forms of epilepsy.2 For reasons of transparency, I note that I served as a consultant for Greenwich Biosciences, Inc. in 2018 and received consulting fees that were less than the $5000 threshold for a “significant financial interest” set by the US Department of Health and Human Services.
Potential Harmful Health Effects
We found substantial evidence of a statistical association between recent cannabis use and an increased risk of motor vehicle crashes.
We found substantial evidence of a statistical association between maternal cannabis smoking and lower birth weight of the offspring.
We found substantial evidence of a statistical association between long‐term cannabis smoking and worse respiratory symptoms including cough, increased sputum production, wheeze, and more frequent chronic bronchitis episodes.
We found substantial evidence that initiating cannabis use at an earlier age is a risk factor for the development of problem cannabis use.
We found substantial evidence of a statistical association between cannabis use and the development of schizophrenia or other psychoses, with the highest risk among the most frequent users. However, there is reason to question about the directionality of this association.
We found moderate evidence of a statistical association between acute cannabis use and impairment in learning, memory, and attention.
We found moderate evidence of a statistical association between regular cannabis use and increased symptoms of mania and hypomania in individuals diagnosed with bipolar disorders.
We found moderate evidence of a statistical association between cannabis use and a small increased risk for the development of depressive disorders.
We found moderate evidence of a statistical association between cannabis use and increased incidence of suicidal ideation, suicide attempts, and completed suicide.
We found moderate evidence of a statistical association between regular cannabis use and increased incidence of social anxiety disorder.
We found moderate evidence that during adolescence the frequency of cannabis use, oppositional behaviors, a younger age of first alcohol use, nicotine use, parental substance use, poor school performance, antisocial behaviors, and childhood sexual abuse are risk factors for the development of problem cannabis use.
We found moderate evidence of a statistical association between cannabis use and the development of substance dependence and/or a substance abuse disorder for substances, including alcohol, tobacco, and other illicit drugs.
We found moderate evidence of a statistical association between cannabis use and an increased risk of overdose injuries among pediatric populations in U.S. states where cannabis is legal according to state law.
Barriers to Research on the Effects of Cannabis and Cannabis‐derived Products
Our committee identified four challenges to conducting research on the health effects of cannabis:
- There are specific regulatory barriers, including the classification of cannabis as a Schedule I substance, that impede the advancement of cannabis and cannabinoid research.
- It is often difficult for researchers to gain access to the quantity, quality, and type of cannabis product necessary to address specific research questions on the health effects of cannabis use.
- A diverse network of funders is needed to support cannabis and cannabinoid research that explores the beneficial and harmful health effects of cannabis use.
- To develop conclusive evidence for the effects of cannabis use on short‐ and long‐term health outcomes, improvements and standardization in research methods are needed.
Our committee made the following four recommendations:
- To develop a comprehensive evidence base on the short‐ and long‐term health effects of cannabis use (both beneficial and harmful effects), public agencies, philanthropic and professional organizations, private companies, and clinical and public health research groups should provide funding and support for a national cannabis research agenda that addresses key gaps in the evidence base.
- To promote the development of conclusive evidence on the short‐ and long‐term health effects of cannabis use (both beneficial and harmful effects), agencies of the U.S. Department of Health and Human Services should jointly fund a workshop to develop a set of research standards and benchmarks to guide and ensure the production of high‐quality cannabis research.
- To ensure that sufficient data are available to inform research on the short‐ and long‐term health effects of cannabis use, the federal, state, and local health authorities should fund and support improvements to federal public health surveillance systems and state‐based public health surveillance efforts.
- The Centers for Disease Control and Prevention, National Institutes of Health, U.S. Food and Drug Administration, industry groups, and nongovernmental organizations should fund the convening of a committee of experts tasked to produce an objective and evidence‐based report that fully characterizes the impacts of regulatory barriers to cannabis research and that proposes strategies for supporting development of the resources and infrastructure necessary to conduct a comprehensive cannabis research agenda.
Thank you for your attention and the opportunity to discuss these issues. I look forward to answering your questions.