Although people have used cannabis for its therapeutic for centuries, there has been little in the way of rigorous scientific study to show conclusive evidence of its medical benefits.
The National Academy of Sciences, Engineering and Medicine has released a comprehensive report called The Health Effects of Cannabis and Cannabinoids that acknowledges “conclusive or substantial evidence” exists for cannabis’ benefits for treating chronic pain, and sharply criticized federal barriers to marijuana research in the U.S. – in particular the classification of cannabis as a Schedule I prohibited substance under federal law. Researchers considered more than 10,000 scientific abstracts to reach nearly 100 conclusions, and the report also proposes ways to expand and improve the quality of cannabis research efforts.
“For years the landscape of marijuana use has been rapidly shifting as more and more states are legalizing cannabis for the treatment of medical conditions and recreational use,” said head researcher Marie McCormick. “This growing acceptance, accessibility, and use of cannabis and its derivatives have raised important public health concerns. Moreover, the lack of any aggregated knowledge of cannabis-related health effects has led to uncertainty about what, if any, are the harms or benefits from its use. We conducted an in-depth and broad review of the most recent research to establish firmly what the science says and to highlight areas that still need further examination.”
Here’s what they found:
One of the therapeutic uses of cannabis and cannabinoids is to treat chronic pain in adults. The committee found evidence to support that patients who were treated with cannabis or cannabinoids were more likely to experience a significant reduction in pain symptoms. For adults with multiple sclerosis-related muscle spasms, there was substantial evidence that short-term use of certain “oral cannabinoids” – man-made, cannabinoid-based medications that are orally ingested – improved their reported symptoms. Furthermore, in adults with chemotherapy-induced nausea and vomiting, there was conclusive evidence that certain oral cannabinoids were effective in preventing and treating those ailments.
Injury and Death
Evidence suggests that cannabis use prior to driving increases the risk of being involved in a motor vehicle accident. Furthermore, evidence suggests that in states where cannabis use is legal, there is increased risk of unintentional cannabis overdose injuries among children. In one study, ingestion was the most common route of unintentional pediatric exposure, accounting for 78 percent of all incidents. Another study reported that from 2000 to 2013, the annual rate of poison center calls related to cannabis exposures among children younger than 6 years of age was 2.82 times higher in states that had legalized medical cannabis prior to 2000 than in states where medical cannabis remained illegal as of 2013. The committee called for more research to determine whether and how cannabis use is associated with death or with occupational injury.
Regarding the link between marijuana and cancer, the committee found evidence that suggests smoking cannabis does not increase the risk for cancers often associated with tobacco use – such as lung and head and neck cancers. The committee also found limited evidence that cannabis use is associated with one sub-type of testicular cancer and insufficient evidence that cannabis use by a mother or father during pregnancy leads to a greater risk of cancers in the child.
Heart Attack, Stroke, and Diabetes
The committee said that more research is needed to determine whether and how cannabis use is associated with heart attack, stroke, and diabetes. However, some evidence suggests that cannabis smoking may trigger a heart attack.
The evidence reviewed by the committee suggests that smoking cannabis on a regular basis is associated with more frequent chronic bronchitis episodes and worse respiratory symptoms, such as chronic cough and phlegm production, but quitting cannabis smoking is likely to reduce these conditions. The committee stated that it is unclear whether cannabis use is associated with certain respiratory diseases, including chronic obstructive pulmonary disease, asthma, or worsened lung function.
There is a lack of data on the effects of cannabis or cannabinoid-based therapeutics on the human immune system, as well as insufficient data to draw overarching conclusions concerning the effects of cannabis smoke or cannabinoids on immune competence, the committee stated. There is also insufficient evidence to support or refute a statistical association between cannabis or cannabinoid use and adverse effects on immune status in individuals with HIV. Nevertheless, limited evidence suggests that regular exposure to cannabis smoke may have anti-inflammatory activity.
The evidence reviewed by the committee suggests that cannabis use is likely to increase the risk of developing schizophrenia, other psychoses, and social anxiety disorders, and to a lesser extent depression. Alternatively, in individuals with schizophrenia and other psychoses, a history of cannabis use may be linked to better performance on learning and memory tasks. Heavy cannabis users are more likely to report thoughts of suicide than non-users, and in individuals with bipolar disorder, near-daily cannabis users show increased symptoms of the disorder than non-users.
Cannabis Use and the Abuse of Other Substances
The committee found limited evidence that cannabis use increases the rate of initiating other drug use, primarily the use of tobacco. However, the committee found moderate evidence to suggest that there is a link between cannabis use and the development of substance dependence and/or a substance abuse disorder for substances including alcohol, tobacco, and other illicit drugs.
The committee found that learning, memory, and attention are impaired after immediate cannabis use. Limited evidence suggests that there are impairments in cognitive domains of learning, memory, and attention in individuals who have stopped smoking cannabis. In addition, there is limited evidence to suggest that cannabis use is related to impairments in subsequent academic achievement and education as well as social relationships and social roles. Adolescence and young adulthood are when most youth begin to experiment with substances of abuse, including cannabis, and it is during these periods that the neural layers that underlie the development of cognition are most active. The committee also found limited evidence of an association between cannabis use and increased rates of unemployment and low income.
Prenatal, Perinatal, and Neonatal Exposure
Smoking cannabis during pregnancy is linked to lower birth weight in the offspring, some evidence suggests. However, the relationship with other pregnancy and childhood outcomes is unclear.
Challenges and Barriers in Conducting Cannabis Research
In addition to recommending more research on the beneficial and harmful effects of cannabis and cannabinoid use, the committee emphasized several challenges and barriers in conducting such research. For instance, specific regulatory barriers, including the classification of cannabis as a Schedule I substance, impede the advancement of research. Researchers also often find it difficult to gain access to the quantity, quality, and type of cannabis product necessary to address specific research questions. The committee said a diverse network of funders is needed to support cannabis and cannabinoid research.
The study was sponsored by Alaska Mental Health Trust Authority, Arizona Department of Health Services, California Department of Public Health, Centers for Disease Control and Prevention (CDC), CDC Foundation, U.S. Food and Drug Administration, Mat-Su Health Foundation, National Highway Traffic Safety Administration, National Institutes of Health National Cancer Institute, National Institutes of Health National Institute on Drug Abuse, Oregon Health Authority, Robert W. Woodruff Foundation, The Colorado Health Foundation, Truth Initiative, and Washington State Department of Health. The National Academies of Sciences, Engineering, and Medicine are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology, and medicine. The National Academies operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln. For more information, visit http://national-academies.org.