Cannabis: Current Evidence and Research Recommendations
Medical use of cannabis has been a topic of controversy.
The use of cannabis in medicine has stirred substantial controversy in recent years, mostly stemming from uncertainties concerning the health risks and benefits of cannabis and its derivatives.
The National Academies of Sciences, Engineering, and Medicine (NASEM) recently released a report titled “The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendation for Research,” heralded by the organization as “one of the most comprehensive studies of recent research on the health effects of recreational and therapeutic cannabis use… offer[ing] a rigorous review of relevant scientific research published since 1999.” The report was released as an effort to summarize relevant research and identify gaps in knowledge and barriers to research in the field.1 A copy of the full report is available for download.
Conclusions were presented and discussed during a meeting held at the Academies on January 12, 2017, gathering members of NASEM's Board on Population Health and Public Health Practice, which produced the report.
Members of the committee who worked on the report are expert in fields that include substance abuse, neurodevelopment, epidemiology, cardiovascular health, and oncology. In order to accurately determine the current state of evidence in cannabis research, a systematic review was initiated in which online medical research databases (including Medline, Embase, and the Cochrane Database of Systematic Reviews) were consulted. Among the initial 24,000 articles identified, 10,000 abstracts were considered. The committee favored recent reviews featuring high-quality research focused on at least 1 of the 11 health end points considered to be a priority by the committee, including therapeutic effects, cardiometabolic risk, mental health, respiratory disease, and substance abuse.
Evidence was weighed and categorized as conclusive, substantial, moderate, limited, or insufficient by the committee. In addition, biologic plausibility, harms and benefits of cannabis use, and identification of observational studies were all considered in the crafting of the nearly 100 conclusions outlined in the report regarding the therapeutic benefits and health concerns associated with cannabis use.
Below are some of the more noteworthy conclusions included in this report.
“Conclusive or substantial evidence” was found for therapeutic benefits of cannabis:
- As an antiemetic in adults with chemotherapy-induced nausea or vomiting (orally)
- As a pain reliever in adults with chronic pain
- As an antispasmodic agent in adults with multiple sclerosis-associated spasticity (orally, short-term)
Evidence was found for the efficacy of cannabis in the treatment of sleep disturbances resulting from a number of etiologies (moderate evidence) and improving symptoms from Tourette syndrome and post-traumatic stress disorder (PTSD) (limited evidence).
Conversely, insufficient evidence was gathered to rule out the effectiveness of cannabis in improving symptoms associated with dementia, glaucoma, and chronic pain-associated depression.
Inadequate evidence was available for the committee to assess the therapeutic potential of cannabis in all other conditions evaluated, which included cancer, irritable bowel syndrome, amyotrophic lateral sclerosis, epilepsy, and chorea.
- Lack of association between cannabis use and the incidence of lung, head, or neck cancers (moderate evidence)
- Association between frequent and chronic cannabis smoking and nonseminoma-type testicular germ cell tumors (limited evidence)
- Association between cannabis use and all other types of cancers examined could neither be established nor refuted
Statistical associations were found between:
- Long-term cannabis smoking and a worsening of respiratory symptoms and a higher frequency of episodes of chronic bronchitis (substantial evidence)
- Acute use of cannabis smoking and an improvement in airway dynamics (moderate evidence)
- Cannabis smoking and a higher forced vital capacity (moderate evidence)
- Cessation of cannabis smoking and improvement in respiratory symptoms (moderate evidence)
Injury and Death
- Increased risk of death from motor vehicle accident following cannabis use
- Risk of unintentional cannabis overdose injuries among children”
- Lack of “clear evidence” establishing a link between cannabis use and risk of heart attack, stroke, and diabetes
- Impaired learning, memory, and attention-related performance associated with recent cannabis use (in past 24 hours)
- Negative impact of adolescent cannabis use on academic performance, future income, social relationships
- Association between cannabis use (particularly frequent use) and the development of psychoses, including schizophrenia (substantial evidence)
- Lack of association between cannabis use and increased risk of depression, anxiety, and PTSD
- Worsening of bipolar disorder-associated symptoms and increase in thoughts of suicide with near-daily/heavy cannabis use
Barriers and Challenges to Cannabis Research
- Classification of cannabis as Schedule I substance
- Difficulty for researchers in accessing sufficient quality cannabis
- Limited diversity of funders for cannabis research
- Substandard research methodology
- Address gaps in knowledge regarding the effects of cannabis on health through funding from a wide variety of sources for clinical and observational research, research on health policy and economics, public health and safety research
- Establish a workshop to develop research standards and benchmarks to improve the quality of cannabis research
- “Fund and support improvements to federal public health surveillance systems and state-based public health surveillance efforts”
- Devise strategies to address regulatory barriers to cannabis research
Recommendations 2 to 4 call for action by state, national, and federal agencies that include the National Institutes of Health, the Centers for Disease Control and Prevention, and the US Department of Health and Human Services.
The report concludes “This is a pivotal time in the world of cannabis policy and research. Shifting public sentiment, conflicting and impeded scientific research, and legislative battles have fueled the debate about what, if any, harms or benefits can be attributed to the use of cannabis or its derivatives. This report provides a broad set of evidence-based research conclusions on the health effects of cannabis and cannabinoids and puts forth recommendations to help advance the research field and better inform public health decisions.”
- National Academies of Science, Engineering, and Medicine. The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendation for Research. Washington, DC: The National Academies Press. doi: 10.17226/24625. http://www.nationalacademies.org/hmd/Reports/2017/health-effects-of-cannabis-and-cannabinoids.aspx. Accessed January 27, 2017.