Why Cannabis Health Warnings Are Necessary: Americans Deserve More

why cannabis health warnings are necessary

The growing accessibility and legalization of marijuana/THC in the United States make it crucial to address public health concerns associated with its use. To ensure the well-being of Americans and enable informed decisions, the Food and Drug Administration (FDA) should require warning labels on federally illegal marijuana products both where it is legalized by states and where marijuana/THC is still illegal at the state level and federal level. There is a compelling case for implementing warning labels on federally illegal cannabis products to protect public health.

FDA Warnings and Information Requirements

Marinol® (THC) has been evaluated by the FDA; the medical risks associated with its use have been identified by the FDA. The public is warned through package inserts of the health risks of THC when taking Marinol (THC); this occurs in all states regardless of whether marijuana is legal or illegal in the state and even though the drug is illegal at the federal level. In addition, the FDA has also established warnings on the legal product tobacco, as it is a delivery mechanism for the drug nicotine. The American public should similarly be made aware of marijuana/THC health warnings, first and foremost the increased risk for psychosis.

Applying the Bradford Hill Criteria: Weighing the Evidence

Bradford Hill criteria comparing cannabis and tobacco

In evaluating the need for warning labels on marijuana products, we can turn to the Bradford Hill criteria—a set of guidelines used to establish causal relationships between exposures and outcomes. Applying these criteria to marijuana/THC use reveals convincing evidence of its potential harms, especially for the risk of psychosis and eventual schizophrenia. The Bradford Hill criteria are the same criteria used to conclude that smoking causes lung cancer.

    1. Strength of Association: Numerous studies demonstrate a clear link between marijuana/THC use and adverse mental health outcomes, including the psychotic disorder schizophrenia.
    2. Consistency: A consistent body of research across diverse populations and settings consistently supports the connection between marijuana/THC use and developing both temporary and chronic psychosis.
    3. Specificity: Of all the drugs which are associated with psychotic breaks, marijuana/THC is most likely to result the chronic psychotic disorder schizophrenia.
    4. Temporality: Longitudinal studies have demonstrated that marijuana/THC use often precedes the development of psychosis, consistent with a causal relationship.
    5. Biological Gradient: Evidence suggests a dose-response relationship, with heavier and more frequent marijuana/THC use correlating with increased risks of psychosis.
    6. Plausibility: The impacts of marijuana/THC on specific receptors and neurochemical pathways in the brain are consistent with changes known to underlie psychosis.
    7. Coherence: The observed health risks align with our understanding of marijuana/THC’s pharmacology and physiological effects.
    8. Experimental Evidence: Administration of THC to subjects under double-blind, controlled clinical conditions elicits psychotic symptoms even in those lacking a family history of psychosis.
    9. Analogy: Other drugs which can trigger psychotic breaks perturb some of the same neurochemical pathways and in similar manner as THC. For a detailed discussion of applying the Bradford Hill criteria to the marijuana/THC psychosis connection, along with supporting references, please visit IASIC1.org.
Austin Bradford Hill
Sir Austin Bradford Hill [1], CC BY 4.0, via Wikimedia Commons

Bridging the Regulatory Gap

All other drugs, including tobacco products, are sold with product-specific warnings. Requiring warning labels on legal marijuana/THC products is a vital step in safeguarding public health. These labels would provide crucial information to individuals, enabling them to make informed decisions about marijuana/THC use. A recent study by Moran et al., 2022 demonstrated an increased incidence of psychosis in areas where cannabis is legalized, thus warning labels should specifically address the increased risks for people living in these locales.

Americans Deserve More

Science-based warning labels can empower healthcare professionals and individuals to make informed decisions about marijuana/THC consumption. Just as was done successfully for tobacco, cannabis warning labels can be a powerful tool for promoting public health and individual choice.

Selected References

  • Hill AB. The Environment and Disease: Association or Causation? Proc R Soc Med. 1965;58(5):295-300. PMID: 14283879.
  • National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Board on Population Health and Public Health Practice; Committee on the Health Effects of Marijuana: An Evidence Review and Research Agenda. The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research. Washington (DC): National Academies Press (US); 2017 Jan 12. PMID: 28182287
  • S. Food and Drug Administration. Requirements for the Content, Format, and Execution of Labeling for Tobacco Products. Code of Federal Regulations Title 21, Part 1143. Updated 2021.
  • Carsten Hjorthøj, Christine Merrild Posselt, Merete Nordentoft. Development Over Time of the Population-Attributable Risk Fraction for Cannabis Use Disorder in Schizophrenia in Denmark. JAMA Psychiatry. 2021;78(9):1013-1019. doi:10.1001/jamapsychiatry.2021.1471.
  • Di Forti, M., et al. (2019). The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): A multicentre case-control study. The Lancet Psychiatry, 6(5), 427-436.
  • Moore, T. H., et al. (2007). Cannabis use and risk of psychotic or affective mental health outcomes: A systematic review. The Lancet Psychiatry, 370(9584), 319-328.
  • Moran LV, Tsang ES, Ongur D, Hsu J, Choi MY. Geographical variation in hospitalization for psychosis associated with cannabis use and cannabis legalization in the United States: Submit to: Psychiatry Research. Psychiatry Res. 2022;308:114387.

By: Catherine Antley, MD