Top 5 Takeaways

  1. Prevalence of Antihistamine-Related Overdoses: 14.7% of overdose deaths (13,574 cases) were antihistamine-positive, and 3.6% (3,345 cases) were antihistamine-involved during 2019-2020.
  2. Dominance of Diphenhydramine: The majority of these cases involved first-generation H1 antihistamines, predominantly diphenhydramine.
  3. Demographic Patterns: Antihistamine-related overdose deaths were more common in females, persons aged 35-44, and White, non-Hispanic individuals.
  4. Co-occurrence with Opioids: A significant portion of these deaths co-involved opioids, particularly illicitly manufactured fentanyls (IMFs).
  5. Limitations of the Study: The study had limitations due to non-standardized drug testing methods and might not fully represent the national scenario.

Original Article Author and Citation

Corresponding Author

Amanda T. Dinwiddie,

Suggested Citation

Dinwiddie AT, Tanz LJ, Bitting J. Notes from the Field: Antihistamine Positivity and Involvement in Drug Overdose Deaths — 44 Jurisdictions, United States, 2019–2020. MMWR Morb Mortal Wkly Rep 2022;71:1308–1310. DOI:


The CDC analyzed 2019-2020 data from the State Unintentional Drug Overdose Reporting System (SUDORS) in 43 states and the District of Columbia to assess antihistamine involvement in overdose deaths. The study focused on unintentional and undetermined intent overdose deaths with antihistamine positivity or involvement.


A death was classified as antihistamine-positive if any antihistamine was detected in postmortem toxicology or listed as a cause of death on the death certificate. Antihistamine-involved deaths were a subset where the drug class was listed as a cause of death.


The study revealed that antihistamines, especially diphenhydramine, are frequently involved in drug overdose deaths. These findings are significant considering the over-the-counter availability of diphenhydramine and its potential sedative effects, especially when combined with opioids.


This study highlights the need for continued surveillance to understand the role of drugs and their combinations in overdose deaths. It underscores the potential dangers of the unpredictable illicit drug supply and unintentional co-use of substances like antihistamines and opioids.


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