THURSDAY, Oct. 23, 2025 (HealthDay News) -- Older adults admitted to physicians with higher prescribing of first-generation antihistamines are more likely to experience delirium in the hospital, according to a study published online Oct. 22 in the Journal of the American Geriatrics Society.Alanna C. Bridgman, M.D., from the University of Toronto, and colleagues estimated the association between inpatient physician prescribing of first-generation antihistamines and delirium among older general medicine inpatients in a cross-sectional study. The study used inpatient admissions between April 1, 2015, and March 31, 2022, across 17 hospitals in Ontario among adults aged 65 years and older from the GEMINI database.The researchers found that 3.5 percent of 328,140 inpatient admissions to 755 physicians included a first-generation antihistamine prescription. A first-generation antihistamine was prescribed during 2.1 and 5.4 percent of admissions by physicians in the lowest- and highest-prescribing quartiles, respectively. Delirium occurred in 32.3 and 36.6 percent of admissions to the lowest- and highest-prescribing quartiles of physicians, respectively. Each 1 percent absolute increase in first-generation antihistamine prescribing was associated with 8 percent increased odds of delirium in adjusted analyses (adjusted odds ratio, 1.08). The odds of delirium were increased 41 percent for patients admitted to physicians in the highest versus lowest quartiles (adjusted odds ratio, 1.41)."We hope our study raises awareness among hospitalists that sedating antihistamines can be harmful, and should be prescribed with caution," co-author Aaron M. Drucker, M.D., also from the University of Toronto, said in a statement.Abstract/Full Text.Sign up for our weekly HealthDay newsletter