Antihistamine Use May Lead to Delirium for Older Adults: Study

Elderly individuals who develop delirium from side effects of Benadryl or other antihistamine may be more likely to fall, resulting in severe injuries that could greatly impact their quality of life.

A new Canadian study suggests older people who take Benadryl face a much higher risk of suffering from delirium, which can increase their risk of falls, injuries, malnutrition and dehydration.

According to findings published in the Journal of the American Geriatrics Society on October 22, hospital patients prescribed first-generation antihistamines, like Benadryl, had more than a 40% increased risk of experiencing delirium in the hospital.

Antihistamines are medications that treat allergy symptoms by blocking the histamine released during an allergic reaction. They are also given to treat hives and anaphylaxis, which can be deadly. 

Antihistamine Side Effects

First-generation antihistamines cause drowsiness and can impair cognitive function because they cross the blood-brain barrier. They include brands like Benadryl, ZzzQuil, Dimetapp and Chlor-Trimeton and are one of the leading causes of medication-related injuries to older adults. Although they can be lifesaving, they are often prescribed inappropriately and can cause falls, confusion and other side effects.

A study published in 2022 by the U.S. Centers for Disease Control and Prevention (CDC) concluded 15% of drug overdose deaths are linked to Benadryl and other antihistamines. Opioids and other street drugs are commonly cut with medications like Benadryl.

An older study published in 2015 warned of similar outcomes as the new study, concluding Benadryl was linked to an increased risk of dementia and permanent cognitive impairment.

However, second-generation antihistamines have been shown to cause less drowsiness and are less likely to cross the blood brain barrier as easily.

Researchers from the University of Toronto analyzed more than 328,000 inpatient admissions involving 755 doctors across 17 Ontario hospitals between April 2015 and March 2022. Among patients aged 65 and older, over 11,500 admissions included a prescription for a first-generation antihistamine such as Benadryl.

Led by Dr. Alanna C. Bridgman, the team found that patients admitted to the hospital had an overall risk of delirium of 35%. However, when patients were treated by doctors who often prescribed Benadryl, their risk of delirium increased by 41%.

Every 1% increase in the use of first-generation antihistamines, like Benadryl, led to an 8% increased risk of delirium, researchers determined. Doctors with the highest rates of Benadryl prescriptions prescribed the drug more than 5% of the time. That compares to only 2% prescription rates by doctors who rely less on first-generation antihistamines.

“These findings suggest that inpatient first-generation antihistamines may be associated with an increased risk of delirium, and their prescribing should be approached carefully for older adults.”

— Dr. Alanna C. Bridgman, Association of Inpatient Prescribing of First-Generation Antihistamines With Delirium in Older Adults: A Cross-Sectional Study

According to researchers, the study highlights a need for improved awareness among hospitals and doctors that the side effects of antihistamines which sedate patients can be harmful, especially to older patients, warning that first-generation antihistamines should be used with caution.

Sign up for more health and legal news that could affect you or your family.