Some widely used anti-allergy medicines known as first-generation antihistamines may increase the risk of confusion and long-term cognitive problems in older adults, according to a new study published in the Journal of the American Geriatrics Society.
Dementia currently affects about 57.4 million people around the world, and this number is expected to rise to more than 152 million by 2050. Early signs of the condition include memory loss, difficulty speaking or finding words, confusion, and behavioural changes.
Researchers from the University of Toronto and Women’s College Hospital analysed data from 328,140 patients aged 65 and above who were admitted to 17 hospitals in Ontario, Canada, between 2015 and 2022. They specifically looked at the type of antihistamines prescribed by 755 attending physicians.
The findings showed that 34.8 per cent of these hospitalised patients developed delirium — a sudden state of confusion, disorientation, or reduced awareness of surroundings. Importantly, patients treated by doctors who frequently prescribed first-generation antihistamines had a 41 per cent higher chance of developing delirium compared to those whose doctors rarely used these medications.
Drugs like diphenhydramine fall under the first-generation antihistamine group. They are known to have strong sedative effects and can cross into the brain, affecting cognitive function. Although useful in treating allergic reactions such as hives and anaphylaxis, these medicines are sometimes misused for conditions like non-specific itching, where they are not necessary.
Delirium is a serious concern because it affects up to half of older hospital patients and is linked to complications such as longer hospital stays, increased mortality, and a higher risk of developing long-term memory problems, including dementia.
The researchers stressed that second-generation or non-sedating antihistamines, which are commonly available and effective, are much safer for older adults.
“We hope our study raises awareness among doctors that sedating antihistamines can be harmful in the elderly and should be prescribed with caution,” said lead author Dr Aaron M. Drucker.
Medical experts advise that older adults and caregivers should speak to healthcare providers before using first-generation antihistamines, especially when safer alternatives are available.
