ITCHY eyes, constant sneezing, a runny nose… all signs hay fever season is well and truly here.
Yep, that joyous time of the year when one in four Brits dreads the smell of freshly-cut grass and ends up spluttering, and non-stop if they dare head outside.
The tends to hit between March and September, when the from grass and trees is at its highest, and sees sufferers taking regularly to reduce .
However, some research suggests that antihistamines can impact brain .
When asked last month if we should worry about dementia risk from antihistamines, Harvard doctor Anthony L. Komaroff, MD said he would “think twice about taking antihistamines and other medicines with anticholinergic effects”;.
“I weigh the symptom relief they give me against the possibility that they may slightly increase my risk of developing dementia,”; he added.
However, Komaroff acknowledged that there is “conflicting evidence”; and that all existing studies on the topic are “inherently flawed”;.
So how worried should we be about taking these everyday , when many of us are used to popping them throughout spring and summer? We reveal all.
What are antihistamines used for?
“ANTIHISTAMINES are used to treat allergies, such as hay fever, conjunctivitis, hives and insect stings,”; explains Dr Deborah Lee, from Dr Fox Online Pharmacy.
“They are also used to treat motion sickness and as a short-term treatment for insomnia.”;
You can take them as drops, tablets, sprays and more, and they’re available on prescription as well as over the counter in pharmacies and supermarkets.
Most of us have some Piriton in the cupboard somewhere, they’re that common.
“Antihistamines are used by millions of patients each year for allergic conditions,”; says Dr Robin Gore, president of the British Society for Allergy & Clinical Immunology (BSACI).
“Many patients with mild allergic diseases only take doses intermittently.
“For patients with more severe allergic disease, clear guidelines exist to help doctors add in other, non-antihistamine therapies to control disease so that allergy sufferers do not simply increase antihistamine doses but seek more effective alternatives.”;
What types of antihistamines are there?
THERE are two key groups of antihistamines according to the NHS: drowsy and non-drowsy.
“First generation antihistamines (FGAs) such as diphenhydramine (Benadryl), chlorphenamine (Piriton) and promethazine (Phenergan) easily cross the blood brain barrier and cause sedation,”; says Dr Lee.
“FGAs can have anticholinergic side effects, including dry mouth, dry eyes, dilated pupils and a fast heart rate.”;
She adds: “The newer, second-generation antihistamines (SGAs) such as cetirizine (Zyrtec), loratadine (Claritin) and fexofenadine (Allegra) do not enter the brain so easily.
“They are regarded as non-drowsy and have a longer duration of action.”;
Dr Gore says: “SGAs include cetirizine, loratadine, desloratadine and fexofenadine and are now widely recommended for patients with allergic conditions.
“They are considered much safer than FGAs and are far less likely to have any sedative effects.”;
How have antihistamines been linked with brain health?
DRUGS with anticholinergic side effects have been found to have a possible link with – they may increase brain inflammation or block certain important neurotransmitters – but the research is not conclusive.
“Several research studies have shown an increase in dementia in those who have taken anticholinergic drugs, which include antihistamines,”; says Dr Lee.
“However, these are either observational or case-controlled studies – research methodology where something has been observed to happen to a specific group of people – but causation cannot be proven.”;
Dr Gore adds: “FGAs are known to have extra biological effects in addition to their ‘anti-allergy, antihistamine’ purpose.
“These extra effects (called ‘anticholinergic’) are shared with some other medications used for other conditions and have given cause for concern in respect of the development of cognitive impairment and dementia when used by older adults, as reported in other studies.”;
Hay fever symptoms can be extremely unpleasant and significantly lower your quality of life
Dr Deborah Lee
He adds: “In young people, research has highlighted the effects of FGAs on concentration: young people on sedating antihistamines with seasonal rhinitis may suffer lower examination grades.
“There is no research in young people to show any long-term irreversible effects of antihistamines on memory.”;
However, FGAs are “no longer routinely recommended for use for allergic diseases”;, notes Dr Gore.
One 2024 article, by Chun-Hung Su and co, from the Chung Shan Medical University in Taichung, Taiwan, reported on the effects of taking FGAs and SGAs on the risk of dementia.
The researchers looked at patients who were aged over 50 and had .
“The authors report a link between the use of antihistamines and the development of dementia,”; says Dr Gore.
“The link they report is strongest for older FGAs than with the newer SGAs.
“They report a dose response: taking higher doses for longer seems to make the link look stronger.”;
Because the paper is retrospectively reported, Dr Gore says: “This means that patients are studied ‘in the past’ and this makes it difficult to eliminate biases that may affect the accuracy of the results.
“Other large studies using a range of different methods have investigated many different types of medication and the risk of dementia.
“The results from these studies differ widely.
“Dr Su and colleagues are right to point out that further studies are needed to more accurately determine any effect of SGAs on the development of dementia.”;
How worried should people be about taking any type of antihistamine?
“IN general people should not be overly worried about this,”; says Dr Lee.
“The concern is about long term, frequent – not occasional – use of first generation antihistamines.
“The newer second generation antihistamines are more commonly used these days, and they have no demonstrable anticholinergic effects, so an association with dementia risk is less likely.”;
She adds: “Hay fever symptoms can be extremely unpleasant and significantly lower your quality of life.
“For the majority of sufferers, taking a second generation antihistamine for a few months of the year is more likely to confer benefit than harm.”;
Dr Gore adds: “Any risk should be put into context: the size of the risk from the use of moderate doses of SGAs reported in [Dr Su’s] study is equivalent to the risk of dementia from simply being female.
“Females have a slightly higher risk of dementia than males.
“This risk is dwarfed by the increase in dementia risk that occurs with simply being older: one in five to one in six people in the UK over the age of 80 will have a dementia condition and many other risk factors can contribute to this risk, aside from medication.”;
Should people stop taking antihistamines?
DON’T suddenly bin your .
Dr Gore says: “Based on current evidence, people with allergic disease who need to use second generation antihistamine tablets (SGAs) such as loratadine, fexofenadine, cetirizine, desloratadine, or the nasal spray azelastine (often given in a combination dose with a nasal steroid) should not stop taking them.
“Allergy sufferers with poorly controlled rhinitis and who are only using antihistamine tablets – especially as we move into spring and summer, peak times for tree pollen allergic rhinitis and grass pollen hay fever – should speak to their pharmacist about other medications to improve symptoms.”;
He recommends adding a nasal steroid spray to your routine, which doesn’t require a prescription as it “is much better at improving symptoms than simply increasing the use of antihistamine tablets”;.
Dr Gore says: “People on any long term antihistamine on repeat prescription should have this medication reviewed at their next annual medication review, to ensure that they are on an appropriate medication.
“Patients using FGAs should get advice from their GP or pharmacist if they are at all concerned.
“There are alternatives available and GPs and pharmacists can help.”;
