Concerns about whether over-the-counter (OTC) allergy medications might affect brain development primarily focus on the types of antihistamines they contain and their ability to cross the blood-brain barrier. OTC allergy medications are commonly used to relieve symptoms such as runny nose, sneezing, and itchy eyes, but their impact on the brain, especially in children, has been a topic of discussion.
There are two main categories of antihistamines used in OTC allergy medications: first-generation and second-generation (and newer) antihistamines. First-generation antihistamines, such as diphenhydramine (commonly found in Benadryl), are known to cross the blood-brain barrier. This means they can enter the brain and cause sedation, drowsiness, and other central nervous system effects. Because these drugs block histamine receptors in the brain, they can interfere with normal brain functions like alertness, cognition, and memory. Histamine in the brain plays important roles in regulating the sleep-wake cycle, cognitive processes, and other neurophysiological functions. Therefore, blocking histamine receptors with first-generation antihistamines can potentially disrupt these processes.
In children, whose brains are still developing, there is concern that repeated or prolonged use of first-generation antihistamines might affect brain development or cognitive function. The anticholinergic effects of these drugs—meaning they block acetylcholine, a neurotransmitter important for learning and memory—raise additional worries. Anticholinergic medications have been linked in some studies to an increased risk of cognitive decline and dementia in older adults, and while direct evidence in children is limited, the potential for negative effects on developing brains is a reason for caution.
On the other hand, second-generation antihistamines, such as cetirizine (Zyrtec), loratadine (Claritin), and fexofenadine (Allegra), are designed to be more selective and less likely to cross into the brain. These medications provide allergy relief without causing significant sedation or drowsiness because they do not readily enter the central nervous system. For example, fexofenadine is known for its “0% brain interference,” meaning it does not cause drowsiness or impair concentration, which is particularly important for children who need to stay alert during school or play. Because these newer antihistamines have minimal effects on brain histamine receptors, the
