What side effect is commonly associated with antihistamines due to their sedative properties?

Antihistamines are known for their sedative properties, which are primarily due to their ability to cross the blood-brain barrier and inhibit the action of histamine, a neurotransmitter that promotes wakefulness. As a result, one of the most commonly reported side effects of antihistamines is drowsiness. This sedative effect can be particularly pronounced in first-generation antihistamines, which are more likely to cause central nervous system effects because they are less selective in their action and can affect other neurotransmitter systems, leading to a calming or sedative effect. This side effect is often why these medications are used not only for allergic reactions but also for their sleep-inducing properties. In contrast, other side effects like increased heart rate, nausea, and dry mouth are less directly related to the sedative properties of antihistamines and may result from different mechanisms or the specific type of antihistamine used.