Which CNS medication is known for causing sedation as a side effect?

The choice of antihistamines is accurate because many first-generation antihistamines are known to have sedative effects as a common side effect. These medications, such as diphenhydramine, work by blocking the action of histamine at H1 receptors, which is a mechanism that can also inhibit acetylcholine activity in the central nervous system, leading to drowsiness and sedation. This sedative property makes these antihistamines useful not only for treating allergies but also for conditions like insomnia and motion sickness.

In contrast, other classes of medications listed typically do not have sedation as a primary side effect. For instance, while some antidepressants can have sedating effects (such as certain tricyclic antidepressants), many of the newer antidepressants are actually designed to be activating or neutral with regard to sedation. Stimulants are primarily prescribed to increase alertness and concentration, making sedation counterintuitive to their purpose. Antipsychotics can vary; some may have sedative properties, but this is not as universally representative of the entire class compared to first-generation antihistamines. Therefore, among the options provided, antihistamines stand out as the class most consistently linked with sedation.