South Dakota Medication Aide Practice Test

The most frequent side effect experienced with antihistamines is sedation. Antihistamines are primarily used to treat allergic reactions by blocking histamine, a substance in the body that causes allergic symptoms. However, many first-generation antihistamines, such as diphenhydramine and chlorpheniramine, are known for their sedative properties. This sedative effect occurs because these medications can cross the blood-brain barrier and inhibit the action of histamine in the central nervous system, which normally promotes wakefulness.

Sedation can manifest as drowsiness, fatigue, or decreased alertness, making it a common and significant consideration for individuals taking these medications, especially when they need to drive or operate machinery. While other side effects such as constipation, headaches, and dizziness can occur, they are less frequently reported compared to sedation. Understanding this side effect is vital for safe medication management and for informing patients about what to expect when using antihistamines.