Which medication is least likely to cause cognitive impairment in an elderly patient with insomnia?

Ramelteon is the least likely medication to cause cognitive impairment in an elderly patient with insomnia due to its unique pharmacological profile. Unlike many other sleep aids, ramelteon is a selective melatonin receptor agonist, meaning it mimics the action of melatonin, a hormone that regulates sleep-wake cycles without exerting significant sedative effects or depression of the central nervous system.

In contrast, diphenhydramine, a first-generation antihistamine, is known to have anticholinergic properties, which can contribute to cognitive decline, particularly in elderly patients. Zolpidem and alprazolam are both classified as CNS depressants—the former is a sedative-hypnotic, and the latter is a benzodiazepine. These medications can impair cognitive function by causing sedation, confusion, and memory problems, especially in older individuals who may be more sensitive to the effects of such drugs.

Ramelteon's selective action on melatonin receptors allows it to promote sleep without the same risks of cognitive impairment associated with the other options. This makes it a more suitable choice for elderly patients experiencing insomnia, as it helps manage sleep issues without jeopardizing cognitive function.