Which of the following agents is considered for pharmacotherapy in adults with acute insomnia?

Doxepin is a tricyclic antidepressant that has been specifically studied and found to be effective for the treatment of acute insomnia. It works by blocking histamine H1 receptors, which contributes to its sedative effects. Its low dose form, specifically designed for sleep maintenance, has been shown to improve sleep quality and increase total sleep time without causing significant next-day residual effects, making it a suitable choice in pharmacotherapy for acute insomnia.

Melatonin, while often used for sleep disorders, primarily helps with the regulation of circadian rhythms and may not be as effective in the immediate management of acute insomnia. Valerian root and chamomile are herbal remedies that lack the clinical evidence and regulatory approval typically associated with pharmacotherapy options. While they may have some calming effects, they are not considered first-line treatments for acute insomnia in adults like doxepin is.