Doxepin
In 2016 the American College of Physicians advised that insomnia be treated first by treating comorbid conditions, then with cognitive behavioral therapy and behavioral changes, and then with drugs; doxepin was among those recommended for short-term help maintaining sleep, on the basis of weak evidence. The 2017 American Academy of Sleep Medicine recommendations focused on treatment with drugs were similar. A 2015 AHRQ review of treatments for insomnia had similar findings.
Somnology
Of particular interest are the benzodiazepine drugs which reduce insomnia by increasing the efficiency of GABA. GABA decreases the excitability of neurons by increasing the firing threshold. Benzodiazepine causes the GABA receptor to better bind to GABA, allowing the medication to induce sleep.