Insomnia
While insomnia is a common symptom of depression, antidepressants are effective for treating sleep problems whether or not they are associated with depression. While all antidepressants help regulate sleep, some antidepressants such as amitriptyline, doxepin, mirtazapine, and trazodone can have an immediate sedative effect, and are prescribed to treat insomnia. Amitriptyline and doxepin both have antihistaminergic, anticholinergic, and antiadrenergic properties, which contribute to both their therapeutic effects and side effect profiles, while mirtazapine's side effects are primarily antihistaminergic, and trazodone's side-effects are primarily antiadrenergic. Mirtazapine is known to decrease sleep latency (i.e., the time it takes to fall asleep), promoting sleep efficiency and increasing the total amount of sleeping time in people with both depression and insomnia.
Clinical neurochemistry
Dyssomnia is a class of sleep disorders which includes Primary insomnia, primary hypersomnia, narcolepsy, breathing-related sleep disorders, circadian rhythm sleep discorer, and other conditions. Primary insomnia is a disorder in which a patient has difficulty initiating and maintaining sleep. Behavior modification and a reduction in neurologically active substances such as caffeine and alcohol seem to be among the most promising treatments. Although the mechanism is unknown, brain plasticity and behavior modification are utilized to train patients to only go to bed when tired, associating the bed itself with a sleepy state.