Several antidepressants are widely prescribed for sleep problems, even though only one, low-dose doxepin, is actually FDA-approved for insomnia. The rest are used off-label at doses well below what’s needed for treating depression. Trazodone is the most commonly prescribed, followed by mirtazapine and older tricyclic antidepressants like amitriptyline. Each works differently, and the tradeoffs in side effects vary enough that the choice matters.
Why Some Antidepressants Make You Sleepy
Not all antidepressants promote sleep. SSRIs like sertraline and fluoxetine can actually worsen insomnia and increase restless legs or teeth grinding during sleep. The antidepressants that help with sleep share a common trait: they block histamine receptors in the brain, the same receptors targeted by over-the-counter sleep aids like diphenhydramine. Some also block serotonin receptors and adrenaline-related receptors, which together promote deeper relaxation and drowsiness.
An important pattern runs through most of these medications: they tend to be more sedating at lower doses. That sounds counterintuitive, but at low doses, the histamine-blocking effect dominates. At higher doses, other effects kick in that can be more activating. This is why doctors often prescribe these drugs at a fraction of their antidepressant dose when the goal is purely better sleep.
Trazodone
Trazodone is the single most commonly prescribed medication for insomnia in the United States, and it’s used at doses far below its antidepressant range. For sleep, the typical dose is 25 to 100 mg at bedtime. For depression, doses range from 150 to 600 mg. At those low sleep-focused doses, trazodone blocks serotonin, histamine, and adrenaline receptors simultaneously, producing sedation without much antidepressant effect.
Clinical trials pooling data from 370 participants found that trazodone produced a moderate improvement in subjective sleep quality compared to placebo. That said, the American Academy of Sleep Medicine’s 2017 guidelines actually recommend against using trazodone for insomnia, citing limited evidence (a weak recommendation, not a strong one). The concern isn’t that it doesn’t work for many people, but that the clinical trial data supporting it is thinner than for other options. Morning grogginess, dry mouth, and increased thirst are the most commonly reported side effects.
Doxepin (the Only FDA-Approved Option)
Low-dose doxepin is the only antidepressant with formal FDA approval for treating insomnia, granted in 2010. It’s approved at just 3 mg and 6 mg for both adults and elderly patients with chronic insomnia. For comparison, its antidepressant dose ranges from 75 to 150 mg. At these very low doses, doxepin works almost exclusively by blocking histamine receptors.
Clinical trials confirmed that doxepin at 3 mg and 6 mg improves how quickly people fall asleep, how long they stay asleep, and their overall sleep quality. The American Academy of Sleep Medicine gives it a weak recommendation specifically for sleep maintenance insomnia, meaning difficulty staying asleep through the night rather than trouble falling asleep initially. Because the dose is so low, side effects tend to be mild compared to other options in this category.
Mirtazapine
Mirtazapine is FDA-approved as an antidepressant at 15 to 45 mg per day, but doctors frequently prescribe it off-label at 7.5 to 15 mg at bedtime primarily for its sleep-promoting effects. Like trazodone, its sedation is strongest at lower doses because histamine blockade dominates before other receptor effects emerge.
Mirtazapine can be particularly useful when insomnia coexists with depression, poor appetite, or significant weight loss, because it reliably increases appetite. That same trait is a drawback for many people: in one long-term comparison study, 13% of patients on mirtazapine experienced measurable weight gain. Daytime drowsiness is also a significant concern. Research presented at a major sleep conference found that even at low doses of 7.5 to 15 mg, roughly 54% of patients reported troublesome daytime drowsiness, often described as feeling hungover.
Tricyclic Antidepressants
Older tricyclic antidepressants, particularly amitriptyline, have been used for decades to treat insomnia, especially in patients who also have chronic pain. Low doses of 10 to 25 mg at bedtime are common practice, particularly in the UK. A Cochrane review pooling data from four studies with 510 participants found that tricyclics improved sleep efficiency by about 6 percentage points and increased total sleep time by roughly 23 minutes per night compared to placebo.
Tricyclics carry more baggage than newer options. They have stronger anticholinergic effects, which can cause dry mouth, constipation, blurred vision, and urinary retention. They’re dangerous in overdose, which is a meaningful concern when prescribing to people with depression. In a long-term study, 22% of patients on amitriptyline experienced weight gain. These medications also strongly suppress REM sleep while increasing deep slow-wave sleep, which changes the overall structure of your sleep in ways that may or may not be desirable long-term.
How These Drugs Affect Sleep Stages
Different antidepressants reshape your sleep architecture in distinct ways. Tricyclic antidepressants and MAOIs strongly suppress REM sleep (the stage associated with dreaming) while significantly boosting slow-wave deep sleep. SSRIs and SNRIs also reduce REM sleep, though less dramatically. Trazodone suppresses REM sleep as well, though its effect on deep sleep is generally considered more favorable than SSRIs.
This matters because REM sleep plays a role in emotional processing, memory consolidation, and learning. Long-term suppression of REM sleep is not fully understood, but it’s one reason sleep specialists often prefer behavioral treatments like cognitive behavioral therapy for insomnia (CBT-I) as a first-line approach. These medications change not just how much you sleep, but the kind of sleep you get.
Risks for Older Adults
Sedating antidepressants pose particular risks for people over 65. The sedation that helps with sleep also impairs reaction time during the night and into the next morning, increasing the risk of falls. Tricyclics and trazodone are potent histamine blockers that can cause significant daytime drowsiness. Anticholinergic effects from tricyclics further raise fall risk by causing low blood pressure when standing, blurred vision, and impaired cognitive function.
Mirtazapine, often assumed to be gentler, also requires caution in older adults. A large observational study found that mirtazapine was associated with a higher rate of adverse events than other antidepressants in this age group. Low-dose doxepin (3 or 6 mg) is the only option in this class specifically approved for use in elderly patients with insomnia, and its minimal dosing helps limit these concerns. For older adults with fall risk, behavioral therapy for insomnia is generally considered the safest first step.
What Sleep Specialists Prefer
Despite how widely these medications are prescribed, no major sleep organization enthusiastically endorses antidepressants as a go-to insomnia treatment. The American Academy of Sleep Medicine gives only a weak recommendation to doxepin and actively recommends against trazodone, though that recommendation is also weak rather than strong. A Cochrane review concluded bluntly that antidepressant use for insomnia is widespread, but none is licensed for insomnia (outside of low-dose doxepin), and the evidence for their efficacy remains unclear.
This doesn’t mean these medications are useless. Millions of people sleep better on low-dose trazodone or mirtazapine, and for someone dealing with both depression and insomnia, a sedating antidepressant can address two problems at once. But the evidence base is thinner than most people assume, and the side effect profiles, from next-day grogginess to weight gain to altered sleep architecture, are real tradeoffs worth understanding before starting one.