Mirtazapine for Sleep: What the Evidence Shows

Mirtazapine is one of the medications people end up taking for poor sleep. It is often prescribed after someone mentions trouble sleeping to their doctor, particularly alongside a persistent low mood. The drug is known for being sedating — and although it is approved for major depressive disorder, it is sometimes prescribed off-label for insomnia. That means it was not approved on the strength of studies showing it treats insomnia.

What it is approved for

The FDA label is straightforward. Mirtazapine, sold under the brand name Remeron, is indicated for the treatment of major depressive disorder in adults.1 It belongs to a class called tetracyclic antidepressants, and is understood to work by blocking particular serotonin and histamine receptors.

Because of that effect on histamine receptors, mirtazapine frequently causes drowsiness — which is why it is sometimes prescribed off-label for people who cannot sleep. Off-label prescribing is legal, common and often medically reasonable.

It also means the dose and the duration are left to the prescriber's judgment rather than set by the label. Prescribed for insomnia, mirtazapine is typically given at a lower dose than for depression.

How common is drowsiness with mirtazapine?

The label reports the six-week placebo-controlled trials. Somnolence was reported in 54% of patients treated with mirtazapine, against 18% on placebo.1

That is an unusually wide gap. For most drugs, sedation is a side effect to be managed. For mirtazapine it is strong enough to have become a reason to prescribe it.

The label's starting dose is 15 mg once daily, usually in the evening before bed, with a maximum of 45 mg once daily.1 For sleep, lower doses are typically used.

What the evidence shows

Two 2025 trials tested it directly for insomnia.

In MIRAGE, 60 adults aged 65 and over with chronic insomnia took either 7.5 mg of mirtazapine or placebo for 28 days. Insomnia severity improved more on mirtazapine — though six people stopped because of adverse effects, against one on placebo.2

In DREAMING, 80 adults whose main problem was staying asleep took low-dose mirtazapine, low-dose amitriptyline, or placebo. At six weeks, about half of those on mirtazapine had a clinically relevant improvement, against 14% on placebo. From twelve weeks onwards there was no significant difference from placebo, and the authors suggest considering it for around six weeks.3

So: a short-term effect that does not clearly persist. The European insomnia guideline reflects that, saying low-dose sedating antidepressants can be considered off-label for the short-term treatment of insomnia, while keeping CBT-I first-line regardless of what else is going on.4

Mirtazapine is also not among the fourteen agents graded in the AASM's 2017 insomnia medication guideline, and it is not cited anywhere in it, so that guideline makes no recommendation on it either way.5 For chronic insomnia, US guidelines still put CBT-I first.67 Whether mirtazapine makes sense for you is a conversation with your prescriber.

If you are taking it and sleeping badly anyway

That is not unusual. If you have both depression and chronic insomnia, you can be reliably knocked out at 11pm and still wake at 3am with the same racing mind you had before.

If that is the pattern, the insomnia may be a condition in its own right rather than a symptom that will clear when the depression lifts — and it may need treating alongside the depression rather than after it.

CBT-I does not interact with mirtazapine and does not require stopping it. If you and your prescriber later decide to taper, having the behavioral skills already in place tends to make that easier.