Quick Answer: Mirtazapine (brand name Remeron) is an antidepressant prescribed off-label for insomnia in Canada, but it is not Health Canada approved for sleep disorders. It works by blocking histamine receptors, causing sedation. Lower doses (7.5–15 mg) are more sedating than higher doses. Canadian guidelines recommend CBT-I (Cognitive Behavioural Therapy for Insomnia) as first-line treatment before any medication, including mirtazapine.
In This Guide
Reading Time: 11 minutes
Medical Disclaimer: This article is for general information only. Mirtazapine is a prescription medication. It is not a substitute for advice from your doctor, pharmacist, or other qualified health professional. Do not start, stop, or change any medication without medical supervision.
If you've been having trouble sleeping, your doctor may have mentioned mirtazapine. Or perhaps you've come across it while looking into sleep medications online. It's one of those drugs that comes up often in conversations about insomnia, despite the fact that it was never designed as a sleep aid.
What follows is a plain-language look at what mirtazapine is, how it affects sleep, what the current evidence says, and what Canadian clinical guidelines actually recommend. At Mattress Miracle, we spend our days helping Brantford residents sleep better. We're not pharmacists, but we believe informed patients ask better questions. Consider this a starting point for a conversation with your doctor.
What Is Mirtazapine?
Mirtazapine is an antidepressant belonging to a class called NaSSAs (noradrenergic and specific serotonergic antidepressants). In Canada, it is sold under the brand name Remeron, as well as several generics: APO-Mirtazapine, Auro-Mirtazapine, SANDOZ Mirtazapine, and TEVA-Mirtazapine, among others.
Health Canada has approved mirtazapine for the treatment of major depressive disorder. It is not approved for insomnia. When a physician prescribes it specifically for sleep, they are doing so "off-label," which is legal and common in Canadian medical practice, but it means the evidence base is thinner than for approved indications.
Mirtazapine has been available in Canada since the late 1990s. It's an older drug by pharmaceutical standards, which means there's a reasonable body of research, including Canadian-specific evaluations from the Therapeutics Initiative at UBC, an independent drug evaluation group that advises BC PharmaCare and is widely cited across Canadian provinces.
How Mirtazapine Works for Sleep
To understand why mirtazapine makes people sleepy, you need a brief look at its pharmacology.
Mirtazapine blocks several receptor types simultaneously. The one most relevant to sleep is the H1 histamine receptor. Histamine is a wakefulness-promoting neurotransmitter; block the receptors that respond to it, and sedation follows. This is the same basic mechanism behind classic antihistamines like diphenhydramine (Benadryl), though mirtazapine's H1 binding affinity is considerably stronger.
It also blocks alpha-2 adrenergic receptors (which boosts norepinephrine and serotonin release) and certain serotonin receptor subtypes. These additional effects are responsible for its antidepressant properties and, as we'll see below, for a somewhat counterintuitive dose-sedation relationship.
Mirtazapine's Receptor Targets
| Receptor | Effect When Blocked | Relevant to Sleep? |
|---|---|---|
| H1 (histamine) | Sedation, drowsiness | Yes, directly |
| Alpha-2 adrenergic | Increased norepinephrine (activating) | Counteracts sedation at higher doses |
| 5-HT2A / 5-HT2C serotonin | Anxiolytic, appetite stimulation | Indirect (reduces anxiety; drives weight gain) |
| Muscarinic (weak) | Dry mouth, constipation | No, but relevant to side effects |
Source: Stahl SM. Stahl's Essential Psychopharmacology. 4th ed. Cambridge University Press, 2013; StatPearls [NCBI Bookshelf].
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The Low-Dose Sedation Paradox
Here's something that surprises many patients and even some clinicians: with mirtazapine, lower doses tend to be more sedating than higher doses.
This seems backwards. More drug, more effect, right? Not in this case.
At low doses (7.5 mg or 15 mg), the H1 histamine blockade dominates. The sedating effect is strong. As the dose increases above 15 mg, the alpha-2 adrenergic blockade becomes more prominent, which triggers a surge of activating neurotransmitters, norepinephrine and dopamine, that partially cancel out the sedation. The net result: higher doses are often less sedating, not more.
The Dose-Sedation Relationship
Research from the UCLA Proceedings and the Journal of Clinical Psychopharmacology confirms a weak but consistent inverse relationship between mirtazapine dose and sedation at doses above 15 mg. When prescribed specifically for sleep, physicians typically use 7.5 mg to 15 mg nightly rather than the standard antidepressant doses (15–45 mg).
There's a further complication: tolerance. Several studies, including a review in Frontiers in Psychiatry, found that sedation tends to decrease over time regardless of whether the dose remains fixed or is titrated. For some patients, the sleep-promoting effects may weaken over weeks or months, limiting mirtazapine's usefulness as a long-term solution.
What the Evidence Shows
How well does mirtazapine actually work for insomnia? The honest answer is: it produces measurable improvements in some sleep outcomes in the short term, but the evidence for longer-term use is limited.
The DREAMING Trial (2024)
The most recent and methodologically rigorous study is the DREAMING trial, a randomised double-blind placebo-controlled trial published in 2024 examining low-dose mirtazapine for insomnia in general practice settings. Published in a leading peer-reviewed journal, it found that a 28-day course of mirtazapine significantly reduced insomnia severity as measured by the Insomnia Severity Index (ISI), with improvements in wake after sleep onset, total sleep time, and sleep efficiency compared to placebo.
However, the study authors cautioned that results do not support prescribing mirtazapine for several months in insomnia disorder. They suggested physicians consider it as a short-term option (roughly six weeks) only when non-pharmacological treatments have proven insufficient. (DREAMING trial, PMC, 2024)
The MIRAGE Study (Older Adults)
The MIRAGE study, a randomised double-blind placebo-controlled trial focused on older adults with chronic insomnia, also found mirtazapine superior to placebo on insomnia measures. This is clinically relevant because older Canadians are disproportionately affected by both insomnia and depression, and a medication that may address both is appealing to prescribers. (PubMed, MIRAGE study)
BC Therapeutics Initiative Assessment (Canada)
The most important Canadian-specific evaluation comes from Therapeutics Initiative Letter #129 (2021), an independent, industry-free drug review produced at UBC. Their conclusions are characteristically measured:
- Mirtazapine shows a statistically significant antidepressant effect compared to placebo, but the clinical magnitude is modest
- For sleep specifically, somnolence occurs in approximately 50% of study participants, which is why off-label prescribing happens, but evidence for this use is not well-established
- The dose-response relationship is complex and not well-characterised in RCT data
- Weight gain risk is significant and clinically meaningful
The Therapeutics Initiative does not endorse mirtazapine as a sleep medication. Their review reflects the broader Canadian clinical consensus that CBT-I should be tried before any pharmacological intervention for insomnia.
Dorothy, Sleep Specialist at Mattress Miracle: "We hear from customers fairly often who've been prescribed mirtazapine or another medication for sleep. What surprises them is that the research points to behaviour and environment changes first. A medication might help you fall asleep, but if your mattress is uncomfortable or your bedroom is running too warm, you're still not getting quality sleep. The two don't cancel each other out."
Side Effects Canadians Should Know
Mirtazapine carries a side effect profile that requires honest consideration. These are not rare or theoretical; they occur frequently enough to influence prescribing decisions.
Weight Gain
This is the most clinically significant concern. A large UK cohort study following patients across 12 antidepressants found that mirtazapine produced the greatest adjusted rate ratio for weight gain (1.50; 95% CI 1.45–1.56) among all antidepressants studied. The mechanism involves both serotonin 5-HT2C blockade (which increases appetite) and H1 blockade (which reduces calorie burning through sedation). Weight gain is not a trivial concern, as it can contribute to sleep apnea, joint discomfort, and metabolic issues that independently worsen sleep quality.
Daytime Sedation
While sedation is the intended effect at night, some patients experience carry-over grogginess the next day. This is more common at the 7.5–15 mg range used for sleep. The half-life of mirtazapine is 20–40 hours, meaning it stays in the body far longer than a typical sleep-specific medication.
Dry Mouth and Constipation
Anticholinergic-like effects cause dry mouth in a significant proportion of users, along with constipation. These are typically manageable but can be bothersome over time.
Tolerance to Sedative Effects
As noted above, sedation often diminishes with continued use. Some patients find they need increasing doses to achieve the same sleep effect, which then brings in more side effects from the higher dose while paradoxically reducing the sedation they wanted.
Discontinuation
Stopping mirtazapine abruptly can cause withdrawal-like effects including anxiety, insomnia rebound, nausea, and dizziness. Canadian prescribers typically recommend gradual tapering under medical supervision.
Rare but Serious: Agranulocytosis
There is a rare risk of agranulocytosis (dangerous drop in white blood cells), which is why persistent fever, sore throat, or mouth sores during mirtazapine treatment should be reported to a physician promptly. This risk is low but warrants awareness.
Mirtazapine Side Effect Summary
| Side Effect | Frequency | Notes |
|---|---|---|
| Somnolence (daytime sleepiness) | ~50% of RCT participants | May carry over into daytime hours |
| Weight gain | Common; highest among antidepressants | Can worsen sleep apnea risk |
| Dry mouth | Common | Manageable, often improves over time |
| Constipation | Common | Dietary fibre and hydration help |
| Dizziness | Moderate | Fall risk in older adults |
| Sedation tolerance | Reported across multiple studies | Sleep benefit may fade within weeks |
| Agranulocytosis | Rare | Seek medical attention for persistent fever |
Sources: Stahl 2013; Therapeutics Initiative #129, 2021; StatPearls [NCBI Bookshelf].
Mirtazapine vs Other Sleep Options in Canada
Mirtazapine is one of several medications used off-label or on-label for insomnia in Canada. Understanding the landscape helps patients have better conversations with their physicians.
CBT-I: The Recommended First Step
Canadian clinical guidelines are clear: Cognitive Behavioural Therapy for Insomnia (CBT-I) is the first-line treatment for chronic insomnia, before any pharmacological intervention. The 2024 updated recommendations published in Canadian Family Physician reaffirm this position, as does the Delphi consensus statement from Canadian sleep experts published in 2024. Health Quality Ontario's Insomnia Disorder Quality Standard (updated 2025) states that people with insomnia disorder should have timely access to CBT-I before medication.
Despite this, a Canadian study found that only 17% of Ontario clinicians regularly offer CBT-I to patients with insomnia, while 64% recommend sleep hygiene alone. If your physician hasn't mentioned CBT-I, it's worth raising. You can also explore digital CBT-I programs, which Health Quality Ontario has flagged as an acceptable alternative for those without access to in-person therapy.
Mattress Miracle has published a local resource on CBT-I practitioners in Ontario for Brantford-area residents who want to explore this option.
Zopiclone
Zopiclone (brand name Imovane) is Health Canada approved for short-term insomnia management. It works quickly and effectively for sleep onset and maintenance. The Therapeutics Initiative, however, has raised concerns about its use, noting dependency risk, rebound insomnia on discontinuation, and limited evidence supporting long-term benefit. It is generally recommended for 2–4 weeks maximum.
Trazodone
Trazodone is another antidepressant used off-label for sleep, with a similar mechanism to mirtazapine (H1 blockade, serotonin effects). The Therapeutics Initiative Letter on zopiclone and trazodone notes that evidence for both is weak for primary insomnia, and both carry risks of dependence-like patterns and side effects. Trazodone causes less weight gain than mirtazapine but can cause orthostatic hypotension (dizziness when standing), a particular concern for older adults.
Melatonin
Low-dose melatonin (0.5–3 mg) is available over the counter in Canada and is most effective for circadian rhythm disruptions such as jet lag and shift work. Evidence for primary chronic insomnia is limited. Melatonin is considered safe for most adults and has no significant interaction profile, making it a reasonable first step for mild, situational sleep issues before pursuing a prescription.
Doxylamine
Doxylamine (Unisom) is an antihistamine available over the counter in Canada, sometimes used for short-term sleeplessness. It has the same H1 blockade mechanism as mirtazapine. Tolerance develops quickly (within a few days), and it can cause significant morning grogginess, particularly in older adults.
Sleep Medication Comparison: Canadian Context
| Option | Health Canada Approved for Insomnia? | Key Concerns | Evidence Quality |
|---|---|---|---|
| CBT-I | N/A (therapy) | Access, cost, commitment | Strong; long-lasting effects |
| Mirtazapine (Remeron) | No (off-label) | Weight gain, tolerance, long half-life | Moderate; short-term only |
| Zopiclone (Imovane) | Yes (short-term) | Dependency, rebound insomnia | Moderate; not for chronic use |
| Trazodone | No (off-label) | Orthostatic hypotension, weak evidence | Limited |
| Melatonin (OTC) | Regulated as NHP | Weak for primary insomnia | Moderate for circadian issues only |
| Doxylamine (OTC) | Not specifically | Rapid tolerance, morning grogginess | Limited |
Your Sleep Environment Matters Too
One point that often gets overlooked when people focus on sleep medications: a pill can only do so much if the conditions for sleep are working against you.
The Mattress Miracle Perspective on Sleep Aids
We've been helping Brantford families sleep better since 1997. We're a mattress store, not a pharmacy, so we can't advise you on medications. But we do know that many customers come to us after trying medication for sleep without addressing the basics: uncomfortable mattresses, heat retention, poor spinal support.
Sleep medications work best as a bridge, not a permanent solution. The goal for most people is sustainable, medication-free sleep. That usually involves better sleep habits (CBT-I principles) and, often, a sleeping surface that actually supports your body through the night.
If you're in Brantford and want to talk about how mattress comfort might be affecting your sleep, Brad and our team are always happy to have that conversation at 441 1/2 West Street.
The science of sleep hygiene overlaps considerably with CBT-I principles. A few basics that Canadian sleep researchers consistently highlight:
- Temperature: The bedroom should be 16–19°C for most adults. Body temperature drops naturally during sleep onset, and a cooler room supports this.
- Consistent schedule: Going to bed and waking at the same time strengthens circadian rhythm, which is the single most evidence-backed behavioural intervention for insomnia.
- Mattress comfort: Chronic discomfort from an unsupportive mattress creates micro-arousals throughout the night that reduce sleep quality even when total sleep time looks acceptable.
- Light control: Blackout curtains matter. Artificial light, especially blue-spectrum light from phones and devices, suppresses melatonin production.
- Stimulus control: Use the bed only for sleep and intimacy. Watching TV, scrolling, or working in bed trains the brain to associate the bed with wakefulness.
These aren't alternatives to treating genuine insomnia disorder. But they're the foundation without which no medication, including mirtazapine, performs at its best.
Brad, Owner, 40+ years of experience: "People sometimes ask if a new mattress can replace their sleep medication. That's not a fair question. What I'd say is: if your medication is working but you're still waking up with back pain or waking up too hot, your mattress might be undoing some of the good that medication is doing. The two things are related."
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Call 519-770-0001Frequently Asked Questions
Is mirtazapine effective for sleep if I don't have depression?
Short-term evidence suggests it improves certain sleep measures in people with primary insomnia, even without depression. The DREAMING trial (2024) found significant improvement in sleep outcomes over 28 days versus placebo. However, it is not Health Canada approved for insomnia, the evidence is weaker than for its antidepressant use, and Canadian guidelines recommend exhausting non-pharmacological options first. Talk to your doctor about whether it makes sense for your specific situation.
Why does my doctor prescribe such a low dose of mirtazapine for sleep?
Counterintuitively, lower doses (7.5–15 mg) produce stronger sedation than higher antidepressant doses (30–45 mg). At low doses, the H1 histamine-blocking effect dominates, causing drowsiness. At higher doses, activating noradrenergic effects partially counteract the sedation. Prescribing a low dose for sleep is an intentional, pharmacologically rational choice, not an error or conservative starting point that needs increasing.
Will mirtazapine make me gain weight?
Weight gain is a well-documented side effect of mirtazapine and one of the most clinically significant. A large study following patients across 12 antidepressants found mirtazapine associated with the highest rate of weight gain. The mechanism involves appetite stimulation through serotonin receptor blockade and metabolic slowing through H1 blockade. This is a real risk to discuss with your doctor before starting, especially if you have pre-existing weight-related health concerns.
Can I stop taking mirtazapine suddenly?
It is not recommended to stop mirtazapine abruptly. Discontinuation effects can include rebound insomnia, anxiety, nausea, dizziness, and flu-like symptoms. Canadian prescribers typically recommend gradual tapering under medical supervision. The timeframe for tapering depends on how long you've taken it and your dose. Always consult your prescribing physician before making changes.
What is CBT-I and why do Canadian guidelines recommend it before mirtazapine?
CBT-I (Cognitive Behavioural Therapy for Insomnia) is a structured psychological treatment that addresses the thoughts and behaviours that perpetuate chronic insomnia. It typically involves stimulus control, sleep restriction, cognitive restructuring, sleep hygiene, and relaxation techniques, delivered over 6–8 sessions. Unlike medication, CBT-I produces durable improvements that persist after treatment ends. Canadian clinical guidelines, including the 2024 Canadian Family Physician recommendations and Health Quality Ontario's 2025 Insomnia Quality Standard, identify CBT-I as first-line treatment for chronic insomnia because its long-term outcomes exceed those of pharmacotherapy with fewer risks.
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Phone: (519) 770-0001
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If chronic sleep issues have you researching medications online, your mattress and sleep environment might be contributing to the problem. Stop by and let Brad or Dorothy walk you through what we carry. A comfortable, well-supported mattress won't replace a doctor's advice, but it removes one major barrier to the sleep you need.
Related Reading
- CBT-I Practitioners in Ontario: A Guide for Brantford Residents
- Do Sleep Patches Work? Melatonin Patches, Transdermal Delivery, and What the Evidence Says
- Theories of Sleep: What Scientists Say Happens When We Sleep
- Sleeping with a Mouthguard: Bruxism, Sleep Apnea, and What to Expect
- Browse Mattresses at Mattress Miracle Brantford
- Haven Sleep Co. Review: What Canadians Should Know Before Buying Online
Sources
- Therapeutics Initiative. Mirtazapine: Update on efficacy, safety, dose response. TI Letter #129, May 2021. University of British Columbia. ti.ubc.ca
- Riemann D, et al. Effectiveness of low-dose mirtazapine in patients with insomnia disorder: the DREAMING trial. PMC, 2024. PMC12199994
- Frase L, et al. Mirtazapine for chronic insomnia in older adults: the MIRAGE study. PubMed, 2024. PubMed 40135470
- Anttila SAK, Leinonen EVJ. A review of the pharmacological and clinical profile of mirtazapine. StatPearls, NCBI Bookshelf. NBK519059
- Serretti A, Mandelli L. Antidepressants and body weight. Journal of Clinical Psychiatry, 2010. Referenced in Therapeutics Initiative #129.
- Stahl SM. Stahl's Essential Psychopharmacology. 4th ed. Cambridge University Press, 2013.
- Arroll B, et al. Treatment of chronic insomnia in adults. Canadian Family Physician 70(3), March 2024. cfp.ca
- Morin CM, et al. Delphi consensus recommendations for the management of chronic insomnia in Canada. Sleep Medicine, 2024. ScienceDirect
- Therapeutics Initiative. Improving how we prescribe zopiclone and trazodone for insomnia. NCBI Bookshelf. NBK618769
- Yoon HW, et al. Tachyphylaxis to the sedative action of mirtazapine. Frontiers in Psychiatry, 2018. PMC5907691
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