Mirtazapine is one of those medications that seems to live a double life. To primary-care physicians, it is an antidepressant that helps with sleep and appetite. To psychiatrists, it is a Swiss-army-knife adjunct: useful for some patients with schizophrenia who have stubborn negative symptoms, akathisia they cannot shake, persistent depression alongside their psychosis, insomnia, or significant weight loss. The evidence is more interesting than headlines usually suggest.
Mirtazapine is a sedating antidepressant with a unique receptor profile that, when added to an antipsychotic, may modestly improve negative symptoms, akathisia, sleep, and appetite for some patients.
What mirtazapine is
Mirtazapine, marketed as Remeron, is sometimes called a NaSSA (noradrenergic and specific serotonergic antidepressant). It blocks alpha-2 adrenergic autoreceptors, which increases noradrenaline and serotonin release. It also blocks several serotonin receptor subtypes (5-HT2A, 5-HT2C, 5-HT3) and has potent histamine H1 blockade — which is why it is so sedating and so good at increasing appetite.
The reasons it is added in schizophrenia
1. Negative symptoms
Several small randomised trials and meta-analyses, including a frequently cited 2014 review in Schizophrenia Bulletin, have suggested that mirtazapine added to a stable antipsychotic regimen modestly improves negative symptoms — flat affect, low motivation, social withdrawal — over weeks to months. Effects are not dramatic, but for symptoms that are otherwise hard to treat, even modest help can be meaningful. See our background piece on positive vs negative symptoms and CBTp for negative symptoms for non-medication options.
2. Akathisia
Low-dose mirtazapine (often 15 mg at bedtime) has emerged as an alternative to propranolol for antipsychotic-induced akathisia. Several head-to-head and placebo-controlled studies suggest comparable efficacy. It is particularly attractive for patients who can't take beta-blockers due to asthma, low blood pressure, or other contraindications.
3. Depression
Depression is common in schizophrenia, both as a symptom and as a separate diagnosis. Mirtazapine's antidepressant effects are well-established in unipolar depression, and many clinicians use it cautiously when patients with schizophrenia or schizoaffective disorder have prominent depressive symptoms.
4. Sleep
Antipsychotics commonly disturb sleep. Mirtazapine is strongly sedating at low doses (paradoxically more sedating at lower doses, due to relative dominance of antihistamine effects), and is often used to improve sleep without resorting to long-term hypnotics. See our broader guide to sleep hygiene in schizophrenia.
5. Appetite and weight
Mirtazapine reliably increases appetite and weight. In someone with antipsychotic-induced weight gain, this is a downside. But in a patient who has lost significant weight from a relapse, or whose appetite has been suppressed by aripiprazole or stimulant comedications, it can be useful.
How it is typically used
For most augmentation indications, mirtazapine is started at 15 mg at bedtime. Some prescribers go up to 30 or 45 mg, but at higher doses the noradrenergic effects start to outweigh the antihistamine effects, and the medication can become more activating and less sedating. Onset for mood and negative symptoms is usually two to six weeks; for sleep and appetite, often within days.
Side effects
- Sedation — almost universal, often the goal
- Weight gain and appetite increase — common; needs honest discussion if the antipsychotic is already causing weight problems
- Dry mouth
- Constipation — modest
- Dizziness
- Vivid dreams
- Rare: agranulocytosis (a black-box concern, but extremely uncommon), serotonin syndrome (when combined with other serotonergic drugs), restless legs
You develop a new fever, sore throat, or signs of infection (possible neutropenia); marked agitation or worsening depression; or signs of serotonin syndrome (high fever, muscle rigidity, confusion) when combined with other serotonergic medications.
Drug interactions worth knowing
Mirtazapine is generally well-behaved with antipsychotics. The combination with clozapine has been particularly studied, and is often used to mitigate weight loss in cachectic patients while clozapine is being titrated. Combinations with other sedating medications (benzodiazepines, alcohol, opioids) compound sedation. Combinations with serotonergic medications (SSRIs, SNRIs, tramadol, MAOIs) raise the risk of serotonin syndrome.
The honest summary
Mirtazapine is not a transformative medication. It is a thoughtful add-on in a few well-defined situations: stubborn negative symptoms, akathisia that won't budge, comorbid depression, severe insomnia, weight loss. Its biggest practical drawbacks are sedation and weight gain, but in many patients those are features rather than bugs. For someone with antipsychotic-induced weight gain who is struggling, it is usually the wrong choice — see metformin for antipsychotic-induced weight gain instead.
Discontinuation
Mirtazapine should be tapered rather than stopped abruptly. Withdrawal symptoms can include nausea, irritability, dizziness, insomnia, and flu-like feelings.
This article is for educational purposes only and is not medical advice, diagnosis, or treatment. Always consult a qualified mental health professional. If you or someone you know is in crisis, call or text 988 in the US, or your local emergency number.