Mental health
Mirtazapine
A noradrenergic and specific serotonergic antidepressant (NaSSA) — An antidepressant that often helps sleep and appetite — useful when those are a problem.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
What it is
Mirtazapine is an antidepressant often chosen when low mood is accompanied by insomnia or poor appetite, or when other antidepressants have caused troublesome side-effects.
How it works
It works differently from SSRIs — boosting noradrenaline and serotonin signalling through a distinct receptor mechanism. Blocking histamine receptors explains the sedation and increased appetite that can be clinically useful.
In practice
In practice mirtazapine earns its place where depression comes with poor sleep and poor appetite, since its sedating and appetite-stimulating effects can be turned to advantage — typically taken at night. Counterintuitively the sedation can be more pronounced at lower doses. It is weight-gaining, so it suits some patients and not others, and as with all antidepressants we watch mood closely early on and taper rather than stop abruptly. A rare but important warning is to report signs of infection, because of an uncommon effect on white cells.
Examples
Practical use
How to take it & use it well
- Take mirtazapine once daily, usually at night, as it often causes drowsiness that can actually help with sleep.
- It can be taken with or without food; orodispersible tablets are placed on the tongue to melt and then swallowed with saliva.
- Keep taking it every day, as it can take a few weeks to feel the full benefit on mood, and do not judge it by the first few days.
- Lower, sedating effects can be more noticeable at first; tell your clinician if heavy daytime drowsiness does not settle.
- Report any new sore throat, fever, mouth ulcers or signs of infection promptly, as rarely this medicine can affect blood cells.
- Do not stop suddenly after regular use; your clinician will help you reduce gradually to avoid discontinuation symptoms.
Common uses
- Depression, particularly with insomnia or poor appetite
- Alternative when SSRIs/SNRIs are not tolerated
Monitoring
- Mood and any suicidal ideation, especially early and in the young
- Weight
- Full blood count if signs of infection appear
Weighing it up
Advantages & disadvantages
Advantages
- It treats depression and can be especially helpful when poor sleep and poor appetite are prominent.
- Taken at night, its sedating effect can improve sleep without a separate sleeping tablet.
- It is less likely than some antidepressants to cause sexual side effects or stomach upset.
- The melt-in-the-mouth form is useful for people who find swallowing tablets difficult.
Disadvantages
- Drowsiness and a hangover-like feeling are common, particularly at the start.
- Increased appetite and weight gain are frequent and can be unwelcome.
- Like other antidepressants, mood or thoughts of self-harm can briefly worsen early in treatment, especially in younger people.
- It can rarely affect blood cell counts, so signs of infection should be reported.
Key safety principles
What to watch for
- Sedation and weight gain are common (and sometimes the reason it is chosen).
- Rare bone-marrow effects — report sore throat, fever or signs of infection.
- Monitor mood early in treatment; taper to stop rather than stopping abruptly.
Key interactions
What to avoid or check alongside
- Alcohol and other sedating medicines add to drowsiness and impaired alertness.
- Combining with other serotonin-raising medicines, including some antidepressants, triptans or tramadol, can risk serotonin syndrome.
- Monoamine oxidase inhibitors must not be used close to mirtazapine because of a serious interaction.
- Strong enzyme-inducing or inhibiting medicines can lower or raise mirtazapine levels.
- Medicines that can prolong the heart's QT interval may add to a small risk when combined.
Patient & carer advice
- Usually taken at night because it can make you drowsy
- It may increase appetite and weight — tell us if that troubles you
- Report any sore throat, fever or mouth ulcers
Use with
Related clinical calculators
Dose and risk decisions for this class often depend on renal function, weight or bleeding/stroke risk. These tools help:
Answers
Mirtazapine: frequently asked questions
Why is mirtazapine taken at night?
Mirtazapine often causes drowsiness, so taking it at bedtime turns that into a benefit by helping with sleep and reducing daytime sleepiness. If it still leaves you groggy in the morning, tell your clinician.
Does mirtazapine cause weight gain?
Increased appetite and weight gain are common with mirtazapine. Eating mindfully and staying active can help. If weight gain becomes a concern, discuss it with your prescriber rather than stopping the medicine on your own.
How long does mirtazapine take to work?
Sleep and appetite may improve within days, but the full effect on mood usually takes a few weeks. Keep taking it regularly, and contact your clinician if you feel worse or have distressing thoughts early in treatment.
Can I stop mirtazapine when I feel better?
Do not stop suddenly. Antidepressants are usually continued for a period after you feel well to reduce relapse, and stopping abruptly can cause discontinuation symptoms. Your clinician will guide a gradual reduction when the time is right.
Is it safe to drink alcohol on mirtazapine?
Alcohol adds to the drowsiness and slowed reactions that mirtazapine can cause, so it is best avoided or kept to a minimum. Be especially careful about driving or using machinery if you have been drinking.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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