Drug info

Mirtazapine

Antidepressant (NaSSA) Prescription only

A night-time antidepressant that often brings sleepiness and a bigger appetite. A bonus for some, a problem for others.

At a glance

For
Depression (low doses sometimes used for sleep, off-label)
Works
Similar to other antidepressants: about half improve a lot, versus about a third on a dummy treatment. Sleep and appetite often improve in the first week
Cost
Under the $25 PBS co-payment, about $22–24 a month for generics (brand premium extra); $7.70 concession
Kicks in
Sleep within days; mood in 2–4 weeks
Taken for
Usually 6–12 months after feeling well
Watch for
Drowsiness, bigger appetite and weight gain, dry mouth, next-day grogginess

The 2 am fridge raid is a genuine side effect. Plan your snacks before they plan you.

Brand names

How it works

It blocks alpha-2 receptors, boosting noradrenaline and serotonin. A strong antihistamine effect causes sleepiness and a bigger appetite.

Used for

Side effects

Full side-effect list (from the product information)

How often, from the official product information. Bold = serious.

Very common more than 1 in 10

  • Weight gain and increased appetite
  • Drowsiness or sedation
  • Headache
  • Dry mouth

Common 1 in 10 to 1 in 100

  • Odd dreams, confusion, anxiety
  • Poor sleep, sluggishness, tremor
  • Dizziness, memory problems
  • Nausea, diarrhoea, vomiting, constipation
  • Rash, joint, muscle or back pain
  • Swollen ankles, tiredness

Uncommon 1 in 100 to 1 in 1,000

  • Nightmares, agitation, restlessness
  • Hallucinations, mania
  • Pins and needles, restless legs
  • Fainting, low blood pressure
  • Numb mouth

Rare 1 in 1,000 to 1 in 10,000

  • Aggression
  • Muscle jerks
  • Pancreatitis
  • Raised liver enzymes

Frequency not known reported, rate unclear

  • Bone marrow suppression
  • Low sodium, suicidal thoughts
  • Seizures, serotonin syndrome
  • Severe skin reactions
  • Muscle breakdown, sleepwalking
  • Breast swelling or milk discharge
  • Urine retention, prolonged erection

Get help urgently if

Good to know

Support lines

If you or someone else is in danger right now, call your emergency number. To talk to someone, any time:

Common questions

Does mirtazapine cause weight gain?

Yes. Weight gain and increased appetite are very common, affecting more than 1 in 10 people.

Is mirtazapine used for sleep?

Low doses are sometimes used for sleep problems, but this is off-label and not a first choice because of weight gain and next-day drowsiness.

When should I take mirtazapine?

At bedtime. Don’t drive until you know you’re not drowsy the next day.

How long does mirtazapine take to work?

Sleep and appetite often improve within the first week. The effect on mood usually starts after 2 to 4 weeks, with full benefit by 6 to 8 weeks.

What are the side effects of mirtazapine?

Drowsiness, increased appetite, weight gain and dry mouth are the most common. Rarely it lowers white blood cells, so see your doctor promptly if you get a fever, sore throat or mouth ulcers.

How do I stop mirtazapine?

Reduce it slowly with your doctor over a few weeks. Stopping suddenly can cause poor sleep, nausea, anxiety and dizziness.

Information only. Not a recommendation or endorsement of any product. Whether a medicine suits you depends on your health and other medicines, so talk to your doctor or pharmacist. In an emergency, call 000 (Australia) or your local emergency number. From a mobile, 112 works in most countries.

More information

Updated 28 October 2026.

Related

maladywise.com/medicines/mirtazapine/