Mirtazapine NHS: everything you need to know

Mirtazapine is an antidepressant. It belongs to a group of medicines called noradrenergic and specific serotonergic antidepressants (NaSSAs). It has been available in the UK since 1997.

The NHS widely prescribes it.

How mirtazapine works:

Mirtazapine works in a complex way:

• Alpha-2 adrenergic antagonist: It blocks alpha-2 receptors. This increases noradrenaline and serotonin release.
• 5-HT2A, 5-HT2C and 5-HT3 antagonist: It blocks specific serotonin receptors. This helps with depression and stops nausea.
• H1 histamine receptor antagonist: This causes its sedating and appetite-stimulating effects.

Mirtazapine increases noradrenaline and serotonin in the brain. It does this differently from SSRIs, like sertraline or fluoxetine. It also differs from SNRIs, like venlafaxine.

What mirtazapine is prescribed for:

• Depression: This is its main approved use.
• Anxiety: Doctors often use it when anxiety is strong with depression. This is an 'off-label' use.
• Insomnia with depression: It can make you sleepy. This makes it a good choice if you have trouble sleeping.
• Appetite stimulation: It can help older or unwell patients eat more.

Mirtazapine comes as standard tablets, orodispersible tablets, and an oral solution. Orodispersible tablets dissolve on your tongue. All are available on the NHS.

Dosing schedule:

• Starting dose: Take 15 mg once daily at bedtime.
• Dose increases: If it does not work well after 2 to 4 weeks, your dose may increase to 30 mg.
• Maximum dose: The highest dose is 45 mg once daily.
• Elderly patients: They take the same doses. However, dose increases should be slower and closely watched.

Practical tips:

• Take mirtazapine at the same time each day. This should be 1 to 2 hours before bedtime.
• You can take it with or without food.
• Swallow standard tablets whole with water.
• Place orodispersible tablets on your tongue. Let them dissolve. You do not need water.
• If you miss a dose, take it when you remember. Do not take it if it is almost time for your next dose. Never take a double dose.

How long until it works:

• You may notice better sleep and appetite within the first week.
• The full antidepressant effect usually takes 2 to 4 weeks.
• NICE advises continuing treatment for at least 6 months after recovery. This lowers the risk of relapse.
• Do not stop taking mirtazapine without talking to your prescriber.

The NHS lists these side effects for mirtazapine. Most are manageable. They often get better as you continue treatment.

Common side effects:

• Increased appetite and weight gain.
• Drowsiness or sleepiness, especially at lower doses.
• Headaches.
• Dry mouth.
• Constipation.
• Feeling dizzy or faint.
• Swelling in the feet or ankles.

Less common but important side effects:

• Vivid or unusual dreams.
• Joint pain or muscle aches.
• Tremor.
• Restless legs.

Serious side effects requiring medical attention:

• Yellowing of the eyes or skin (jaundice).
• Fever with a sore throat or mouth ulcers. This could be a blood disorder.
• Thoughts of self-harm or suicide.
• Fits or seizures.
• Allergic reactions, such as rash, swelling, or breathing problems.

For more details on mirtazapine side effects, see our side effects guide.

You can report any suspected side effects. Use the Yellow Card Scheme at yellowcard.mhra.gov.uk.

Mirtazapine interacts with other medicines. It is not suitable for everyone.

Important drug interactions:

• MAOIs (e.g., phenelzine, tranylcypromine): Do not take these within 14 days of mirtazapine. This combination can cause serotonin syndrome.
• Other serotonergic drugs (SSRIs, SNRIs, tramadol, triptans, St John's wort): Combining these with mirtazapine increases the risk of serotonin syndrome.
• Benzodiazepines and Z-drugs: These cause more sedation when taken together.
• Alcohol: It enhances the sedating effects.
• Warfarin: Mirtazapine may increase its blood-thinning effect. Your INR should be monitored.

Cautions:

• Epilepsy: Mirtazapine may lower the seizure threshold.
• Liver or kidney impairment: Your body may clear the drug slower. You might need a dose adjustment.
• Diabetes: Weight gain and metabolic effects may worsen blood sugar control.
• Cardiac disease: Use with caution if you have heart conduction problems.
• Urinary retention or prostatic hypertrophy: Mirtazapine may worsen symptoms.
• Angle-closure glaucoma: Mirtazapine has mild anticholinergic effects.

Pregnancy and breastfeeding:

Use mirtazapine in pregnancy only if benefits outweigh risks. It passes into breast milk. Seek specialist advice.

The patient, prescriber, and ideally a perinatal psychiatrist should make the decision.

Do not stop mirtazapine suddenly. The NHS and BNF recommend a gradual dose reduction. This helps minimise withdrawal effects.

Possible withdrawal symptoms:

• Dizziness and headache.
• Nausea and vomiting.
• Anxiety and agitation.
• Insomnia and vivid dreams.
• Irritability.
• Paraesthesia, such as tingling or 'electric shock' feelings.
• Flu-like symptoms.

Recommended approach:

• Reduce the dose gradually over at least 4 weeks. Take longer if you have used mirtazapine for a long time.
• NICE suggests some patients may need several months. They should use smaller dose decreases.
• If withdrawal symptoms are bad, slow the taper. Or, temporarily return to the previous dose.
• Stay in touch with your GP during withdrawal.

When to consider stopping:

• After at least 6 months of feeling well for a first episode of depression.
• After at least 2 years of feeling well for recurrent depression.
• You and your prescriber should make this decision together.

Some patients find the withdrawal process hard. They may benefit from extra support. This includes counselling or cognitive behavioural therapy during the taper.