Mirtazapine

Generic name

Mirtazapine

Active ingredient

Mirtazapine

Product type

Small-molecule medicine

Drug class

NaSSA antidepressants

Brand names

UK Mirtazapine

Routes

Oral

Dosage forms

Tablet, Solution

Usual preparations

Comes as tablets, tablets that melt on the tongue (orodispersible tablets), and an oral solution. (summary of the cited reference, not a prescription)

Onset and duration

The NHS says an improvement may be seen after a week, although it usually takes 4 to 6 weeks to feel the full benefits.

Monitoring

The manufacturer's UK leaflets advise a prompt blood test if signs of infection such as fever, sore throat or mouth ulcers appear. The NHS advises against stopping suddenly, and says the dose is usually reduced gradually when the medicine is stopped.

Availability by country

Legal status differs between countries and can change; each row cites the document it was taken from and applies only to the country named.

What it is used for

• Depression, which the NHS gives as the main reason it is prescribed
• Sometimes obsessive compulsive disorder (OCD) and anxiety

How it works in the body

The NHS says mirtazapine works by increasing the amount of two mood-related chemicals in the brain, noradrenaline and serotonin. Pharmacology reviews describe it as blocking alpha-2 receptors on nerve cells, which increases noradrenaline and serotonin release, and as also blocking 5-HT2 and 5-HT3 serotonin receptors. Blocking histamine H1 receptors is linked to its sedating effect. Unlike many antidepressants, it is described as not inhibiting the reuptake of noradrenaline or serotonin.

Cautions and interactions

• The NHS says mirtazapine is not usually recommended for anyone under 18.
• The NHS says it may be unsuitable for people with liver, kidney or heart disease, epilepsy, diabetes or schizophrenia, or who have had an allergic reaction or serious side effect with it before.
• The NHS says St John's wort should not be taken during treatment because it increases the risk of side effects.
• The NHS says mirtazapine can affect warfarin, so the dose of warfarin may need to change.
• The NHS says carbamazepine, phenytoin and rifampicin can reduce the effect of mirtazapine, so a higher dose may be prescribed.
• The NHS lists opioids such as morphine and medicines containing buprenorphine among the medicines to check before combining with mirtazapine.
• The NHS lists methadone, stimulants such as MDMA and cocaine, and hallucinogens such as LSD as combinations that can be dangerous, and says cannabis can make a person very sleepy.
• The NHS says alcohol can increase the risk of side effects such as feeling very drowsy.
• The NHS says there is no good evidence that mirtazapine taken in early pregnancy affects a baby's development, and that taking it late in pregnancy may slightly raise the risk of bleeding after delivery.
• The NHS says mirtazapine can be taken while breastfeeding if the baby is healthy, because it passes into breast milk in small amounts.
• The NHS says there is no clear evidence that mirtazapine affects fertility in men or women.
• The NHS says stopping suddenly can cause withdrawal symptoms, and a doctor will probably recommend reducing the dose gradually.

Interactions

Interactions documented in the official sources cited on each card. The list covers the medicines represented on this site and is not exhaustive; how the interaction data is compiled.

No pair records for this medicine are in the sources currently represented by Anatomy Nexus. Absence from this list does not mean no interaction exists.

Same-class and related medicines

Related medicines

Medicines often discussed alongside Mirtazapine: used together, compared with it, or acting on the same problem by a different route.

Key facts

What is mirtazapine used for?

Mirtazapine is an antidepressant. The NHS says it is prescribed mainly for depression, and sometimes for obsessive compulsive disorder (OCD) and anxiety. UK product information shows it as tablets, as tablets that melt on the tongue, and as an oral solution.

The NHS says mirtazapine is not usually recommended for anyone under 18. It says it is not a sleeping tablet, but it can make people feel sleepy, which may help people with depression who struggle to sleep.

The NHS groups antidepressants into types such as SSRIs, SNRIs, tricyclics and MAOIs, and lists mirtazapine as a noradrenaline and specific serotonergic antidepressant, or NaSSA. The NHS says an improvement in symptoms may be seen after a week, although it usually takes 4 to 6 weeks to feel the full benefits. A prescriber is the person to talk to about whether this medicine suits someone.

How does mirtazapine work?

The NHS says mirtazapine works by increasing the amount of two mood-related chemicals in the brain, noradrenaline and serotonin. Pharmacology reviews describe it as blocking alpha-2 receptors on nerve cells, which increases the release of noradrenaline and, through further receptors, serotonin. They add that it also blocks 5-HT2 and 5-HT3 serotonin receptors, which is linked to its calming and anti-sickness effects.

This pattern is why mirtazapine is called a noradrenergic and specific serotonergic antidepressant, or NaSSA. Unlike many other antidepressants, it is described as not inhibiting the reuptake of noradrenaline or serotonin.

Blocking histamine H1 receptors is linked to its sedating effect and to increased appetite. The NHS says mirtazapine is not a sleeping tablet but can make people feel sleepy. Because of this, the NHS advises against driving or using machinery until a person feels fully alert.

What are the side effects of mirtazapine?

The NHS lists feeling drowsy or sleepy, headaches and a dry mouth as common side effects. Increased appetite and weight gain, dizziness or shakiness, feeling or being sick, and diarrhoea are also listed. The NHS says these are usually mild and go away after a couple of weeks. For dry mouth, it suggests sugar-free gum or sweets.

Serious side effects are rare. The NHS lists allergic reaction, thoughts of suicide or self-harm, mania, liver problems and signs of infection from blood cell problems. The NHS describes the signs of infection as a high temperature, sore throat and mouth ulcers, and advises calling NHS 111 or a doctor. UK leaflets advise a prompt blood test if these signs appear.

The NHS side effects page says to call 999 or go to A&E now if a person has thoughts of harming themselves or ending their life, while the main NHS page says to call NHS 111. NHS 111 has a mental health option, and Samaritans can be reached free on 116 123 at any time.

Taking mirtazapine with other medicines, alcohol or drugs

The NHS says St John's wort should not be taken during treatment because it increases the risk of side effects. It says mirtazapine can affect warfarin, so the dose of warfarin may need to change. It says carbamazepine, phenytoin and rifampicin can reduce the effect of mirtazapine. It also lists opioids such as morphine and medicines containing buprenorphine among those to check before combining.

The NHS says alcohol can increase the risk of side effects such as feeling very drowsy. It lists methadone, stimulants such as MDMA and cocaine, and hallucinogens such as LSD as combinations that can be dangerous, and says cannabis can make a person very sleepy. It adds that mirtazapine has not been properly tested with recreational drugs.

A manufacturer's UK leaflet says mirtazapine, alone or combined with certain other medicines, can lead to serotonin syndrome, with signs such as unexplained fever, sweating, a faster heartbeat, diarrhoea and muscle contractions. MedlinePlus, a US source, advises calling a doctor right away for fever, sweating, confusion or a fast or irregular heartbeat.

Who needs extra care, and what about stopping?

The NHS says mirtazapine may be unsuitable for people with liver, kidney or heart disease, epilepsy, diabetes or schizophrenia. It may also be unsuitable for people who have had an allergic reaction or serious side effect with it before.

The NHS says there is no good evidence that taking mirtazapine in early pregnancy affects a baby's development, and that taking it late in pregnancy may slightly raise the risk of bleeding after delivery. It says mirtazapine can be taken while breastfeeding if the baby is healthy, because it passes into breast milk in small amounts. It also says there is no clear evidence that mirtazapine affects fertility in men or women.

The NHS advises against stopping an antidepressant suddenly, because it can cause withdrawal symptoms. A doctor will probably recommend reducing the dose gradually. The NHS says that for a mental health crisis, 999 is the route if someone is in immediate danger, and NHS 111 has a mental health option.

Frequently asked questions