Mirtazapine: uses, side effects and bedtime dosing

The NHS describes mirtazapine as an antidepressant for treating depression. It raises levels of brain chemicals that affect mood, particularly serotonin, which can improve mood and reduce negative thoughts.

It is not recommended for under-18s.

Drowsiness is a recognised effect, so the NHS says it is usually taken once a day at bedtime. Some doctors split the dose between morning and evening. Mirtazapine is made as tablets you swallow, as dissolving tablets and as a liquid, so there is a choice if tablets are hard to swallow.

For some people the sleepy effect is helpful, especially when low mood has disturbed sleep. For others it carries into the day, and that is worth telling your prescriber about.

The NHS says mirtazapine usually starts working after one or two weeks, which is quicker than the several weeks quoted for many other antidepressants. Treatment normally continues for at least four to six months.

Because the sleepy effect often appears before the lift in mood, some people feel more tired for a few days before they notice any benefit. That pattern is one reason to keep taking it as prescribed and to report how you are doing at your first review, not to judge it on the first night. Keeping a simple note of sleep, appetite and mood helps the conversation with your prescriber.

If you miss a dose, leave it and take the next one on time. Do not double up.

Most common effects ease after about two weeks as the body adjusts. If they persist, speak to a pharmacist or doctor.

• Common: drowsiness, headaches, dry mouth, a bigger appetite and weight gain, dizziness, shakiness, nausea, vomiting and diarrhoea.

• Do not drive, cycle or use machinery if you feel drowsy or cannot concentrate.

• Call 999 for anaphylaxis: a swollen throat or tongue, a rash or difficulty breathing.

• Call NHS 111 for thoughts of self-harm, unusual energy or mania, yellowing of the skin or eyes (liver problems), or fever, sore throat and mouth ulcers (possible blood-cell problems).

The NHS says mirtazapine may be unsuitable if you are allergic to it or have liver, kidney or heart disease, epilepsy, diabetes or schizophrenia. Tell the prescriber about these before you start.

Combining mirtazapine with other sedating or mood-altering drugs can add to drowsiness or cause other problems. The NHS lists MAOIs, SSRIs, opioids and certain painkillers, epilepsy medicines and benzodiazepines, as well as St John's wort.

Alcohol increases drowsiness and other side effects, so the NHS says it is best not to drink.

The NHS says mirtazapine can be used in pregnancy if the benefits outweigh the risks. Only a minimal amount reaches breast milk, but alternatives may be considered, so talk to your doctor.

Never stop suddenly. A gradual reduction over weeks or months avoids withdrawal symptoms. Suspected side effects can be reported to the MHRA Yellow Card scheme.