Mirtazapine belongs to the group of medications known as tetracyclic antidepressants. Antidepressants are used to help relieve the symptoms of mental depression such as feeling low, sleeping problems, loss of appetite, and loss of interest in activities that you would normally enjoy doing.

When you have depression, certain chemicals in the brain are out of their normal balance. Antidepressants such as mirtazapine work by helping to bring the chemicals back into balance. Antidepressants usually take at least a few weeks for their beneficial effects to be noticed, so it is important to have patience and take the medication exactly as prescribed.

Your doctor may have suggested this medication for conditions other than the ones listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The recommended starting dose of mirtazapine for adults is 15 mg (one-half tablet) taken once daily in the evening before going to bed. The doctor may increase the dose to 30 mg after one to two weeks, depending on circumstances. The maximum recommended dose of mirtazapine is 45 mg daily.

It is very important to take this medication exactly as prescribed. It is normal not to feel any different for the first 2 to 4 weeks of taking this medication. If you have side effects from this medication, talk with your doctor or pharmacist before stopping it. If you forget a dose and remember the same day, take the missed dose as soon as possible. If you do not remember until the next day, skip the missed dose and go back to your regular dosing schedule. Do not take a double dose to make up for a missed one.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

Keep this and other medications out of reach of children. Store in a dry place at room temperature.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

Mirtazapine should not be used:

• by anyone allergic to any of the ingredients of the tablet
• within two weeks of taking MAO inhibitors (e.g., phenelzine, tranylcypromine)

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your health professional. They may be able to help you to deal with some of the effects.

The following side effects may go away as your body becomes used to the medication; check with your doctor if they continue or become bothersome.

More common
• constipation
• dizziness
• drowsiness
• dry mouth
• increased appetite
• sedation
• weight gain

Less common
• abdominal pain
• abnormal dreams
• back pain
• dizziness upon rising
• increased need to urinate
• increased sensitivity to touch
• increased thirst
• low blood pressure
• muscle pain
• nausea
• trembling
• vomiting
• weakness

Contact your doctor as soon as possible if the following side effects occur:

Less common
• agitation
• anxiety
• breathing problems
• increased or decreased movement
• mood changes (undesirable)
• rash
• swelling

Rare
• decreased sexual ability
• hallucinations (hearing, seeing, or feeling things that are not there)
• menstrual difficulties
• mood swings
• unusual excitement

Get immediate medical attention if any of the following side effects occur:

Rare
• mouth sores
• seizures
• sore throat, chills, and fever
• tremors

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Suicidal or agitated behaviour: Adults and children taking this medication may feel agitated (restless, anxious, aggressive, emotional, and feeling not like themselves), or they may want to hurt themselves or others. These symptoms may occur within several weeks after people start taking this medication. People taking this medication should be closely monitored by their doctor and caregivers for emotional and behavioural changes.

Drowsiness/reduced alertness: Mirtazapine may cause drowsiness. People taking this medication should avoid potentially dangerous activities such as driving a motor vehicle or operating machinery.

Medical conditions: Mirtazapine may worsen the following conditions:

• glaucoma
• heart disease
• high cholesterol
• low blood pressure (hypotension), especially low blood pressure upon standing up (orthostatic hypotension)
• enlarged prostate gland
• seizures
• urinary retention

As well, mirtazapine should be taken cautiously by people with:

• liver disease or kidney disease, as they may experience increased side effects;
• diabetes, as it may affect blood sugar; or
• mania, as it may cause worsening or a recurrence of mania symptoms.

Stopping the medication: Stopping this medication suddenly may lead to side effects. A gradual reduction in dose over a period of time is recommended. If you are thinking of stopping the medication, check with your doctor first.

Pregnancy: The safe use of mirtazapine during pregnancy has not been established. It has been reported that babies born to women who have taken mirtazapine during the last trimester of pregnancy may be adversely affected, resulting in complications that caused an increase in the length of hospital stay. Physicians and pregnant women should carefully consider the benefits and the risks of all treatment options.

Breast-feeding: It is not known whether mirtazapine passes into breast milk. Its use while nursing is not recommended.

Children and adolescents: The safety and effectiveness of this medication for children and adolescents younger than 18 years of age have not been established. There have been reports that the use of this medication by children and adolescents younger than 18 years may cause behavioural and emotional changes, such as suicidal thoughts and behaviour. Children and adolescents who take this medication should be closely monitored and encouraged to report all changes in feelings to their doctor and caregiver.

The following may interfere with the action of mirtazapine or may increase the risk of side effects:

• alcohol
• benzodiazepines (e.g., diazepam, lorazepam, oxazepam)
• MAO inhibitors (e.g., phenelzine, tranylcypromine). Mirtazapine should not be taken with these medications or within two weeks before or after taking them
• tricyclic antidepressants (e.g., amitriptyline, nortriptyline, doxepin, amoxapine)

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. In many cases, interactions are intended or are managed by close monitoring. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.