Mirtazapine is a prescription antidepressant used mainly to treat major depressive disorder in adults. It belongs to a group of medicines called noradrenergic and specific serotonergic antidepressants, often shortened to NaSSAs.
Unlike some commonly prescribed antidepressants, mirtazapine can have a noticeable sedating effect, especially when treatment begins. It can also increase appetite, which is an important consideration when choosing an antidepressant. The medicine is usually taken once a day, often in the evening before sleep.
Mirtazapine has been available in the United States since 1996 and is sold as a generic medicine. It was also marketed under the brand name Remeron.
This guide explains what mirtazapine is, how it works, what it is used for, how it is taken, common side effects, important warnings, drug interactions, and what to know before starting or stopping treatment.
Quick Safety
- Take mirtazapine exactly as prescribed and do not change the dose or stop it suddenly without medical advice.
- It can cause drowsiness, dizziness, increased appetite, and weight gain, especially when you first start taking it.
- Avoid or limit alcohol because it can increase drowsiness.
- Tell your doctor about all medicines and supplements you take, especially other antidepressants or MAOIs.
- Contact your doctor if you develop severe mood changes, suicidal thoughts, unusual agitation, signs of infection, seizures, or symptoms of an allergic reaction.
- Mirtazapine may trigger mania in people with bipolar disorder, so tell your doctor about any history of manic or hypomanic episodes.
- If you take too much, seek urgent medical advice rather than waiting for symptoms to appear.
What Is Mirtazapine Used For?
The main approved use of mirtazapine is the treatment of major depressive disorder (MDD) in adults.
Depression can affect mood, sleep, appetite, concentration, energy, and interest in everyday activities. Doctors may prescribe mirtazapine when they believe an antidepressant is appropriate.
Mirtazapine may be particularly useful when depression occurs alongside problems such as poor sleep or reduced appetite. Its sedating and appetite-increasing effects can be helpful for some people, although those same effects can be unwanted for others.
Doctors sometimes prescribe mirtazapine for conditions other than its main approved use. These are called off-label uses. Such treatment decisions depend on the individual and should be made by a healthcare professional.
How Does Mirtazapine Work?
Mirtazapine works differently from many antidepressants such as selective serotonin reuptake inhibitors, or SSRIs.
It affects several chemical signaling systems in the brain, including serotonin and noradrenaline. In simple terms, mirtazapine changes the activity of certain receptors involved in these neurotransmitter systems.
This is one reason its effects can feel different from those of an SSRI.
The exact relationship between its receptor effects and improvement in depression is more complicated than simply saying that it “raises serotonin.” The medicine’s antidepressant effects develop over time rather than immediately after taking a tablet.
Mirtazapine also blocks certain histamine receptors. This contributes to its sedating effect and can explain why many people feel sleepy after taking it.
How Long Does Mirtazapine Take to Work?
Mirtazapine does not usually relieve depression immediately.
Some people notice changes in sleep, appetite, or anxiety relatively early in treatment. The antidepressant effect generally takes longer to develop. The NHS notes that mirtazapine often starts working after about one to two weeks, while the full benefit may take several weeks or longer.
If you have been taking it for several weeks without improvement, speak with your doctor rather than changing the dose yourself.
Antidepressant treatment also needs to be assessed over time. A medicine that does not seem helpful during the first few days may still have a therapeutic effect later.
How Is Mirtazapine Taken?
Mirtazapine is available in different forms, including regular tablets and orally disintegrating tablets. Some formulations are also available as an oral solution.
For adults, the usual starting dose in the U.S. prescribing information is 15 mg once daily, generally taken in the evening before sleep. Depending on the response and tolerability, a doctor may increase the dose, with a maximum recommended dose of 45 mg once daily in the U.S. labeling. Dose increases should not normally happen more often than every one to two weeks.
The exact dose prescribed to you may be different because doctors consider factors such as age, other medicines, kidney function, liver function, and how you respond to treatment.
Take mirtazapine exactly as prescribed. Do not increase the dose because you feel it is not working quickly enough.
Why Is Mirtazapine Usually Taken at Night?
Mirtazapine is commonly taken before bedtime because it can cause sleepiness.
This effect may be noticeable when you first start taking the medicine. Some people find it helpful when depression is accompanied by difficulty sleeping. Others may find daytime drowsiness inconvenient.
If mirtazapine makes you sleepy or affects your concentration, avoid driving, cycling, or operating machinery until you know how the medicine affects you.
The timing of the dose should follow your doctor’s instructions, particularly if your doctor has prescribed more than one dose per day.
Common Side Effects of Mirtazapine
Side effects vary from person to person. Many are more noticeable when treatment begins and may become less troublesome as the body adjusts.
Common side effects include:
- Sleepiness or drowsiness
- Increased appetite
- Weight gain
- Dizziness
- Headache
- Dry mouth
- Nausea
- Vomiting
- Diarrhea
- Shakiness or tremor
Sleepiness, increased appetite, and weight gain are among the side effects particularly associated with mirtazapine.
If a side effect is mild but continues to bother you, tell your doctor or pharmacist. You may not need to stop the medicine, but your treatment may need to be reviewed.
Mirtazapine and Weight Gain
Weight gain is one of the more commonly discussed effects of mirtazapine.
The medicine can increase appetite, and some people notice that they eat more after starting treatment. The change can be useful for someone who has lost their appetite during depression, but it may be frustrating for someone who is already concerned about their weight.
If your appetite changes significantly or your weight increases quickly, mention it to your healthcare professional. They can help you decide whether changes to diet, activity, monitoring, or treatment are appropriate.
Do not stop mirtazapine suddenly simply because you gain weight. There may be other treatment options, but the decision should be made with your prescriber.
Mirtazapine and Sleep
Mirtazapine can make people sleepy, particularly early in treatment. This is one of the reasons doctors commonly prescribe it in the evening.
For someone with depression and significant trouble sleeping, this effect may be useful. However, sedation can also become a problem if it continues into the daytime.
It is important not to assume that taking more mirtazapine will necessarily produce better sleep or better depression treatment. Use only the dose prescribed for you.
Serious Side Effects
Most people do not experience serious complications, but some reactions require prompt medical attention.
Seek medical help if you develop symptoms such as:
- Severe allergic reaction
- Seizures
- Chest pain or a fast or irregular heartbeat
- Unusual bruising or bleeding
- Signs of infection such as fever, sore throat, chills, or mouth sores
- Severe confusion, agitation, sweating, muscle stiffness, or unusual movements
- Symptoms of liver problems, including yellowing of the skin or whites of the eyes
- Severe eye pain or sudden changes in vision
Rare blood problems can occur with mirtazapine. Symptoms such as fever, chills, sore throat, or mouth sores can be signs of infection and should be assessed by a healthcare professional.
Suicidal Thoughts and Mood Changes
Like other antidepressants, mirtazapine carries a warning about an increased risk of suicidal thoughts and behaviors in children, teenagers, and young adults, particularly during the early stages of treatment or after a dose change. Mirtazapine tablets are not approved for pediatric patients in the U.S.
Anyone taking an antidepressant should also pay attention to major changes in mood or behavior.
Contact a healthcare professional promptly if you develop new or worsening depression, thoughts of self-harm, unusual agitation, severe restlessness, panic attacks, aggressive behavior, or unusually elevated or energized behavior.
If you are in immediate danger or think you may act on thoughts of harming yourself, seek emergency help immediately.
Mirtazapine and Bipolar Disorder
Depression can sometimes be part of bipolar disorder rather than major depressive disorder alone.
Before starting mirtazapine, doctors may screen for a history of bipolar disorder or manic episodes. Antidepressants can sometimes trigger mania or hypomania in susceptible people.
Tell your doctor if you have ever experienced periods of unusually high energy, very little need for sleep, racing thoughts, unusually rapid speech, impulsive behavior, or a significantly elevated or irritable mood.
Mirtazapine and Serotonin Syndrome
Mirtazapine can contribute to serotonin syndrome, particularly when combined with other medicines that increase serotonin activity.
Serotonin syndrome is uncommon but can be serious. Symptoms can include agitation, confusion, sweating, fever, rapid heartbeat, muscle stiffness or twitching, loss of coordination, nausea, vomiting, and diarrhea.
The risk is especially important when medicines affecting serotonin are combined. Tell your doctor and pharmacist about all antidepressants, prescription medicines, over-the-counter medicines, supplements, and herbal products you use.
Mirtazapine Drug Interactions
Mirtazapine can interact with other medicines.
One of the most important interactions involves monoamine oxidase inhibitors (MAOIs). Mirtazapine should not be taken with an MAOI or within 14 days of stopping one. Similarly, an MAOI should not generally be started until the appropriate interval has passed after stopping mirtazapine.
Other medicines can also affect mirtazapine or increase certain side effects. These include some antidepressants, opioids, benzodiazepines, epilepsy medicines, and other medicines that cause drowsiness. St. John’s wort can also interact with antidepressants and should not be started while taking mirtazapine without medical advice.
Always provide your doctor or pharmacist with a complete list of medicines and supplements you take.
Mirtazapine and Alcohol
Alcohol can increase the sedating effects of mirtazapine.
You may feel more sleepy, dizzy, or less alert when the two are combined. For this reason, the NHS advises avoiding alcohol while taking mirtazapine.
If you drink alcohol regularly, discuss this with your doctor rather than assuming that a small amount is safe for you.
Who Should Be Careful With Mirtazapine?
Mirtazapine is not suitable for everyone.
Tell your doctor before starting it if you have or have had:
- Kidney disease
- Liver disease
- Heart disease
- Epilepsy or seizures
- Diabetes
- Low blood pressure
- High cholesterol or triglycerides
- Glaucoma
- Bipolar disorder
- A previous allergic reaction to mirtazapine
Your doctor may need to adjust the dose or monitor you more closely in some of these situations. People with moderate to severe kidney or liver impairment may require dose adjustments.
Older adults may also need additional monitoring because medicines can affect them differently.
Mirtazapine During Pregnancy and Breastfeeding
If you are pregnant, planning a pregnancy, or breastfeeding, tell your doctor before taking mirtazapine.
Pregnancy does not automatically mean that mirtazapine must be stopped. The decision involves weighing the benefits of treating depression against possible risks to the mother and baby.
Mirtazapine can sometimes be used while breastfeeding because only small amounts pass into breast milk, but your healthcare professional should assess the individual situation.
Do not stop an antidepressant suddenly because you discover that you are pregnant. Speak with your doctor first.
What Happens If You Miss a Dose of Mirtazapine?
If you take mirtazapine once a day and forget a dose, follow the instructions provided by your doctor or medication leaflet.
The NHS advises people taking it once daily to skip the missed dose and take the next dose at the usual time. Do not take two doses to make up for the missed one.
If your doctor has prescribed mirtazapine twice a day, the instructions can be different.
What Happens If You Take Too Much Mirtazapine?
Taking more mirtazapine than prescribed can be dangerous.
An overdose may cause excessive sleepiness and other symptoms. If you think you have taken too much, seek urgent medical advice or contact your local poison control service. If someone collapses, has a seizure, has trouble breathing, or cannot be awakened, emergency medical care is needed immediately.
Do not wait for symptoms to become severe before seeking advice.
Stopping Mirtazapine
Mirtazapine should not normally be stopped suddenly.
Stopping an antidepressant abruptly can cause withdrawal or discontinuation symptoms. These can include dizziness, anxiety, nausea, sleep problems, headaches, and unusual sensations.
Your doctor can gradually reduce the dose to make stopping easier. The NHS specifically advises speaking with your doctor before stopping mirtazapine and notes that the dose may be reduced over several weeks or months.
How quickly the dose should be reduced depends on the person, the dose, how long they have taken the medicine, and their previous experience with stopping antidepressants.
Is Mirtazapine Addictive?
Mirtazapine is not considered addictive in the same way as substances such as nicotine or certain recreational drugs.
However, your body can adapt to the medicine. This is one reason stopping suddenly can cause discontinuation symptoms.
Needing to reduce the dose gradually does not mean that the medicine is addictive. It means that the nervous system may need time to adjust as treatment ends.
Mirtazapine Compared With Other Antidepressants
There are several types of antidepressants, and they do not affect everyone in exactly the same way.
SSRIs are often used as a first treatment for depression. Mirtazapine works through a different mechanism and has its own pattern of benefits and side effects.
One practical difference is sedation. Mirtazapine can be useful for someone whose depression is accompanied by poor sleep, but it may be less attractive for someone who needs to remain highly alert during the day.
Another difference is appetite. Increased appetite and weight gain are recognized effects of mirtazapine, so this needs to be considered when choosing treatment.
There is no universally “best” antidepressant. The right choice depends on symptoms, medical history, previous treatment, other medicines, side effects, and personal circumstances.
What to Expect When Starting Mirtazapine
The first few days can feel different from the weeks that follow.
You may notice sleepiness, increased appetite, dizziness, or other side effects before you notice a clear improvement in depression.
The medicine generally needs time to work. The NHS says mirtazapine often begins working after one to two weeks, with further improvement developing over the following weeks.
Keep track of changes in mood, sleep, appetite, energy, and side effects. This information can make follow-up appointments more useful.
If symptoms become worse, especially if you develop suicidal thoughts or severe behavioral changes, contact your healthcare professional promptly.
How Long Do People Take Mirtazapine?
The length of treatment varies.
Doctors generally continue antidepressant treatment after depression improves to reduce the chance of symptoms returning. The NHS notes that antidepressants are commonly continued for at least four to six months after symptoms have improved, although treatment may last much longer for some people.
The decision to continue or stop mirtazapine depends on your history and response to treatment.
It is not a medicine that should be stopped simply because you feel better. Feeling better may be a sign that treatment is working.
How Should Mirtazapine Be Stored?
Keep mirtazapine in its original container and away from excessive heat and moisture.
Keep it out of sight and reach of children. Unused medicine should be disposed of safely rather than shared with another person or flushed down the toilet. A pharmacist or local medicine take-back program can provide disposal guidance.
Frequently Asked Questions
Can mirtazapine affect your dreams?
Yes. Some people notice more vivid or unusual dreams while taking mirtazapine. Changes in sleep patterns can also make dreams easier to remember.
Can mirtazapine cause constipation?
It can, although constipation is not among the most common side effects. Drinking enough water and getting enough fiber may help. Persistent constipation should be discussed with a healthcare professional.
Can mirtazapine cause headaches?
Yes, headaches can occur while taking mirtazapine. They may become less noticeable as your body adjusts to the medicine. Severe or persistent headaches should be discussed with your doctor.
Can mirtazapine affect cholesterol levels?
Mirtazapine may cause changes in cholesterol or triglyceride levels in some people. Your doctor may recommend blood tests if you have certain risk factors or use the medicine for a long period.
Does mirtazapine affect blood sugar?
It can affect blood sugar indirectly through changes in appetite and weight. People with diabetes should follow their healthcare professional’s advice about monitoring blood glucose while taking mirtazapine.
Can mirtazapine cause restless legs?
Unusual movement-related symptoms can occur with medicines that affect the nervous system, although restless legs is not a common effect of mirtazapine. Tell your doctor if you develop persistent or uncomfortable sensations in your legs.
Does mirtazapine affect blood pressure?
Mirtazapine can sometimes cause low blood pressure, particularly when standing up. This may lead to dizziness or lightheadedness. If this happens frequently, talk with your doctor.
Can you take mirtazapine with painkillers?
It depends on the specific painkiller. Some medicines, particularly certain opioids, can increase drowsiness and other risks when combined with mirtazapine. Check with a doctor or pharmacist before taking them together.
Can mirtazapine change your appetite after you stop taking it?
Appetite changes related to mirtazapine may improve after stopping the medicine, but the timing varies. Appetite can also be affected by diet, activity, and the condition being treated.
Does mirtazapine work differently at different doses?
Yes, its effects can vary depending on the dose and the individual. A higher dose does not necessarily mean better results or less drowsiness. Dose changes should only be made under medical guidance.
Conclusion
Mirtazapine is a prescription antidepressant primarily used to treat major depressive disorder in adults. It works differently from SSRIs and affects serotonin and noradrenaline signaling in the brain.
Its most noticeable characteristics are that it can cause sleepiness and increased appetite, particularly when treatment begins. For some people, these effects may be useful when depression is accompanied by poor sleep or low appetite. For others, they can be unwanted.
The usual U.S. starting dose is 15 mg once daily, generally taken in the evening, and the maximum recommended dose is 45 mg per day. The dose should be determined and adjusted by a healthcare professional.
Like every prescription medicine, mirtazapine has potential risks and interactions. Important considerations include suicidal thoughts and behavior in younger patients, serotonin syndrome, rare blood problems, allergic reactions, mania, seizures, and interactions with other medicines.
Most importantly, mirtazapine should be taken exactly as prescribed and should not be stopped suddenly without medical guidance. If you are considering starting, changing, or stopping the medicine, talk with your doctor or pharmacist about what is appropriate for you.
Disclaimer – This guide is for general educational purposes and is not a substitute for medical advice, diagnosis, or treatment. Always follow the prescribing information provided with your medicine and advice from your healthcare professional.
