Mirtazapine is a prescription antidepressant used to treat major depressive disorder in adults. It belongs to a group of medicines that works differently from many commonly used antidepressants. It is also known for causing sleepiness and increasing appetite in some people, which can be helpful or unwanted depending on the individual.
Like any prescription medicine, mirtazapine can cause side effects. Some are mild and may improve as your body adjusts to the medicine. Others are less common but can require prompt medical attention.
Knowing what to expect can help you recognize which symptoms may be related to mirtazapine and when it is important to contact a healthcare professional.
Quick Safety
- Mirtazapine can cause side effects, but not everyone who takes it will experience them.
- Sleepiness, increased appetite, weight gain, dizziness, dry mouth, and constipation are among the commonly reported side effects.
- Some side effects may become less noticeable as the body adjusts to the medicine, but persistent problems should be discussed with a healthcare professional.
- Mirtazapine can cause serious reactions in rare cases, so symptoms such as seizures, severe allergic reactions, or signs of serotonin syndrome require prompt medical attention.
- Do not stop mirtazapine suddenly without speaking with your healthcare provider, as discontinuation symptoms can occur.
What Are the Most Common Side Effects of Mirtazapine?
The most common side effects reported with mirtazapine include sleepiness, increased appetite, weight gain, dizziness, dry mouth, constipation, and abnormal dreams.
Not everyone taking mirtazapine will experience these effects. The severity can also vary from person to person.
Some side effects may be more noticeable when you first start treatment. If a side effect is bothersome or does not improve, speak with your doctor or pharmacist rather than stopping the medication on your own.
1. Sleepiness
Sleepiness is one of the most commonly reported effects of mirtazapine.
The medicine can make some people feel very tired or sleepy, particularly when they first begin taking it. This is one reason mirtazapine is commonly taken in the evening.
The prescribing information warns that mirtazapine can affect judgment, thinking, and motor skills. You should understand how the medicine affects you before driving or operating machinery.
If you continue to feel excessively sleepy during the day, tell your healthcare provider. They may want to review your dose, other medicines, or your overall treatment plan.
2. Increased Appetite
Mirtazapine can increase appetite.
Some people may feel hungrier than usual after starting treatment or may notice that they are eating more frequently. Increased appetite is a recognized side effect of the medicine.
For someone who has struggled with poor appetite while depressed, this effect may not necessarily be unwanted. However, increased appetite can become a concern if it leads to unwanted weight gain.
If you notice a significant change in your appetite, discuss it with your healthcare professional.
3. Weight Gain
Weight gain is another commonly reported side effect.
In clinical trials cited in the prescribing information, 12% of people receiving mirtazapine experienced weight gain compared with 2% receiving placebo. Increased appetite was also reported more often with mirtazapine.
Weight changes can happen for different reasons. Increased appetite is one possible contributor, while changes in eating patterns and activity can also play a role.
If you are concerned about gaining weight while taking mirtazapine, talk with your healthcare provider. They can help you determine whether the change may be related to the medication and discuss appropriate options.
4. Dizziness
Dizziness can occur while taking mirtazapine.
You may feel lightheaded or unsteady, particularly when getting up or moving around. In clinical trials, dizziness occurred more often in people taking mirtazapine than those receiving placebo.
If you feel dizzy, take care when standing or walking until you know how the medicine affects you.
Persistent or severe dizziness should be discussed with your healthcare provider.
5. Dry Mouth
Some people taking mirtazapine experience dry mouth.
Dry mouth can be uncomfortable and may make it harder to speak, swallow, or eat normally. It can also contribute to dental problems if it continues for a long time.
Drinking water regularly and maintaining good oral hygiene may help. If dry mouth is persistent or severe, ask your healthcare professional or dentist about ways to manage it.
6. Constipation
Constipation is another possible side effect of mirtazapine. It is listed among the common side effects in the medication guide.
You may notice fewer bowel movements, harder stools, or difficulty passing stool.
Drinking enough fluids, eating fiber-rich foods, and staying physically active may help some people. However, if constipation becomes severe or continues, talk with a healthcare professional before taking a laxative or other treatment.
7. Abnormal Dreams
Some people report unusual or abnormal dreams while taking mirtazapine. This is also listed among the common possible side effects.
The dreams may simply be more vivid or different from what you normally experience.
If unusual dreams are interfering with your sleep or causing significant distress, mention them to your healthcare provider.
8. Changes in Cholesterol and Triglycerides
Mirtazapine has been associated with increases in cholesterol and triglyceride levels in some patients.
You may not notice any symptoms when these blood levels change. Your healthcare provider may decide that blood tests are appropriate depending on your health history and other risk factors.
If you already have high cholesterol or triglycerides, make sure your doctor knows before and during treatment.
9. Low Sodium Levels
Mirtazapine can cause hyponatremia, which means a lower-than-normal sodium level in the blood. This can be serious in some cases.
Possible symptoms can include headache, difficulty concentrating, memory changes, confusion, weakness, and unsteadiness.
Older adults may have a higher risk.
Severe or sudden symptoms require prompt medical attention.
10. Changes in Liver Function
Mirtazapine has been associated with elevations in liver enzymes, and clinically significant elevations have occurred. The prescribing information recommends caution in people with impaired liver function.
Most people will not develop a serious liver problem, but tell your healthcare provider if you have a history of liver disease.
Unexplained symptoms such as yellowing of the skin or eyes, dark urine, or significant changes in health should be evaluated promptly.
Serious Side Effects of Mirtazapine
Most people do not experience serious complications, but mirtazapine has several important warnings.
Suicidal Thoughts or Behaviors
Like other antidepressants, mirtazapine carries a boxed warning about an increased risk of suicidal thoughts and behaviors in some children, adolescents, and young adults, particularly during the early stages of treatment or when the dose changes. Mirtazapine is not approved for use in children.
Sudden changes in mood, behavior, thoughts, or feelings should be taken seriously.
Anyone experiencing thoughts of suicide or self-harm should seek immediate professional or emergency help.
Serotonin Syndrome
Serotonin syndrome is a potentially serious condition that can occur when medicines affecting serotonin are combined or, less commonly, with mirtazapine alone.
Symptoms can include agitation, hallucinations, changes in mental status, muscle twitching or coordination problems, sweating, fever, rapid heartbeat, changes in blood pressure, nausea, vomiting, or diarrhea.
The risk can be higher when mirtazapine is taken with certain other medicines that affect serotonin.
Seek urgent medical attention if you develop symptoms that could indicate serotonin syndrome.
Low White Blood Cell Count
Mirtazapine can rarely cause a significant decrease in white blood cells called agranulocytosis. White blood cells help the body fight infections.
Warning signs can include fever, chills, sore throat, mouth or nose sores, or flu-like symptoms.
Contact your healthcare provider promptly if these symptoms occur while taking mirtazapine.
Mania or Hypomania
Mirtazapine can trigger mania or hypomania in some people, particularly those with bipolar disorder.
Warning signs can include unusually high energy, very little need for sleep, racing thoughts, unusually fast talking, excessive happiness or irritability, reckless behavior, or unusually grand ideas.
Tell your doctor if you have a personal or family history of bipolar disorder before starting an antidepressant.
Seizures
Seizures are another uncommon but serious potential adverse effect. The prescribing information recommends caution when mirtazapine is used in people with a seizure disorder.
If someone experiences a seizure, emergency medical care is needed.
Severe Allergic Reactions
As with other medicines, a serious allergic reaction is possible.
Seek emergency medical care for symptoms such as difficulty breathing, severe swelling, or other signs of a serious allergic reaction.
Can Mirtazapine Cause Sexual Side Effects?
Sexual side effects can occur with antidepressants, although mirtazapine’s overall side-effect profile differs from that of many serotonin reuptake inhibitor antidepressants.
If you notice changes in sexual desire, arousal, or sexual function after starting mirtazapine, discuss them with your healthcare provider.
Do not stop the medicine without medical advice simply because of a side effect. Your healthcare provider can discuss whether the symptom may be related to mirtazapine and what options are available.
Does Mirtazapine Make You Sleepy During the Day?
It can.
Sleepiness is one of the most common adverse reactions reported with mirtazapine. In clinical trials, somnolence occurred in 54% of patients taking mirtazapine compared with 18% taking placebo.
The effect can be particularly noticeable when starting treatment.
Until you know how mirtazapine affects you, avoid driving, operating machinery, or doing activities that require full alertness.
Alcohol and certain sedating medicines can further increase drowsiness, so discuss alcohol and other medicines with your healthcare provider.
Does Mirtazapine Cause Weight Gain in Everyone?
No.
Although increased appetite and weight gain are among the more common side effects, not everyone taking mirtazapine will gain weight.
Clinical trial data showed weight gain occurred more frequently with mirtazapine than placebo, but individual responses vary.
If weight changes become a concern, speak with your healthcare provider rather than changing your medication or diet dramatically on your own.
Can You Stop Mirtazapine Suddenly?
Stopping mirtazapine suddenly can cause discontinuation symptoms. The prescribing information includes discontinuation syndrome among the warnings and precautions.
Possible symptoms can include nausea, dizziness, headache, anxiety, sleep problems, or other changes.
If you want to stop taking mirtazapine, talk with your healthcare provider. They can determine whether your dose should be reduced gradually.
When Should You Contact a Doctor?
Contact your healthcare provider if you develop side effects that are persistent, severe, or interfering with your daily activities.
You should seek urgent medical attention for symptoms such as:
- Suicidal thoughts or behavior
- Seizures
- Severe allergic reactions
- Signs of serotonin syndrome
- Severe confusion
- Fainting or serious heart-related symptoms
- High fever with signs of infection
- Severe changes in behavior or mood
These symptoms can have different causes, but they should not be ignored.
Frequently Asked Questions
How long do mirtazapine side effects usually last?
The duration varies from person to person. Some side effects may improve as your body adjusts to the medicine, while others may continue during treatment. Talk with your healthcare provider if a side effect does not improve.
Are mirtazapine side effects worse when you first start taking it?
Some side effects may be more noticeable during the early part of treatment. Your healthcare provider can advise you if symptoms are persistent or difficult to manage.
Does mirtazapine affect blood pressure?
Mirtazapine can affect blood pressure in some people, although significant blood pressure changes are not among its most common effects. Tell your doctor if you experience unusual dizziness, fainting, or other concerning symptoms.
Can mirtazapine cause headaches?
Headache can occur in people taking mirtazapine. If headaches are severe, persistent, or accompanied by other concerning symptoms, contact your healthcare provider.
Does mirtazapine cause nausea?
Nausea can occur with mirtazapine. If nausea is severe or does not improve, speak with your doctor or pharmacist.
Can mirtazapine cause swelling?
Swelling or edema has been reported with mirtazapine. New or unexplained swelling should be discussed with a healthcare professional, particularly if it is sudden or accompanied by breathing difficulties.
Does mirtazapine affect blood sugar?
Changes in appetite and weight can indirectly affect blood sugar control. People with diabetes should discuss significant changes in weight, eating patterns, or blood glucose levels with their healthcare provider.
Can mirtazapine cause hair loss?
Hair loss is not considered one of the most common effects of mirtazapine, but unusual symptoms should still be discussed with a healthcare professional if they appear after starting treatment.
Can mirtazapine cause restless legs?
Some people may experience unusual movement-related symptoms while taking medicines that affect the nervous system. If you develop persistent restlessness or an uncomfortable urge to move your legs, tell your healthcare provider.
Can mirtazapine affect your menstrual cycle?
Changes in menstruation are not among the most common effects of mirtazapine. If you notice an unexpected change in your menstrual cycle after starting the medicine, discuss it with your healthcare provider.
Conclusion
Mirtazapine can be an effective prescription treatment for major depressive disorder, but like other antidepressants, it can cause side effects.
The most common include sleepiness, increased appetite, weight gain, dizziness, dry mouth, constipation, and abnormal dreams.
Some less common reactions can be more serious, including low sodium levels, low white blood cell counts, serotonin syndrome, seizures, changes in liver function, and activation of mania or hypomania.
Not everyone will experience side effects, and the effects can vary from person to person. If you have started mirtazapine and notice a symptom that concerns you, talk with your doctor or pharmacist. Do not change your dose or stop taking the medicine without professional guidance.
Disclaimer: This article is for general educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always follow your prescription instructions and speak with a qualified healthcare professional about side effects or concerns related to mirtazapine.
