Mirtazapine Side Effects

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As depression continues to grow as a problem, experts have been coming up with newer medications and modalities to fight it. Mirtazapine is of the medications commonly used to manage depressive symptoms, and millions of people swear by its benefits. However, no medication comes without side effects, and unfortunately, many have reported experiencing various mirtazapine side effects of varying nature and intensity. Understanding these side effects is essential for anyone using the medication to anticipate what they can experience in the future and when to call for help.

An Overview of Mirtazapine and How It Works

Mirtazapine is a prescription-based drug available in orally disintegrating and immediate-release tablets. It commonly comes as a brand name Remeron but many generic versions are also available at lesser costs. The medication belongs to a class of drugs called antidepressants. Experts prescribe it alone or in combination with other drugs to help people fight depressive symptoms. [1]

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So far, experts are unclear about the exact mechanism through which mirtazapine works to manage depression. However, some theories suggest that it boosts the levels of serotonin and norepinephrine in the brain to increase happiness and regulate mood positively.

Mirtazapine Side Effects: What to Expect

While the efficacy of mirtazapine is proven, the medication does not come without side effects. So far, it has been reported to cause drowsiness while impairing a user’s ability to think clearly, react quickly, or make decisions. Some people also report feeling increasingly agitated during the first few weeks of taking this medication; however, this side effect typically settles on its own with time.

Mentioned below is a list of mirtazapine side effects, including the most common ones and the rare serious ones.

Common Side Effects

Mirtazapine may commonly cause the following side effects in users:

  • Increased appetite
  • Dizziness
  • Sleepiness
  • Dry mouth
  • Weight gain [2]
  • Strange dreams
  • Constipation

For most people, the side effects mentioned above remain mild and usually go away within a few days to a few weeks. However, if they do not go away on their own, contact a doctor.

Serious Side Effects

Unfortunately, mirtazapine can sometimes cause serious side effects in certain users. Experts recommend keeping an eye on the side effects that appear and monitor them. If a person feels that these adverse effects are becoming life-threatening or turning into a medical emergency at any point, they must get medical help right away. Some potential dangers associated with mirtazapine use include the following:

  • Suicidal Thoughts: This may include attempts to take your own life, acting violent or aggressive, acting on dangerous impulses, developing new depression or worsening of the existing one, feeling agitated, angry, irritable, or restless, or other unusual mood changes.
  • Manic Episodes: Manic episodes can make a person feel highly energized, have racing thoughts, experience reckless behaviors, and have grand ideas. Mania due to mirtazapine can also make them excessively happy to the point that they struggle to sleep.
  • Poor immunity: Mirtazapine can reduce the white cell count. White cells are a type of blood cells that help the body fight infections. Once their levels go down, a person may repeatedly experience signs of infections, such as sore throat, chills, fever, sores in the nose or mouth, body aches, vomiting, and fatigue.
  • Serotonin Syndrome: This condition includes an overflow of serotonin in the brain which may prove life-threatening. Some symptoms of serotonin syndrome may include hallucinations, agitation, trouble thinking, fever, sweating, a racing heart, poor coordination, muscle twitching, nausea, vomiting, diarrhea, and changes in blood pressure.
  • Eye Problems: Using mirtazapine can make some people experience eye pain, swelling, or redness in the eyes, or changes in vision.
  • Seizures
  • Hyponatremia: This condition causes sodium levels to drop in the blood. This side effect is more common in the elderly population and may cause headaches, confusion, memory issues, poor concentration, and feeling weak or unsteady.
  • Severe Skin Reactions: The symptoms of a severe skin reaction include a skin rash associated with swelling. This rash usually occurs on the soles of feet or palms of hands. Some people may develop painful blisters or ulcers in the mouth or on the body.
  • Severe Allergic Reactions: A severe allergic reaction may make a person struggle to breathe, cause swelling in the face, eyes, or mouth, and the development of rashes or blisters.
  • Rhabdomyolysis: This side effect constitutes a severe muscle problem that may cause pains and aches in the muscles in addition to kidney problems.

Mirtazapine Interactions: Drugs That Increase Its Side Effects

While mirtazapine can cause many side effects on its own but using it with certain others. Medications may intensify these issues. These medications may include the following:

  • Benzodiazepines: These medications include triazolam, midazolam, and diazepam, and using them with mirtazapine can cause increased drowsiness and sedation.
  • Triptans: These medications, such as sumatriptan, can increase the risk of serotonin syndrome when used with mirtazapine. Hence, always ask your doctor about the safety of combining the two.
  • Lithium: Ask a doctor if you can take mirtazapine if you are already on lithium. The combination may heighten the risk of serotonin syndrome.
  • Warfarin: Using warfarin with mirtazapine may put a user at an increased risk of bleeding.
  • Drugs Affecting Heart Rhythm: Certain antibiotics and antipsychotics may alter the heart rhythm and may not be safe to use with mirtazapine. The combination of such drugs may lead to an issue called QT prolongation.
  • Serotongenic Medications: These medications, such as tramadol and fentanyl, may put a person at an increased risk of serotonin syndrome when used with mirtazapine.

Other medications to be cautious about while using mirtazapine include the following:

  • Cimetidine
  • Antibiotics, for example, erythromycin
  • Antifungals, for example, ketoconazole
  • Protease inhibitors drugs, such as ritonavir
  • Carbamazepine
  • Phenytoin

Mirtazapine Warnings: What To Remember to Minimize Side Effects

People who are planning to use mirtazapine must keep the following warnings in mind to ensure that their risk of experiencing side effects remains minimal.

Suicide warning

Mirtazapine comes with a black box warning, the most serious warning issued by the Food and Drug Administration (FDA), which alerts patients and doctors about potentially dangerous side effects of a drug. In the case of mirtazapine, the drug can cause people to become suicidal. The risk is particularly higher in teenagers and young adults, and most users are vulnerable to this warning during the first few months of beginning treatment. People starting treatment with mirtazapine must alert their loved ones and the doctor to keep an eye on any changes in their behavior, feelings, thoughts, or mood and alert the medical authorities right away in case a suidicalal tendency is spotted.

Withdrawal warning

Experts strictly advise against stopping mirtazapine without seeking advice from a professional. Sudden cessation of this drug can lead to withdrawal side effects, such as shakiness, agitation, electric shock-like feelings, and anxiety. Some people may also experience vomiting, nausea, tiredness, dizziness, headache, confusion, and strange dreams. If you wish to stop using this drug, a doctor may make a tapering schedule that allows you to gradually reduce the dosage and discontinue the drug over time while minimizing the risk of a withdrawal.

Drowsiness warning

Mirtazapine can commonly cause drowsiness in its users. Additionally, it may impair their ability to make decisions, respond quickly, and think clearly. Hence, people who have started using it only recently must not use machinery, drive, or engage in any activities that require precision or alertness as doing so may put them in harm.

Warning for increased appetite and weight gain

Mirtazapine can make people feel hungrier than usual, eventually leading to weight gain. If this side effect is a concern for you, talk to a doctor regarding possible alternatives.

Warning for people with seizures

People with a history of seizures must talk to a doctor if using mirtazapine is safe for them as the drug can make their condition work. If using this drug triggers a seizure, the doctor may advise them to stop or lower its dose.

Warning for people with heart problems

If you have a history of cardiovascular issues, talk to a doctor if taking mirtazapine is safe for you. [3] This is particularly important for people with a history of stroke, heart attack, or angina. Because mirtazapine can cause a drop in blood pressure, it may worsen any pre-existing heart issues.

Warning for people with eye problems

Mirtazapine can dilate pupils, which may trigger a glaucoma attack in people with a pre-existing disease.

Warning for people with kidney issues

Kidneys are primarily responsible for clearing mirtazapine from the system. Those with pre-existing renal issues may not be able to get rid of the drug from their body, causing it to build up. As the levels of mirtazapine increase, its side effects may intensify.

Warning for people with liver problems

People with ongoing liver issues or a history of liver disease may not be able to break down mirtazapine as effectively as others. Consequently, the drug may start accumulating in the body, exacerbating the side effects.


Will mirtazapine side effects affect my ability to take tests and exams?

Because of the unpredictability of side effects, experts usually recommend not starting mirtazapine for the first time close to exams. The medication may make users feel dizzy, tired, or less alert, which may interfere with their ability to prepare for and take exams.

Is it safe to take mirtazapine if I am pregnant?

Research so far has proven that taking mirtazapine during the first trimester does not cause any issues in the baby. It has not led to any malformations in pregnant women as long as they use it as prescribed. Some studies suggest that it may slightly increase the risk of a miscarriage or preterm birth. A theory suggests that women who take mirtazapine after the 20th week of pregnancy may put their baby at risk of persistent pulmonary hypertension in the newborn (PPHN), a condition that leads to breathing issues in babies. However, more research is needed to confirm this side effect. If you plan to take mirtazapine during pregnancy, talk to your doctor so that he can evaluate the pros and cons of using it.

Can people with food intolerances and allergies take mirtazapine without any risks or side effects?

Certain brands of mirtazapine may not be appropriate for people with problems digesting dairy, sugars, and other milk-based foods as these tablets contain lactose. Additionally, the orodispersible version of these tablets contains aspartame which may create trouble for people diagnosed with phenylketonuria. The oral form of mirtazapine also contains maltitol which may create issues for people intolerant to fructose. If you are unsure about the safety of taking mirtazapine due to an underlying allergy or food intolerance, talk to a doctor or pharmacist.

Can mirtazapine affect my sleep?

Mirtazapine generally makes users feel very sleepy. However, others may struggle to get sleep at night. If the sleep struggles continue with mirtazapine and start affecting your life, let your doctor know immediately.

Should I let my friends and family know that I have started taking mirtazapine?

If you have just started taking this medication, it is better to let your loved ones know so that they can support you and look out for any possible mirtazapine side effects.

What are the possible mirtazapine side effects elderly?

Most elderly people struggle with kidney issues as the organs may not work as efficiently as they used to. Consequently, their bodies may struggle to process the drug and do it more slowly than others. What this means is mirtazapine is likely to stay in their bloodstream for a longer time than others which raises the risk of side effects, such as drowsiness and confusion.


[1] Jilani TN, Gibbons JR, Faizy RM, Saadabadi A. Mirtazapine.

[2] Watanabe N, Omori IM, Nakagawa A, Cipriani A, Barbui C, Churchill R, Furukawa TA. Mirtazapine versus other antidepressive agents for depression. Cochrane Database of Systematic Reviews. 2011(12).

[3] Ostenfeld A, Petersen TS, Pedersen LH, Westergaard HB, Løkkegaard EC, Andersen JT. Mirtazapine exposure in pregnancy and fetal safety: A nationwide cohort study. Acta Psychiatrica Scandinavica. 2022 Jun;145(6):557-67.

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