Mirtazapine Side Effects: A Complete Guide

Mirtazapine (Remeron®) is an antidepressant medication available by prescription only. Mirtazapine is primarily used to treat major depressive disorder. Like any medication, it can have potential side effects. This guide is designed to provide information about the side effects, how to mitigate them, and when to be concerned.

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What is Mirtazapine and How Does it Work?

Mirtazapine is a tetracyclic antidepressant. It works by affecting certain parts of the brain cells called presynaptic alpha-2-adrenergic receptors. Certain chemicals (neurotransmitters), serotonin and norepinephrine, are released by inhibiting or blocking these receptors. The increased levels of norepinephrine and serotonin improve depression. It is also used for the management of:

• Insomnia
• Panic disorder
• Post-traumatic stress disorder
• Obsessive-compulsive disorder
• Generalized anxiety disorder
• Social anxiety disorder
• Headaches
• Migraines

Dosage and Administration

Dosing for mirtazapine typically ranges from 15-45 mg per day. Smaller doses may be prescribed in other circumstances. 

• The starting dose is usually 15 mg, and it can be adjusted as often as every 1 to 2 weeks. 
• Because it causes sedation, mirtazapine is usually taken at night.
• Mirtazapine is available as a tablet or as an oral dissolving tablet.

Common Side Effects of Mirtazapine

Mirtazapine has several possible side effects, ranging from mild to serious. Some are physical, while others are more cognitive or mental.

Physical Side Effects

The physical side effects of mirtazapine include:

• Increased appetite
• Weight gain
• Dry mouth
• Diarrhea
• Constipation
• Nausea
• Sexual dysfunction (uncommon)
• Dizziness

These side effects can be managed in many cases.

Mental and Emotional Side Effects

Mirtazapine can cause several potential mental and emotional side effects. Mirtazapine has the potential to cause:

• Irritability
• Confusion
• Drowsiness

Sleep-Related Effects

Mirtazapine commonly causes sedation. Because of this, it’s often used off-label for sleep. Mirtazapine has been shown in studies to be better at helping with sleep than placebo but is not significantly different than other antidepressants.

Serious Side Effects

Mirtazapine also has less common and potentially serious side effects.

Serious Physical Side Effects

Some of the potentially serious side effects associated with the use of mirtazapine include:

• Pancreatitis
• Liver dysfunction
• Suppression of the bone marrow
• Low white blood cells
• Decreased platelets
• Elevated cholesterol
• Elevated triglycerides
• Serotonin syndrome

Some of these serious side effects can be mitigated by periodic monitoring and by notifying your healthcare provider if you experience any unusual symptoms or side effects.

Mental Health Risks

Mirtazapine has a black box warning for suicidal thoughts and behaviors. Some people may experience worsening depression or thoughts of self-harm with the use of mirtazapine. This side effect is more likely to occur in young adults. This risk is about the same as other antidepressants, such as selective serotonin reuptake inhibitors (SSRIs) or venlafaxine.

Allergic Reactions

Allergic reactions to mirtazapine are uncommon, but they can occur. Reactions may vary from mild to severe. Rarely, mirtazapine can cause anaphylaxis. Rashes, itching, and swelling can be signs of an allergic reaction to the medication.

Managing Mirtazapine Side Effects

Many of the side effects of mirtazapine will improve with time as the body adjusts and/or can be managed with lifestyle or dosing changes. 

When to Seek Immediate Medical Help

There are some side effects of mirtazapine, which can indicate serious medical conditions that can be life-threatening. Seek immediate medical help if you experience the following symptoms:

• Severe abdominal or back pain with nausea.
• Severe, persistent headache.
• Weakness
• Frequent muscle cramps.
• Yellowing of the skin or eyes.
• Fever with sore throat or mouth ulcers.
• Swelling of the face, especially the mouth, throat, or tongue.
• Difficulty breathing
• Confusion or dizziness
• Severe rash that is swollen, blistered, or peeling.

Tips for Managing Common Side Effects

Some of the side effects of mirtazapine can be managed by making lifestyle changes and close monitoring. 

• Sedation: Sedation is a very common side effect of mirtazapine. Taking the medication before bed can help mitigate this side effect and improve sleep. It may also be helpful to avoid other sedating medications such as antihistamines, prescription pain medications, muscle relaxers, and medications for sleep. 
• Dizziness: Dizziness or lightheadedness can be moderated by moving more slowly, especially when getting up. 
• Dry mouth: Dry mouth can be mitigated by avoiding other fluids that can cause dehydration, such as caffeine and alcohol. Frequent sips of water and using sugar-free gum or candy may also help.
• Weight gain: Regular physical activity and a healthy, balanced diet may help control this side effect. You may find meeting with a dietician to discuss dietary modifications helpful.
• Constipation: Fiber supplementation and adequate fluid intake may help lessen constipation. Sometimes, you may need a stool softener or laxative, but you should discuss this with your healthcare provider before you combine medications.

Medication Adjustments

If you are experiencing side effects, it may be tempting to adjust your dose or discontinue the medication. It’s important to discuss the side effects and symptoms with your healthcare provider before starting, changing, or discontinuing medication, including mirtazapine. 

Suddenly stopping mirtazapine can cause depression, anxiety, ringing in the ears, a feeling of restlessness, dizziness, appetite problems, insomnia, nausea, vomiting, or diarrhea.

Who Should Avoid or Be Cautious with Mirtazapine?

Mirtazapine may not be appropriate for everyone. This is one reason it’s important to discuss your health conditions, medications, and supplements with your healthcare provider when considering mirtazapine.

High-Risk Groups

• Kidney or Liver Disorders: People with liver or kidney disease may need lower doses of mirtazapine or may need to avoid it altogether. Mirtazapine is metabolized in the liver, so it should be used cautiously in this population.
• Seizure Disorders and Glaucoma: Mirtazapine should also be used with caution in people with seizure disorders or those who have glaucoma, as it has the potential to worsen these conditions. 
• Elderly: Mirtazapine is frequently used in elderly patients with decreased appetite; however, it may need to be started at a lower dose due to the risk of drowsiness.

Drug Interactions

Before taking mirtazapine, let your healthcare provider know about any medications you are taking. Mirtazapine has been shown to interact with medications and supplements, such as: 

• Other antidepressants and sedating medications: Can impact efficacy and increase sedation. 
• Warfarin (an anti-coagulant)
• Some seizure medications and antibiotics: May lower the efficacy of mirtazapine, resulting in the need for higher doses. 
• St. John’s Wort: May interfere with mirtazapine increasing the risk of side effects, so this supplement should be avoided when taking mirtazapine.

Pregnancy and Breastfeeding

Mirtazapine can be used during pregnancy and breastfeeding in some cases. In rare cases, it may cause an increased risk of post-partum hemorrhage. Generally, the benefits of maternal mental health outweigh the risks of medication, but the decision about whether to continue the medication during pregnancy should be between the patient and their healthcare team. 

As with other antidepressants, there is a slight risk of withdrawal symptoms in the infant when the medication is used during the third trimester of pregnancy.  

Mirtazapine is also generally considered safe in breastfeeding in most cases, though this should be discussed with your healthcare provider. Small amounts of mirtazapine do cross over into breast milk. 

FAQs: Mirtazapine Side Effects

Can mirtazapine cause long-term health problems? 

Mirtazapine is safe for long-term use in most patients. There is currently no evidence of long-term health problems with continued use.

Is it normal to feel drowsy or sleepy on mirtazapine?

Sedation is a very common side effect of mirtazapine. It is very common for people to feel drowsy or sleepy while taking this medication. Taking the medication at night may help prevent daytime sleepiness.

What should I do if I miss a dose?

If you forget a dose of mirtazapine, skip the dose and take the next one at your normal time. Do not double up on the medication.

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Key Takeaways

• Mirtazapine is a commonly used antidepressant.
• Common side effects include sleepiness, appetite increase, and weight gain.
• Side effects may be controlled by timing the dose of medication for the evenings.
• Diet and exercise may be used to combat weight gain with mirtazapine.
• Mirtazapine may be used during pregnancy and breastfeeding if the healthcare provider feels it’s safe.
• Don’t stop or change the dose without discussing it with your healthcare provider.
• If you have any concerns about using mirtazapine or are experiencing side effects, consult your healthcare provider for personalized advice.