10 Mirtazapine Side Effects You Should Know About

Depression is a medical condition that can cause you to feel sad and disconnected. Treatment can include a combination of therapy, prescription medication, and developing coping skills. 

If your healthcare provider decides medication should be a part of your treatment plan, they may prescribe mirtazapine (Remeron). Mirtazapine is a first-choice medication treatment option for depression. But as with all medications, it comes with a number of possible side effects. Some are mild and can be managed, but others are more serious.

Here, we’ll review 10 mirtazapine side effects you should be aware of.

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1. Drowsiness

Drowsiness is a common mirtazapine side effect — with more than 50% of people in clinical trials reporting it. It’s recommended that you take mirtazapine at bedtime to best manage this side effect.

Drowsiness from mirtazapine may be beneficial for people with insomnia. But it can be bothersome for others. Be sure to avoid driving or operating heavy machinery after taking it. It’s also a good idea to avoid alcohol, since it can make this side effect worse. If your drowsiness doesn’t go away, or if it becomes worse, talk to your healthcare provider. They can help decide what action to take. 

2. Dizziness

Dizziness is another common side effect of mirtazapine. If you feel dizzy after taking mirtazapine, it’s important to move slowly when sitting up or standing. This can help you avoid falls, which can be dangerous — especially for older adults. 

If your dizziness worsens or doesn’t go away over time, it’s important to discuss it with your healthcare provider. Dizziness can be caused by things other than medication, so it’s important for your provider to determine the cause of yours. They can then help you find the best way to manage it.  

3. Weight gain

Mirtazapine is more likely to cause weight gain than other antidepressants. That’s because it can make you feel hungrier than normal. It’s important to aim for a healthy diet and regular exercise to help manage this side effect. Adopting these habits can help with your depression symptoms, too.

If you notice weight gain, talk to your healthcare provider to determine whether it's caused by mirtazapine. This may be one of the effects that stabilizes over time as you get used to the medication. But if weight gain is a concern for you, there are other antidepressant options — such as fluoxetine (Prozac) — which are less likely to cause weight gain. 

4. Dry mouth

Mirtazapine can cause dry mouth. About 1 in 4 people experienced dry mouth in clinical studies. Drinking plenty of water can help relieve this side effect. You can also try sugar-free gum or candy as well as over-the-counter (OTC) saliva substitutes. 

5. Constipation

Constipation is another possible side effect of mirtazapine. It’s related to the “drying out” effect of mirtazapine that also causes dry mouth. To address this side effect, it’s important to drink plenty of water. If that doesn’t work, you can also try an OTC stool softener or laxative. 

Constipation can be caused by many factors, so talk to your healthcare provider if it becomes a problem for you. 

6. Nausea

Mirtazapine may also cause nausea, but it’s not as common as the other side effects mentioned so far. The chance of having nausea with mirtazapine is lower than it is for certain other antidepressants, such as sertraline (Zoloft). 

If you experience nausea, try taking mirtazapine with food. You can also try eating foods, teas, or supplements that contain ginger. If nausea doesn’t improve with time, or after you’ve made changes to how you take mirtazapine, let your healthcare provider know.

7. Low sodium levels

Mirtazapine can sometimes cause low sodium levels. This is a rare side effect of mirtazapine, but it’s also a serious one. Symptoms of low sodium levels include:

• Headache

• Confusion

• Weakness

• Difficulty with concentration and memory

If you experience any of these, talk to your healthcare provider right away. More serious symptoms include hallucinations, fainting, or seizures. It’s important to seek emergency care right away if you experience these. 

8. Higher cholesterol levels

A rise in cholesterol levels is another possibility when taking mirtazapine. In clinical trials, 15% of people taking mirtazapine had cholesterol that jumped above the normal range. This may be linked to weight gain while taking mirtazapine. 

Your healthcare provider will likely keep an eye on your cholesterol levels while you’re taking mirtazapine. Certain lifestyle changes can also help you manage this side effect. 

9. Flu-like symptoms

Experiencing flu-like symptoms while taking mirtazapine may not seem like a big deal. But it can actually be a sign of a rare but serious side effect. This includes symptoms like:

• Fever

• Chills

• Sore throat

• Mouth and nose sores

These symptoms could be a sign of a low number of white blood cells in your body. White blood cells help you fight infections. If your levels fall too low, you can feel like you have the flu. If you experience these symptoms, inform your healthcare provider right away.

10. Suicidal thoughts

While uncommon, mirtazapine can potentially increase the risk of suicidal thoughts and behaviors, especially in young adults under 25 years old. This is considered a serious boxed warning (the strictest warning from the FDA). In fact, all antidepressants have this warning.

It’s important to watch for a change in mood or behavior while taking mirtazapine. This is especially important when first starting the medication or when changing your dose. Contact your healthcare provider right away if these symptoms appear.

When should I contact my healthcare provider about side effects from mirtazapine?

It’s important to inform your healthcare provider about both common and serious side effects. These concerns may subside once you’ve taken the medication for a certain amount of time, but it’s helpful to keep your provider in the loop. They may be able to suggest ways to manage the side effect, adjust the dose, or change the medication altogether. Don’t stop taking mirtazapine without talking to your healthcare provider first. 

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Written by:

Hindu Rao, PharmD, APh, BCACP

Hindu Rao, PharmD, APh, BCACP is a clinical assistant professor of pharmacy practice at Chapman University School of Pharmacy and a clinical pharmacist at Providence Medical Foundation. She specializes in chronic disease management and has her board certification in ambulatory care.

Edited by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Reviewed by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

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If you or someone you know is having thoughts of suicide, help is available. Call 988 to reach the National Suicide Prevention Lifeline or text HOME to 741-741 to reach the Crisis Text Line.