Mirtazapine Weight Gain: What You Should Know

By Frank DiVincenzo, MD
Medically reviewed checkmarkMedically reviewed
June 28, 2022

Mirtazapine is an antidepressant approved by the U.S. Food and Drug Administration (FDA) for treating major depressive disorder (MDD), sometimes called clinical depression.

While it may help treat depression, mirtazapine can come with a side effect that some patients find distressing: weight gain.

Two of the most common side effects of mirtazapine are increased appetite and weight gain.

In this article, I’ll talk more about this medication, how it’s used, and other medications that it can interact with.

I’ll also explain how mirtazapine can affect your appetite, metabolism, and what you can do about managing weight gain while taking it.

What is Mirtazapine?

Mirtazapine is a type of atypical antidepressant medication that is approved by the FDA for the treatment of MDD. Mirtazapine is sold under the brand name Remeron, or as a generic.

Mirtazapine works by balancing brain chemicals called neurotransmitters and improving cellular communication in the central nervous system (CNS), which includes the brain and spinal cord.

It is not fully understood how mirtazapine works, but studies have found it to be equally as effective to other popular selective serotonin reuptake inhibitor (SSRI) medications like paroxetine (Paxil), fluoxetine (Prozac), sertraline (Zoloft), and citalopram (Celexa).

Mirtazapine also may work faster than these SSRI medications, and can cause fewer side effects.

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Uses

Mirtazapine is used for treating major depressive disorder and other types of depression.

Some healthcare providers may also prescribe it for sleep disorders or insomnia, social anxiety disorder, panic disorder, fibromyalgia, or post-traumatic stress disorder (PTSD).

The benefits of mirtazapine may be felt quickly. While many antidepressants take 2-4 weeks before they show beneficial effects, mirtazapine may lead to improvements within 1-2 weeks.

Patients taking mirtazapine were found to be 74% more likely to achieve remission of depression symptoms in the first two weeks compared to people taking certain SSRIs.

Dosage

Mirtazapine is available as an oral tablet or an orally dissolving tablet.

Dosages for both options are the same.

  • Tablets available in doses of 7.5, 15, 30, and 45 mg
  • Starting dose is usually 15 mg per day once daily
  • Usually taken before bed
  • May be taken with or without food

Dosage may be increased after 1-2 weeks to determine how the medication is working.

Interactions

A drug interaction is when a medication reacts to another drug or a food, herb, or supplement, causing the medication to become less effective or cause more side effects.

There are many possible interactions with mirtazapine.

Do not take mirtazapine with any of the following:

  • Monoamine oxidase inhibitors (MAOIs): These include medications like phenelzine, linezolid, methylene blue injection, isocarboxazid, and tranylcypromine.
  • Medications that change the way the brain responds to serotonin: These include lithium, triptans, or the amino acid L-tryptophan.
  • Heart rhythm medications: This includes amiodarone and others.

There are other possible medications that can interact with mirtazapine.

Ask your pharmacist for a complete list.

Tell your healthcare provider about all the medicines and over-the-counter drugs you take, including any dietary supplements, herbs, minerals, or vitamins.

Causes of Weight Gain

Many antidepressants have weight changes as a side effect.

Mirtazapine has a more pronounced risk of weight gain, and may even be used off-label to treat lack of appetite or to help induce weight gain.

In a small study that sought to understand how mirtazapine specifically influenced body composition, the medication led to overall body weight gain, fat mass increase, and higher leptin concentrations.

Leptin is a hormone produced by fat cells that tells your brain that you are full.

But increases in this hormone can lead to leptin resistance, a condition where the brain does not get the message that you are full.

Higher levels of leptin are associated with weight gain.

Mirtazapine did not cause changes to insulin, increase insulin resistance, affect glucose metabolism, or significantly increase lipids.

Mirtazapine can lead to weight gain because it:

  • Makes you feel hungrier, so you eat more
  • Changes the way that your body stores fat
  • Changes the way that your brain responds to leptin, so your brain does not get the message that you are full

How to Manage Weight Gain

Weight gain as a side effect of a medication can be frustrating.

While some weight gain may be inevitable for some people, not everyone will gain a lot of weight while taking mirtazapine.

To manage your weight while taking mirtazapine, have a plan:

  • Eat a healthy diet that is balanced with plenty of fiber, vegetables, whole grains, lean protein, and low-fat dairy products.
  • Get regular physical activity.
  • Stay hydrated.
  • If you have trouble sensing when you should be full, measure out food portions to help prevent overeating.
  • Ask your medical provider for a referral to a dietitian to discuss a balanced meal plan.

Don’t stress. While too much weight gain may not be ideal, stressing over your weight will worsen your mental health.

Focus on the benefits you are getting from mirtazapine and work with your healthcare provider to decrease negative side effects in the ways that you can control.

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When to See a Medical Professional

If you are taking mirtazapine and are experiencing weight gain, tell your healthcare provider.

They can recommend supportive strategies to decrease side effects and find healthy ways to manage your weight.

If you are taking mirtazapine and feel that weight gain or other side effects are too much for you, do not stop taking it suddenly.

Tell your healthcare provider that you want to consider switching medications.

Depending on how long you have taken mirtazapine and what your dosage is, you may need to be slowly tapered off the medication.

Suddenly stopping can cause serious side effects or withdrawal symptoms.

If you’re having a mental health emergency, call 911 or go to the nearest emergency room. You can also get free 24/7 support from a suicide and crisis expert by calling or texting 988. If you’d prefer to chat online, you can chat with a suicide and crisis expert by visiting the Lifeline Chat.

How K Health Can Help

Think you might need a prescription for mirtazapine?

K Health has clinicians standing by 24/7 to evaluate your symptoms and determine if mirtazapine is right for you.

Get started with our free assessment, which will tell you in minutes if treatment could be a good fit. If yes, we’ll connect you right to a clinician who can prescribe medication and have it shipped right to your door.

Frequently Asked Questions

What is the average weight gain on mirtazapine?
When patients gain weight while taking mirtazapine, weight gain is on average greater than or equal to 7% of overall body weight. So for someone who weighs 150 pounds, the average weight gain would be around 10 pounds.
Does everyone gain weight on mirtazapine?
Weight gain is one of the most commonly reported side effects of mirtazapine and is reported in 12% of patients in clinical trials. Around 8% of people who were taking mirtazapine stopped taking it because of weight gain.
Does mirtazapine cause long term weight gain?
Mirtazapine changes the way that the brain responds to appetite and hormones that regulate how full you feel after meals. While much of the weight gain with mirtazapine happens within the first four weeks, it is likely that weight gain will last as long as you are taking the medication.

K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Frank DiVincenzo, MD

Dr. Frank DiVincenzo has been a physician with K Health since 2020. He grew up near Chicago, Illinois, but left the big city to go to college and then attend graduate school in Missouri. He received a Bachelor of Science in Mathematics and a Master of Science in Microbiology before graduating from the University of Missouri–Columbia School of Medicine.

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