Mirtazapine Side Effects: Sleep, Appetite and What to Know

Written by the Lyte Psychiatry clinical team. Clinically reviewed by Ana G., LPC, and medically reviewed by Dr. Akinwande Akintola, MD, supervising physician. Last reviewed: November 4, 2026.

Mirtazapine side effects most often include drowsiness, dizziness and increased appetite and weight, according to MedlinePlus. Mirtazapine, sold under the brand name Remeron, is an antidepressant approved to treat depression. Because it can make people sleepy and hungrier, its effects on sleep and appetite are a common topic to discuss with a prescriber before and during treatment.

This article is for adults who have been prescribed mirtazapine, are considering it with a clinician or care for someone who takes it. It explains what the medicine is, why sleep and appetite come up, common and serious side effects, safety warnings, questions to ask and when to call your prescriber right away.

This article is general information, not a medical recommendation. Do not start, stop or change any medication without talking to your prescriber.

What is mirtazapine (Remeron)?

Mirtazapine is a prescription antidepressant used to treat depression. MedlinePlus explains that it works by increasing certain types of activity in the brain to maintain mental balance, and notes that it is sometimes prescribed for other uses, which you should discuss with your doctor or pharmacist.

It comes as a regular tablet and as a tablet that dissolves on the tongue. MedlinePlus describes it as usually taken once a day at bedtime, exactly as prescribed. Your prescriber decides the amount and schedule based on your health, other medicines and response. This article does not give dosing information.

Why does mirtazapine affect sleep?

Drowsiness is one of the most common effects of mirtazapine, which is one reason it is usually taken at night. MedlinePlus lists drowsiness, dizziness and increased weight and appetite as common side effects.

For some people with depression who also struggle to sleep, feeling sleepy at night may be welcome. For others, drowsiness can carry over into the morning. MedlinePlus advises not to drive or operate machinery until you know how the medicine affects you. If you feel groggy during the day, tell your prescriber rather than adjusting the medicine yourself.

Example: a person who starts mirtazapine might notice they fall asleep faster but feel slow and foggy until mid-morning for the first week or two. This is a hypothetical example. Patterns like this are worth writing down and sharing, because your prescriber can only adjust the plan based on what they know.

Why does mirtazapine affect appetite and weight?

Increased appetite and weight gain are common side effects listed for mirtazapine. Whether that matters depends on your situation and health goals, which is why it is important to talk openly about it with your prescriber.

Depression itself can change appetite. MedlinePlus notes that emotions such as sadness, depression or grief can cause loss of appetite, and that unexplained weight loss is a reason to contact a provider. On the other hand, people with diabetes, heart conditions or concerns about weight gain may want to discuss monitoring plans. Bring up these concerns before starting, not only after changes appear.

Common mirtazapine side effects such as hunger and sleepiness are not a sign that something is wrong with you or that you lack willpower. They are known effects of the medicine. Weighing yourself at the same time each week and noting cravings or late-night snacking can give you and your prescriber clear information to discuss.

What other side effects and warnings should you know?

Like all antidepressants, mirtazapine carries important safety warnings. MedlinePlus notes that it may increase the risk of suicidal thoughts and actions in children, teenagers and young adults under 24, especially in the first few months of treatment or when the dose changes.

The U.S. Food and Drug Administration (FDA) boxed warning on antidepressants asks families and caregivers to watch closely for new or worsening symptoms, such as agitation or unusual changes in behavior, and to contact the prescriber promptly. Other warnings on the MedlinePlus page include:

• Telling your doctor if you take, or recently stopped, a monoamine oxidase (MAO) inhibitor.
• Asking your doctor about alcohol, which MedlinePlus says can make side effects worse.
• Sharing all prescription and nonprescription medicines, vitamins and supplements you take.
• Telling your doctor if you are pregnant, planning pregnancy or breastfeeding.

Which side effects need urgent attention?

Some side effects are rare but serious. MedlinePlus advises calling your doctor right away or getting emergency care for symptoms such as:

• Signs of infection, such as fever, chills, sore throat or mouth sores.
• Fever, sweating, confusion, fast or irregular heartbeat, severe muscle stiffness or twitching, agitation or hallucinations.
• Chest pain or a fast heartbeat.
• Unusual bleeding or bruising.
• Rash, hives, swelling of the face or throat, or trouble breathing or swallowing.
• Seizures.
• Eye pain, vision changes or eye swelling or redness.

Call 911 for trouble breathing, a seizure or any symptom that feels life-threatening.

How long does mirtazapine take to work?

Antidepressants generally take weeks to show their full effect on mood. As of October 2026, MedlinePlus explains that antidepressants may take 4 to 8 weeks to work, and that treatment often continues for 6 to 12 months or longer.

The National Institute of Mental Health (NIMH) notes that early side effects are common and often fade over time, and that finding the right treatment may take some trial and error. Effects on sleep or appetite may appear before changes in mood. Track how you feel and share it at follow-up visits.

How can you get the most from treatment step by step?

A few habits can make medication treatment safer and more useful. Use these steps after your prescriber starts mirtazapine.

1. Take it exactly as prescribed. Do not change the amount or timing on your own.
2. Keep a simple log. Note mood, sleep, appetite, weight and daytime grogginess each day for the first several weeks.
3. Plan for drowsiness. Avoid driving until you know how the medicine affects you.
4. Talk about alcohol. Ask your prescriber whether any alcohol is safe for you.
5. Keep follow-up visits. Bring your log and questions.
6. Never stop suddenly. MedlinePlus says not to stop mirtazapine without talking to your doctor, who will probably lower the dose gradually.
7. Add non-medication supports. Therapy, regular sleep and wake times, and daily movement often work alongside medication.

What questions should you ask your prescriber?

Questions help you understand your plan and make shared decisions. Consider bringing this checklist.

• Why are you recommending this medicine for me?
• What side effects are most likely, and which ones should I call about?
• How will we monitor my sleep, appetite and weight?
• Does it interact with my other medicines or supplements?
• What should I do if I miss a dose?
• How long will I likely take it, and how would we stop it safely?
• What other options, including therapy, could help me?

What if insomnia continues?

If mirtazapine side effects or ongoing sleep problems are a concern, ask about other approaches too. If sleep problems persist, a separate evaluation for insomnia may help. The American Academy of Sleep Medicine notes that cognitive behavioral therapy for insomnia (CBT-I) is recommended for chronic insomnia in adults, and it can be done in person, by video or online.

Ongoing sleep trouble can also be a sign that depression needs a different approach. Tell your prescriber how you are sleeping at every visit.

When should you get help sooner?

Contact your prescriber promptly, or get emergency care, for these red flags:

• New or worsening thoughts of suicide or self-harm.
• Agitation, restlessness, panic or unusual changes in behavior.
• Signs of infection, such as fever or sore throat.
• Severe drowsiness, confusion or fainting.
• Any of the serious side effects listed above.
• Depression that is getting worse rather than better.

What should Texans know about medication care?

Many Texans see a psychiatric clinician for medication management, in person or by telehealth. The U.S. Department of Health and Human Services explains that providers generally must be licensed or otherwise permitted to practice in the state where the patient is located, and these rules vary by state. That means your physical location during a video visit matters.

Lyte Psychiatry offers telehealth visits to patients who are physically located in Texas at the time of the visit. Prescribing decisions are always individual and depend on an evaluation.

Getting support in Texas

If you have questions about mirtazapine side effects or whether your current treatment is working, a medication management visit can help. Lyte Psychiatry offers therapy, psychiatric evaluation and medication management in Texas.

In-person visits are available at Lyte Psychiatry's clinic in Pantego, in the Dallas–Fort Worth area. All Lyte Psychiatry services are available in Spanish. Most new patients are seen within 1–2 business days. Weekend appointments are limited. Availability, insurance and clinician fit require confirmation.

Learn more about medication management or depression care. Related reading: how to handle medication side effects, how long people take antidepressants and CBT-I for insomnia.

Lyte Psychiatry is an outpatient practice. It does not provide inpatient care, crisis or after-hours coverage, medically supervised detox, or intensive outpatient or partial hospitalization programs.

If you are in a mental-health crisis in the United States, call or text 988. Call 911 for immediate danger.

Educational information, not a diagnosis or individual treatment plan.