What the label lists and what reports show
Mirtazapine side effects
Mirtazapine's FDA label: “Most common adverse reactions (≥5% or greater and twice placebo) were somnolence, increased appetite, weight gain, and dizziness.” FAERS holds 91,057 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is nausea (5,028 reports).
- Generic listed
- Boxed warning
Check it at the source: the mirtazapine FDA label on DailyMed (effective August 6, 2025, Organon LLC); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of REMERON and REMERONSolTab?REMERON and REMERONSolTab may cause serious side effects, including: See, " What is the most important information I should know about REMERON and REMERONSolTab? " Low white blood cell count. Tell your healthcare provider right away if you develop any signs or symptoms of a low white blood cell count, including: fever sore throat flu-like symptoms chills mouth or nose sores infections Serotonin syndrome. A potentially life-threatening problem called serotonin syndrome can happen when you take REMERON or REMERONSolTab with certain other medicines. […]
Source: FDA drug label, Organon LLC, effective August 6, 2025 (SPL set 98ad1917-a094-44f5-a28f-a64a8cfcd887), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common adverse reactions (≥5% or greater and twice placebo) were somnolence, increased appetite, weight gain, and dizziness.
Table 4: Adverse Reactions (≥1% and greater than placebo) in 6-Week U.S. Clinical Studies of Remeron in Patients with MDD
| Reaction | REMERON (n=453) | Placebo (n=361) |
|---|---|---|
| Asthenia | 8% | 5% |
| Flu Syndrome | 5% | 3% |
| Back Pain | 2% | 1% |
| Dry Mouth | 25% | 15% |
| Increased Appetite | 17% | 2% |
| Constipation | 13% | 7% |
| Weight Gain | 12% | 2% |
| Peripheral Edema | 2% | 1% |
| Edema | 1% | 0% |
| Myalgia | 2% | 1% |
| Somnolence | 54% | 18% |
| Dizziness | 7% | 3% |
| Abnormal Dreams | 4% | 1% |
| Thinking Abnormal | 3% | 1% |
| Tremor | 2% | 1% |
| Confusion | 2% | 0% |
| Dyspnea | 1% | 0% |
| Urinary Frequency | 2% | 1% |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedThe following adverse reactions are described in more detail in other sections of the prescribing information: Hypersensitivity [see Contraindications (4) ] Suicidal Thoughts and Behaviors [see Warnings and Precautions (5.1) ] Agranulocytosis [see Warnings and Precautions (5.2) ] Serotonin Syndrome [see Contraindications (4), Warnings and Precautions (5.3), Drug Interactions (7) ] Angle-Closure Glaucoma [see Warnings and Precautions (5.4) ] QT Prolongation and Torsades de Pointes [see Warnings and Precautions (5.5) ] Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) [see Warnings and Precautions (5.6) ] Increased Appetite and Weight Gain [see Warnings and Precautions (5.7) ] Somnolence [see Warnings and Precautions (5.8) ] Activation of Mania or Hypomania [see Warnings and Precautions (5.9) ] Seizures [see Warnings and Precautions (5.10) ] Elevated Cholesterol and Triglycerides [see Warnings and Precautions (5.11) ] Hyponatremia [see Warnings and Precautions (5.12) ] Transaminase Elevations [see Warnings and Precautions (5.13) ] Discontinuation Syndrome [see Warnings and Precautions (5.14) ] Use in Patients with Concomitant Illness [see Warnings and Precautions (5.15) ] Most common adverse reactions (≥5% or greater and twice placebo) were somnolence, increased appetite, weight gain, and dizziness.
Source: FDA drug label, Organon LLC, effective August 6, 2025 (SPL set 98ad1917-a094-44f5-a28f-a64a8cfcd887), via openFDA; the full label on DailyMed
What do FAERS reports show?
91,057 reports list mirtazapine among the medicines taken, each a report of something that happened, not proof the medicine caused it; 13,998 are coded as a death and 37,233 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 19 reactions below, 12 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Mirtazapine: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions