Common and Serious Side Effects of Mirtazapine (Remeron) and Their Incidence
Mirtazapine commonly causes sedation, increased appetite, weight gain, and dizziness as side effects, while serious adverse effects include rare cases of agranulocytosis, serotonin syndrome, and severe skin reactions. 1, 2
Common Side Effects
- Sedation/Somnolence: This is the most frequently reported side effect, occurring in approximately 23% of patients (compared to 14% with placebo) 1, 3
- Increased appetite: Occurs in about 11% of patients (versus 2% with placebo) 1, 2
- Weight gain: Reported in approximately 10% of patients (versus 1% with placebo); mirtazapine and paroxetine cause higher weight gain than sertraline, trazodone, or venlafaxine 1
- Dizziness: Common side effect that may affect daily functioning 2, 3
- Dry mouth: Occurs in approximately 25% of patients (versus 16% with placebo) 1
- Constipation: Frequently reported gastrointestinal side effect 1, 2
Serious Side Effects
- Hematological effects: Low white blood cell count (agranulocytosis) is rare but serious, occurring in approximately 1 in 1,000 patients 2, 4
- Serotonin syndrome: Life-threatening condition that can occur when mirtazapine is combined with other serotonergic medications, presenting with agitation, confusion, fast heart rate, tremors, and hyperthermia 2
- Angle-closure glaucoma: Can cause eye pain, vision changes, and swelling or redness around the eye 2
- Cardiac rhythm problems: Including QT prolongation, particularly in susceptible individuals 2
- Severe skin reactions: Can include rash, fever, swollen glands, and multi-organ involvement (liver, kidney, lung, heart) - potentially fatal 2
- Seizures: Mirtazapine may lower the seizure threshold in susceptible individuals 2
Metabolic Effects
- Increased cholesterol and triglyceride levels: Mean increases of 3-4% have been reported 5
- Liver enzyme elevations: Usually transient and resolve with discontinuation 5
- Hyponatremia: Low sodium levels, particularly in elderly patients, which can be serious or fatal in severe cases 2
Psychiatric Effects
- Mania/hypomania: Particularly in patients with bipolar disorder history 2
- Suicidal thoughts: Increased risk in children, adolescents, and young adults, especially during the first few months of treatment (mirtazapine is not approved for use in children) 2
- Discontinuation syndrome: Abrupt cessation can cause dizziness, irritability, anxiety, sweating, and other withdrawal symptoms 2
Special Considerations
- Elderly patients: More susceptible to side effects, particularly sedation, orthostatic hypotension, and hyponatremia 1
- Cardiovascular disease: Mirtazapine has been shown to be safe in patients with cardiovascular disease and may be used for sleep in these patients 1
- Weight gain potential: Can be beneficial in patients with anorexia or weight loss, such as elderly patients with dementia and depression 1
- Sleep disturbances: Mirtazapine's sedative effects may be beneficial for patients with insomnia; it's often prescribed at bedtime 1, 3
Incidence Compared to Other Antidepressants
- Mirtazapine has fewer anticholinergic effects than tricyclic antidepressants 5
- Unlike SSRIs, mirtazapine has minimal sexual side effects 6
- Mirtazapine causes more sedation and weight gain than most other antidepressants 1
- Mirtazapine has a lower risk of gastrointestinal side effects (nausea, vomiting) compared to SSRIs and SNRIs 5, 6
Clinical Management of Side Effects
- Start with a low dose (7.5-15 mg) at bedtime to minimize daytime sedation 1, 3
- Monitor weight regularly, especially during the first few months of treatment 2
- Consider blood work to monitor for rare but serious hematological effects 2
- Taper gradually when discontinuing to minimize withdrawal symptoms 2
- Avoid combining with other serotonergic medications to prevent serotonin syndrome 2
Mirtazapine's unique side effect profile makes it particularly useful for patients with insomnia, anxiety, or weight loss, but requires careful monitoring for sedation and weight gain 1, 6.