Mirtazapine Side Effects and Incidence

Common Side Effects

Sedation/Somnolence is the most frequently reported side effect, occurring in approximately 23% of patients (compared to 14% with placebo), according to the American Academy of Family Physicians 1
Increased appetite occurs in about 11% of patients (versus 2% with placebo), as reported by the American Academy of Family Physicians 1
Weight gain is reported in approximately 10% of patients (versus 1% with placebo); mirtazapine and paroxetine cause higher weight gain than sertraline, trazodone, or venlafaxine, according to the American College of Physicians and the American Academy of Family Physicians 2, 1
Dry mouth occurs in approximately 25% of patients (versus 16% with placebo), as reported by the American Academy of Family Physicians 1, 3
Constipation is a frequently reported gastrointestinal side effect, according to the American College of Physicians 2

Mirtazapine causes more sedation and weight gain than most other antidepressants, according to the American College of Physicians and the American Gastroenterological Association 2, 4
Elderly patients are more susceptible to side effects, particularly sedation, orthostatic hypotension, and hyponatremia, as reported by the American Academy of Family Physicians 3
Mirtazapine has been shown to be safe in patients with cardiovascular disease and may be used for sleep in these patients, according to the American Heart Association 5
Mirtazapine's weight gain potential can be beneficial in patients with anorexia or weight loss, such as elderly patients with dementia and depression, as reported by the American Gastroenterological Association 6
Mirtazapine's sedative effects may be beneficial for patients with insomnia; it's often prescribed at bedtime, according to the American Academy of Family Physicians 7

Mirtazapine has a unique side effect profile with fewer anticholinergic, adrenergic, and serotonergic adverse effects compared to tricyclic antidepressants, as noted by the American Family Physician 8

The American Family Physician suggests that mirtazapine's side effect profile is advantageous, with minimal cardiovascular and anticholinergic effects, and essentially lacks gastrointestinal symptoms, insomnia, and sexual dysfunction common with SSRIs 8

The sedative and appetite-stimulating effects of mirtazapine can be therapeutically beneficial in specific clinical situations, such as promoting sleep in patients with insomnia when given at bedtime, as reported by the American Family Physician 8

The typical dose range is 15-30 mg/day when used for appetite stimulation, with pilot studies showing efficacy at these doses, and tolerance is limited by somnolence and weight gain as the primary side effects, occurring in 23% and 10% of patients respectively 9, 10
The American Society of Clinical Oncology aligns with the dosage recommendation, and the dosing strategy may be supported by the Annals of Oncology guidelines, which suggest that the recommended starting dosage is 15 mg/day for 4 days, then 30 mg/day, although this specific detail is not directly cited 9, 10

Mirtazapine is associated with a lower risk of gastrointestinal symptoms, such as constipation or diarrhea, compared to SSRIs, and may also cause nausea, although less commonly than serotonergic antidepressants, according to Clinical Gastroenterology and Hepatology 11, 12, 13

Mirtazapine may cause sleep disorders, but its sedative effects can improve insomnia when taken at bedtime, and it may also cause anxiety, headache, and fatigue beyond expected sedation, as reported in Clinical Gastroenterology and Hepatology 11, 12, 13