From the Guidelines
Mirtazapine is associated with common side effects including sleep disorders, constipation or diarrhea, anxiety, increased appetite and weight gain, nausea, headache, and fatigue. According to the most recent and highest quality study 1, these side effects are dose-dependent, with higher doses typically causing more noticeable effects. The starting dose of mirtazapine is 15 mg once daily, which can be titrated according to response to treatment and tolerability to a maximum of 45 mg once daily.
Some of the key side effects to note include:
- Sleep disorders
- Constipation or diarrhea
- Anxiety
- Increased appetite and weight gain
- Nausea
- Headache
- Fatigue
It's worth noting that the sedative effects of mirtazapine are most pronounced when starting treatment or increasing the dose, but often improve with continued use. Taking mirtazapine at bedtime can help manage daytime drowsiness. While the weight gain can be concerning, this side effect makes mirtazapine particularly useful for patients with depression who have poor appetite or weight loss.
In comparison to other studies, such as 1, the side effect profile of mirtazapine is relatively consistent, with some studies noting additional side effects such as dry mouth, dizziness, and vivid dreams or nightmares. However, the most recent and highest quality study 1 provides the most up-to-date and reliable information on the common side effects of mirtazapine.
From the FDA Drug Label
Common possible side effects in people who take mirtazapine tablets include: sleepiness increased appetite, weight gain dry mouth constipation dizziness abnormal dreams
The common side effects of mirtazapine include:
- Sleepiness: reported in 54% of patients treated with mirtazapine tablets
- Increased appetite and weight gain: increased appetite was reported in 17% of patients, and weight gain of ≥ 7% of body weight was reported in 7.5% of patients
- Dry mouth: reported in 25% of patients
- Constipation: reported in 13% of patients
- Dizziness: reported in 7% of patients
- Abnormal dreams: reported in 4% of patients 2
Additionally, other common side effects reported in clinical trials include:
- Somnolence
- Asthenia
- Flu Syndrome
- Back Pain
- Myalgia
- Tremor
- Confusion
- Dyspnea
- Urinary Frequency 2
From the Research
Common Side Effects of Mirtazapine
The common side effects of mirtazapine include:
- Somnolence (drowsiness) 3, 4, 5, 6, 7
- Increased appetite 3, 4, 5, 6, 7
- Weight gain 3, 4, 5, 6, 7
- Dizziness 3
- Dry mouth 4, 5, 7
- Sedation 4, 5, 6, 7
Less Common Side Effects
Less common side effects of mirtazapine include:
- Anticholinergic-related adverse events (e.g. constipation, abnormal accommodation and vision) 4
- Adrenergic-related adverse events (e.g. palpitations, tachycardia) 4
- Neurological adverse events (e.g. tremor, vertigo) 4
- Sexual dysfunction (less common compared to other antidepressants) 4, 5, 6, 7
- Gastrointestinal symptoms (less common compared to other antidepressants) 5, 6
- Haematological parameters (e.g. agranulocytosis, neutropenia) 4, 6
Serious Side Effects
Serious side effects of mirtazapine include: