Gastrointestinal Side Effects of Mirtazapine

Introduction to Mirtazapine-Induced Constipation

• The American Gastroenterological Association lists constipation as one of the frequent side effects of Mirtazapine, along with sleep disturbances, diarrhea, anxiety, increased appetite, and weight gain 1
• Mirtazapine is associated with constipation, although this occurs less frequently compared to other antidepressants, with a typical starting dose of 15 mg once daily and can be titrated up to a maximum of 45 mg once daily 1

Comparison with Other Antidepressants

• Tricyclic antidepressants cause constipation more frequently due to their anticholinergic effects 1, 2, 3, 4
• The NCCN Palliative Care Guidelines identify anticholinergic medications, including antidepressants, as known causes of constipation 2, 3, 4

Clinical Implications

• The American College of Gastroenterology recommends the use of osmotic laxatives like polyethylene glycol (PEG) as first-line therapy for constipation induced by Mirtazapine 5
• The National Comprehensive Cancer Network recommends the addition of stimulant laxatives like bisacodyl or senna for persistent constipation 2, 5, 6
• Adequate fluid intake and physical activity should be promoted to help manage constipation 2, 5
• A high-fiber diet can be helpful for patients with adequate fluid intake 2, 6