Is mirtazapine used in the treatment of anorexia nervosa?

Mirtazapine is NOT Recommended as Primary Treatment for Anorexia Nervosa

Mirtazapine should not be used as a primary or sole treatment for anorexia nervosa, as the most recent and authoritative 2023 APA guidelines make no mention of any pharmacotherapy—including mirtazapine—for the core treatment of anorexia nervosa. 1

What the Guidelines Actually Recommend

The 2023 American Psychiatric Association Practice Guideline for eating disorders is unequivocal about anorexia nervosa treatment:

• Adults with anorexia nervosa: Eating disorder-focused psychotherapy addressing eating normalization, weight restoration, and psychological aspects (1B recommendation) 1
• Adolescents/emerging adults: Family-based treatment with caregiver involvement (1B recommendation) 1
• No pharmacotherapy is recommended as part of the core treatment algorithm for anorexia nervosa 1

This stands in stark contrast to bulimia nervosa, where the APA explicitly recommends SSRIs (fluoxetine 60 mg daily) either initially or after 6 weeks of inadequate psychotherapy response 1.

The Evidence Gap for Mirtazapine

While mirtazapine theoretically seems attractive due to its appetite-stimulating and weight-gaining properties 2, the research evidence is weak:

• Small case-control study (2008): Found no significant differences in weight or BMI between mirtazapine-treated adolescents and controls, though a non-significant trend favored mirtazapine at weeks 1-3 3
• Case reports only: Individual cases show some benefit for depression and modest weight gain, but these are anecdotal 4, 5
• Mechanism unclear: One small study showed mirtazapine reduced cortisol in anorexia nervosa patients, with a trend toward BMI increase, but couldn't separate medication effects from behavioral monitoring 6

When Mirtazapine Might Be Considered (Off-Label)

Mirtazapine may have a limited adjunctive role in specific circumstances:

For comorbid depression/anxiety in weight-restored patients:

• After weight restoration has been achieved through psychotherapy
• When depression or anxiety persists despite nutritional rehabilitation
• As adjunctive treatment to ongoing psychotherapy, never as monotherapy 7

Critical safety considerations from FDA labeling:

• Increased appetite/weight gain: 17% report appetite increase, 7.5% gain ≥7% body weight 2
• Somnolence: Affects 54% of patients, causing discontinuation in 10.4% 2
• QTc prolongation risk: Exercise caution in malnourished patients with cardiac complications 2
• Agranulocytosis: Rare but serious; monitor for fever, sore throat, infection 2

The Real Clinical Algorithm

1. First-line: Eating disorder-focused psychotherapy (adults) or family-based treatment (adolescents) 1
2. Address medical complications: Nutritional rehabilitation, weight restoration with multidisciplinary team 1
3. If comorbid depression persists after weight restoration: Consider fluoxetine (which has better evidence for relapse prevention) 8 or possibly mirtazapine as adjunctive therapy 7
4. Never use mirtazapine as monotherapy or during acute malnutrition phase

Common Pitfalls to Avoid

• Don't prescribe mirtazapine hoping for weight gain alone—the evidence doesn't support this, and psychotherapy is far more effective
• Don't use during acute starvation—neurobiological changes from malnutrition complicate medication response 7
• Don't mistake appetite stimulation for treatment—anorexia nervosa is fundamentally a psychiatric disorder requiring psychological intervention, not just increased caloric intake
• Avoid abrupt discontinuation—even at low doses (15 mg), discontinuation syndrome can paradoxically worsen appetite and cause weight loss 9

The bottom line: Psychotherapy is the evidence-based treatment for anorexia nervosa. Mirtazapine has no established role in current treatment guidelines and should only be considered off-label for persistent comorbid psychiatric symptoms after weight restoration, always as an adjunct to ongoing psychotherapy. 1, 7