What is the recommended dosing for mirtazapine (Remeron) in the treatment of anxiety?

Mirtazapine Dosing for Anxiety

Start mirtazapine at 15 mg once daily at bedtime, and increase up to a maximum of 45 mg daily if needed, with dose adjustments made no more frequently than every 1-2 weeks. 1

Starting Dose and Titration

• Begin with 15 mg orally once daily, preferably in the evening prior to sleep 1
• If inadequate response occurs after 1-2 weeks of assessment, increase the dose toward the maximum of 45 mg per day 1
• Do not adjust doses more frequently than every 1-2 weeks to allow sufficient time to evaluate response to the current dose 1
• The lower starting dose (7.5 mg) mentioned in older Alzheimer's guidelines 2 is not the FDA-recommended starting dose for anxiety or depression in general adult populations 1

Mechanism Supporting Anxiolytic Effects

• Mirtazapine blocks presynaptic alpha-2 adrenergic receptors and postsynaptic 5-HT2 and 5-HT3 receptors, which contributes to both antidepressant and anxiolytic effects 3
• The drug enhances noradrenergic and serotonergic neurotransmission specifically via 5-HT1 receptors 4, 5
• Mirtazapine is particularly effective for anxiety symptoms associated with depression and may reduce the need for concomitant anxiolytic medications 4, 6

Specific Advantages for Anxiety

• Mirtazapine is potent, well-tolerated, and promotes sleep, making it especially useful when anxiety is accompanied by insomnia 2, 7
• The drug demonstrates important anxiolytic effects that may be related to its unique pharmacodynamic properties 5
• It is effective in patients with depression and associated anxiety symptoms 2, 4
• Limited data suggest beneficial anxiolytic and sedative effects beyond its antidepressant action 3

Timeline for Response

• Begin assessing therapeutic response and adverse effects within 1-2 weeks of starting treatment 7
• Some patients show improvement in anxiety and depressive symptoms as early as 1 week after starting treatment 4, 8
• If inadequate response occurs within 6-8 weeks, treatment modification is strongly recommended 7

Common Side Effects to Monitor

• Somnolence/sedation is the most common side effect, particularly at lower doses due to H1 antihistaminic activity 3, 5, 8
• Paradoxically, sedation appears less frequent at higher therapeutic doses (≥15 mg) 4
• Increased appetite and weight gain are common 3, 5, 8
• Additional effects include dizziness, dry mouth, and constipation or diarrhea 7, 3
• Mirtazapine does not typically cause sexual dysfunction, unlike SSRIs 5

Important Dosing Considerations

• Screen for bipolar disorder, mania, or hypomania before initiating treatment 1
• Allow at least 14 days between discontinuing an MAOI and starting mirtazapine, and vice versa 1
• Gradually reduce the dose rather than stopping abruptly to minimize withdrawal symptoms 1
• Dose adjustments may be needed with strong CYP3A4 inducers (increase dose) or inhibitors (decrease dose) 1

Duration of Treatment

• Continue treatment for 4-9 months after satisfactory response in first-episode patients 7
• Patients with recurrent anxiety or depression may benefit from longer treatment duration 7

Alternative Considerations

• If inadequate response to mirtazapine occurs, consider switching to an SSRI or SNRI, or adding another antidepressant with a different mechanism 7
• For refractory cases with prominent insomnia, alternatives include trazodone or other sedating agents 7