How to Take Mirtazapine
Start mirtazapine at 15 mg once daily, taken in the evening before bedtime, and increase to 30-45 mg daily if needed after 1-2 weeks based on response. 1
Starting Dose and Timing
- Initial dose: 15 mg once daily 1
- Take in the evening, preferably at bedtime 1
- This timing leverages mirtazapine's sedating properties to help with sleep while minimizing daytime drowsiness 2
Dose Titration
If inadequate response after 1-2 weeks:
- Increase to 30 mg daily 1
- Can further increase to maximum 45 mg daily if needed 1
- Wait at least 1-2 weeks between dose changes to allow adequate time to assess response 1
The evidence supports that increasing from 15 mg to 30 mg in early non-responders (those without ≥20% symptom improvement at week 1) leads to significantly better outcomes 3. However, increasing beyond 30 mg to 45 mg shows less clear benefit 3.
Special Dosing Considerations
Dose reductions may be needed for:
- Elderly patients: Start lower due to 40% reduced clearance in elderly males and 10% in elderly females 1
- Renal impairment: 30% reduction in clearance (GFR 11-39) or 50% reduction (GFR <10) 1
- Hepatic impairment: 30% reduction in clearance 1
- Obesity (BMI ≥28): Consider 22.5-30 mg/day (29% reduced clearance) 4
Drug interactions requiring dose adjustment:
- With paroxetine: Reduce to 22.5-30 mg/day (27% reduced clearance) 4
- With fluvoxamine: Reduce to 15 mg/day (51% reduced clearance) 4
- With cimetidine: Decrease dose (>50% increase in mirtazapine levels) 1
- With strong CYP3A4 inhibitors (ketoconazole, clarithromycin): Decrease dose 1
- With strong CYP3A4 inducers (carbamazepine, phenytoin, rifampin): May need dose increase (approximately 2-fold increase in clearance) 1
Administration Guidelines
- Can be taken with or without food (minimal effect on absorption) 1
- Swallow tablets whole
- Do not stop abruptly - taper gradually to avoid withdrawal symptoms 1
- Steady-state levels achieved within 5 days 1
- Peak plasma levels occur approximately 2 hours after dosing 1
Important Safety Precautions
Do NOT take mirtazapine if:
- Currently taking or stopped an MAOI within the past 14 days 1
- Wait at least 14 days after stopping mirtazapine before starting an MAOI 1
Screen for bipolar disorder before starting - mirtazapine can trigger manic episodes in susceptible individuals 1
Common Side Effects to Anticipate
- Increased appetite and weight gain (particularly relevant at lower doses) 5, 1
- Sedation/drowsiness (paradoxically more common at 15 mg than higher doses) 5, 1
- Constipation or diarrhea 5
- Dry mouth 6
Serious but rare side effects requiring immediate medical attention:
- Fever, sore throat, flu-like symptoms (possible low white blood cell count) 1
- Signs of serotonin syndrome when combined with other serotonergic drugs 1
Clinical Context by Indication
For depression: The standard approach outlined above applies 1
For insomnia in palliative care: Mirtazapine is especially effective when depression and anorexia coexist 7
For gastroparesis/functional GI disorders: Start at 7.5-30 mg/day 8, with guidelines suggesting 15 mg once daily as the starting dose with titration to maximum 45 mg/day 5
For IBS with abdominal pain: 15 mg once daily starting dose, titrating to 45 mg maximum 5, 9
The evidence consistently supports evening dosing to maximize sleep benefits while therapeutic effects on mood, appetite, and pain develop over 1-2 weeks of treatment.