The recommended starting dose when treating depression is mirtazapine 15 mg, taken once daily at bedtime. Your healthcare provider may increase the dosage if symptoms continue, or decrease the dose if side effects occur.The maximum recommended dose of mirtazapine is 45 mg per day.he recommended starting dose when treating depression is 15 mg, taken once a day. The dose of mirtazapine (Remeron ®) that your healthcare provider prescribes will vary, depending on a number of factors, including: