Can Remeron (Mirtazapine) Be Taken PRN (As Needed)?
No, mirtazapine should not be taken on an as-needed (PRN) basis—it requires consistent nightly dosing to be effective for either depression or insomnia. 1
Why PRN Dosing Does Not Work
Mirtazapine has a half-life of 20–40 hours, meaning it takes several days to reach steady-state therapeutic blood levels; PRN use cannot provide the consistent drug exposure required for clinical benefit. 2, 1
The American Academy of Sleep Medicine explicitly states that mirtazapine must be taken nightly on a scheduled basis, not as needed, because its sedating and antidepressant effects depend on maintaining stable plasma concentrations. 1
Unlike short-acting hypnotics such as zaleplon or zolpidem that can be used occasionally for sleep-onset insomnia, mirtazapine's mechanism—blocking presynaptic α₂-adrenergic receptors and enhancing noradrenergic and serotonergic neurotransmission—requires continuous daily administration to produce therapeutic effects. 2, 3, 1
Appropriate Use of Mirtazapine
For Depression
The American College of Physicians recommends that mirtazapine be taken once daily, preferably at bedtime, with therapeutic response assessed after 6–8 weeks of continuous treatment. 4, 5
Treatment should continue for 4–9 months after achieving satisfactory response in first-episode major depressive disorder, and even longer for patients with recurrent episodes. 4
The recommended starting dose is 15 mg once daily at bedtime, with an effective dosage range of 15–45 mg/day. 2, 6, 5
For Insomnia (Third-Line Option)
When used specifically for insomnia in patients with comorbid depression or anxiety, mirtazapine is positioned as a third-line pharmacologic option after benzodiazepine-receptor agonists have failed. 1
Mirtazapine's sedating effects are most pronounced at lower doses (7.5–15 mg) due to histamine H₁-receptor antagonism, but nightly scheduled dosing is still required—not PRN use. 2, 3, 1
The American Academy of Sleep Medicine mandates that any pharmacotherapy for chronic insomnia must be combined with Cognitive Behavioral Therapy for Insomnia (CBT-I), which itself requires nightly implementation of stimulus control, sleep restriction, and cognitive restructuring—not intermittent application. 1
Alternative PRN Options for Occasional Insomnia
If you need a medication specifically for intermittent, as-needed use for sleep:
Zaleplon 10 mg (5 mg if age ≥65 years) has an ultrashort half-life (~1 hour) and can be used PRN for truly occasional sleep-onset difficulty, providing rapid sleep initiation without next-day sedation. 1
Zolpidem 10 mg (5 mg if age ≥65 years) may be used PRN for occasional sleep-onset problems, though the American Academy of Sleep Medicine recommends scheduled nightly dosing for chronic insomnia rather than intermittent use. 1
However, PRN hypnotic use is not appropriate for chronic insomnia; the FDA and American Academy of Sleep Medicine specify that benzodiazepine-receptor agonists are intended for short-term (≤4 weeks) scheduled use, not intermittent dosing. 1
Critical Safety Considerations
Abruptly stopping mirtazapine after regular use may cause withdrawal symptoms; the FDA label warns that discontinuation should be gradual under medical supervision. 5
Mirtazapine carries FDA warnings for increased suicidal thoughts and behaviors in young adults, new or worsening depression, agitation, panic attacks, and other mood changes—monitoring is essential during the first 1–2 weeks of treatment. 5, 4
Common side effects include somnolence, increased appetite, weight gain, and dry mouth; these effects are dose-dependent and occur with regular use, not PRN dosing. 4, 2, 3, 6
Common Pitfalls to Avoid
Do not prescribe mirtazapine PRN thinking it will work like a short-acting sleep aid; its pharmacokinetics and mechanism of action require daily dosing to achieve therapeutic effect. 1, 2
Do not use mirtazapine for brief (3-week) courses of mild depression; it requires 6–8 weeks to adequately assess therapeutic response and is most effective in moderate-to-severe depression. 4
When using mirtazapine for insomnia, do not initiate it without concurrent CBT-I, as behavioral therapy provides more durable benefits and is mandated as first-line treatment by guideline societies. 1