Can Mirtazapine Cause Shortness of Breath?
Yes, mirtazapine can cause shortness of breath (dyspnea), though this is an uncommon adverse effect listed in the FDA drug label, occurring in approximately 1% of patients in clinical trials. 1
Evidence from FDA Drug Label
The official FDA prescribing information for mirtazapine lists dyspnea (shortness of breath) as a documented adverse reaction in the respiratory system category, occurring in 1% of patients receiving mirtazapine compared to 0% in placebo-treated patients during 6-week controlled trials. 1
Clinical Context and Mechanism
While dyspnea is a recognized side effect, it's important to understand the broader context:
Sedation is the predominant respiratory effect: The most common adverse reaction with mirtazapine is somnolence, occurring in 54% of patients versus 18% with placebo, which can sometimes be perceived as difficulty breathing or chest heaviness. 1
Cardiovascular safety profile: Mirtazapine has minimal cardiovascular effects at therapeutic doses and has been shown to be safe in patients with cardiovascular disease, making primary cardiac causes of breathlessness less likely. 2
Paradoxical use in breathlessness: Interestingly, mirtazapine has been studied as a potential treatment for chronic breathlessness in advanced lung disease, though a large 2024 randomized controlled trial found it ineffective for this indication and potentially caused adverse reactions. 3
Clinical Differentiation
When a patient on mirtazapine reports shortness of breath, consider:
Timing of onset: If breathlessness began shortly after starting mirtazapine or dose escalation, drug-related dyspnea is more likely. 1
Sedation versus true dyspnea: Excessive sedation (19% incidence) may manifest as perceived breathing difficulty rather than true respiratory compromise. 1
Underlying conditions: Patients with pre-existing pulmonary or cardiac disease may experience worsening breathlessness, though this may be disease progression rather than drug effect. 3
Management Approach
Assess severity: Determine if this represents subjective breathlessness or objective respiratory compromise with hypoxia or altered respiratory rate. 1
Review concurrent medications: Combining mirtazapine with other sedating medications can lead to excessive sedation and potentially dangerous respiratory depression, according to oncology guidelines. 4
Consider dose adjustment: If breathlessness is mild and other benefits outweigh this effect, reducing the dose may help, as sedative effects are dose-dependent. 4
Discontinuation if necessary: If dyspnea is clinically significant, gradual tapering over 10-14 days is recommended rather than abrupt discontinuation. 4
Important Caveats
The 1% incidence means this is an uncommon but real adverse effect that should be on the differential diagnosis. 1
Most adverse reactions leading to discontinuation in clinical trials were related to somnolence (10.4%) rather than respiratory symptoms. 1
Elderly patients may be more sensitive to all adverse effects of mirtazapine, including potential respiratory symptoms. 4