No Absolute Contraindication, But Significant Pharmacodynamic Interaction Risk
Mirtazapine (Remeron) and clonidine are not absolutely contraindicated together, but their combination carries significant risk of hypertensive urgency due to opposing mechanisms of action and should be used with extreme caution or avoided when possible.
Mechanism of Interaction
The interaction stems from directly opposing pharmacodynamic effects:
- Mirtazapine acts as a central alpha-2 adrenergic receptor antagonist, which increases norepinephrine release 1
- Clonidine acts as a central alpha-2 adrenergic receptor agonist, which decreases norepinephrine release to lower blood pressure 2, 3, 4
When combined, mirtazapine can directly antagonize clonidine's antihypertensive mechanism, potentially leading to loss of blood pressure control or hypertensive crisis.
Clinical Evidence
A documented case report demonstrates this interaction can cause hypertensive urgency 5. A patient stabilized on clonidine developed hypertensive urgency after starting mirtazapine, confirming the clinical relevance of this pharmacodynamic opposition.
Research shows that mirtazapine acutely attenuates the suppressant effect of clonidine on noradrenergic neurons 6, providing mechanistic support for the clinical interaction.
FDA Labeling Position
The FDA-approved labeling for mirtazapine lists only two absolute contraindications 1:
- Concomitant use with MAOIs (or within 14 days)
- Known hypersensitivity to mirtazapine
Clonidine is not listed as an absolute contraindication, but this does not mean the combination is safe—it simply means the interaction was not severe enough to warrant FDA contraindication status.
Clinical Recommendations
When Clonidine is Essential for Blood Pressure Control:
- Avoid mirtazapine and select an alternative antidepressant without alpha-2 antagonist properties
- Consider SSRIs (sertraline, citalopram, escitalopram) 7, 8
- Consider bupropion if activation is desired 7
When Mirtazapine is Strongly Preferred:
- Discontinue clonidine and transition to alternative antihypertensive agents
- ACC/AHA guidelines note clonidine is "generally reserved as last-line because of significant CNS adverse effects" 2, 3, 4
- Multiple first-line antihypertensive options exist (ACE inhibitors, ARBs, calcium channel blockers, thiazide diuretics)
If Combination Cannot Be Avoided:
- Implement intensive blood pressure monitoring (daily or more frequent initially)
- Anticipate need for clonidine dose escalation or addition of other antihypertensives
- Never abruptly discontinue clonidine, as this can cause rebound hypertensive crisis 2, 3, 4—taper carefully if switching
Special Considerations
Clonidine withdrawal is particularly dangerous when combined with mirtazapine. The ACC/AHA guidelines specifically note that phentolamine (an alpha-blocker) is used for hypertensive emergencies induced by clonidine withdrawal 4, 2, 9. The presence of mirtazapine's alpha-2 antagonism could theoretically worsen withdrawal hypertension.
Mirtazapine offers benefits for depression with anxiety, insomnia, and appetite stimulation 7, 10, but these benefits must be weighed against cardiovascular risks when clonidine is necessary for blood pressure control.