Mirtazapine is mainly used as a second or third line antidepressant. However, it has many other beneficial uses, ranging from the treatment of anxiety and insomnia to improving symptoms of OCD and PTSD. Mirtazapine is a drug with a complex mechanism of action, but it shows promising results in a number of off-label uses.

Note: By writing this post, we are not recommending this drug. Some of our readers who were already taking the drug requested that we commission a post on it, and we are simply providing information that is available in the scientific literature. Please discuss your medications with your doctor.

What is Mirtazapine?

Mirtazapine has a number of interactions with other medications that you should be aware of [R]:

  • H2 Antagonists (cimetidine, ranitidine, etc.) decrease the breakdown of mirtazapine resulting in increased levels of the drug in the body.
  • Phenytoin and carbamazepine increase the breakdown of mirtazapine resulting in decreased levels of the drug in the body.
  • Antibiotics (macrolides: erythromycin, clarithromycin, etc.) and antifungals (metronidazole) can also cause increased levels of mirtazapine in the body when taken together.
  • Beta-blockers (metoprolol, propranolol, etc.)vasodilators (hydralazine, prazosin, doxazosin, etc.), centrally-acting antihypertensives (clonidine), ACEIs (lisinopril, captopril, etc.), calcium channel antagonists (nifedipine and verapamil), and thiazide diuretics (hydrochlorothiazide) taken with mirtazapine can increase the risk of postural hypotension (low blood pressure associated with a change in body position).
  • Anticoagulants (warfarin) can have an increased effect when taken with mirtazapine.
  • Antihistamines (chlorphenamine, hydroxyzine, promethazine, cetirizine, loratadine, etc.), phenothiazines (prochlorperazine), nabilone, and hyoscine can cause increased sedation when taken with mirtazapine.
  • Hypnotics (temazepam and promethazine), benzodiazepines (diazepam, alprazolam, lorazepam, etc.), antipsychotics (chlorpromazine, haloperidol, clozapine, and olanzapine), opioids (oxycodone, hydrocodone, codeine, morphine, etc.), and buprenorphine can also cause increased sedation when taken with mirtazapine.
  • Monoamine oxidase inhibitors (MAOIs: phenelzine and tranylcypromine), triptans (sumatriptan), lithium, fentanyl, tramadol, and St. John’s wort can increase your risk for serotonin syndrome if taken together with mirtazapine.

Mirtazapine Warnings

  • Alcohol increases the nervous system side effects of mirtazapine.
  • Clinical worsening and suicide risk.
  • Agranulocytosis: In very rare cases agranulocytosis has been observed with mirtazapine treatment. If a patient develops a sore throat, fever, stomatitis, or other signs of infection along with a low WBC, treatment with mirtazapine should be discontinued and monitored. In the cases observed the agranulocytosis was reversed upon cessation.
  • Serotonin Syndrome: Mirtazapine should be avoided with other serotonin increasing drugs, and monitored closely in conjunction with SSRIs.
  • Angle-Closure Glaucoma: Mirtazapine should be carefully monitored in patients with angle-closure glaucoma, and in rare cases, mirtazapine could cause angle-closure glaucoma.
  • QT Prolongation and Torsades de Pointes: Caution should be exercised before starting this medication in patients with known heart disease, or family history of QT prolongation, and in concurrent use of other drugs believed to affect the QTc interval.
  • High Cholesterol: Mirtazapine may significantly elevate blood triglyceride and total cholesterol levels. Patients with preexisting high levels of fats in the blood should be monitored closely.

Dosage

Mirtazapine seems to be more sedating at lower doses and more activating at higher doses. In patients simply trying to treat insomnia, it is not unheard of to use 7.5 mg. The normal starting dosage is 15 to 30 mg and can be titrated up to a maximum dosage of 45 mg [RR].

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