Mirtazapine dosage, forms, and strengths

Mirtazapine (Remeron, Remeron Soltab) is a unique antidepressant. It is classified as a tetracyclic antidepressant, a rare classification but one that is similar to the more common tricyclic antidepressant class. Prescriptions of mirtazapine are typically for major depression treatment. The medicine is also used off-label for anxiety treatment and prevention of tension headaches.

RELATED: What is mirtazapine?

Mirtazapine forms and strengths

• Mirtazapine tablets: 7.5 mg, 15 mg, 30 mg, 45 mg

• Mirtazapine ODT (orally disintegrating tablets): 15 mg, 30 mg, 45 mg

Mirtazapine dosage for adults

Mirtazapine is indicated by the FDA for the treatment of major depressive disorder. Major depression is a diagnosis that requires certain criteria for symptoms, severity, and duration. Other depressive disorders, besides major depression, are treated off-label (without an FDA-approved indication) with mirtazapine at times.

Mirtazapine dosage for major depressive disorder

Mirtazapine’s mechanism of action for treating depression is not fully understood, but it is known to antagonize or block certain adrenergic and serotonin receptors in the brain. This likely permits greater activity of other, unblocked adrenergic and serotonin receptors and thereby produces the intended effects on mood.

Interestingly, mirtazapine is often chosen for its side effects, which may be desirable in certain circumstances. Mirtazapine is known to cause drowsiness in 23% of individuals and sedation in 19%, likely related to its stimulation of histamine receptors. By inducing somnolence, it may assist those having insomnia. Appetite stimulation and weight gain can also be experienced with the drug. In fact, 11% of people taking mirtazapine may experience an increase in appetite. Accordingly, individuals experiencing a loss of appetite may benefit from this side effect.

The starting dosage of mirtazapine is typically 15 mg once daily, but there are instances, such as in seniors, when the starting dose of 7.5 mg is preferred. The dosing can be gradually increased to higher doses every two to four weeks up to a maximum of 45 mg daily. In more urgent situations, the dose increases can be made on a weekly basis.

If Remeron Soltab (the mirtazapine ODT form) is chosen, these dissolvable tablets are placed on the tongue and allowed to disintegrate rather than being chewed. They are an appropriate choice for someone with swallowing difficulties.

Mirtazapine dosage for children

Although off-label prescribing for children occurs, mirtazapine is not FDA-approved for use in the pediatric population.

Mirtazapine dosage restrictions

In the setting of renal impairment (reduced kidney function) or hepatic impairment (reduced liver function), specific dosing changes are not defined. However, lower starting and maximum doses of mirtazapine are usually recommended for anyone with advanced renal or hepatic impairment.

Close monitoring of mirtazapine usage and dosage is recommended in certain medical conditions: 

• Suicidal thoughts may increase in the short term after starting mirtazapine or other antidepressants, particularly in children and young adults, to a degree that the FDA placed a black box warning on antidepressants about this effect. 

• A history of glaucoma may warrant follow-up of ocular pressure while on the drug.

• Additionally, any sign of anemia or bleeding should be brought to medical attention as mirtazapine has been associated with blood cell dyscrasia (drops in blood cell counts). Specifically a drop in immune cells, termed agranulocytosis, could manifest as an increase in infections. 

• As with other antidepressants, anyone with a history of bipolar disorder should be monitored for mania or hypomania when starting mirtazapine. 

Mirtazapine contraindications (times when it should not be used) include:

• Anyone with a history of hypersensitivity or allergic reaction to it. 

• Anyone who has used monoamine oxidase inhibitors (MAOIs), including linezolid or methylene blue, in the past 14 days should not take mirtazapine.

Mirtazapine dosage for pets

Mirataz (mirtazapine) is a topical ointment, which is FDA-approved for use in cats to stimulate appetite and induce weight gain. A 1.5-inch ribbon of ointment is applied daily inside the cat’s ear.

How to take mirtazapine

Following dosing and timing recommendation is particularly important for this antidepressant. Taking mirtazapine in the evening typically works best, owing to its potential for sedation. Any dose increase or decrease should be done under the direction of a healthcare professional. The list below reviews other important treatment elements to consider.

• Take your medicine as directed. Your dose may need to be changed several times to find what works best for you. Your doctor may tell you to take this medicine at bedtime because it can make you sleepy.

• You may need to take this medicine for several weeks before you begin to feel better.

• Make sure your hands are dry before you handle the disintegrating tablet. Peel back the foil from the blister pack, then remove the tablet. Do not push the tablet through the foil. Place the tablet in your mouth. After it has melted, swallow or take a drink of water. Do not crush, split, or break the tablet.

• This medicine should come with a medication guide. Ask your pharmacist for a copy if you do not have one.

• Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep the orally disintegrating tablet in the original package until you are ready to take it.

Mirtazapine dosage FAQs

Remeron vs. Remeron Soltab: What’s the difference?

Remeron and Remeron Soltab are dosed the same and used for the same conditions. Remeron is the brand-name swallowable tablet of mirtazapine, while Remeron Soltab is the brand-name ODT (dissolvable) tablet of mirtazapine.

How long does it take mirtazapine to work?

Like many antidepressants, mirtazapine takes time to be effective. Depressed patients may notice an improvement in mood or motivation within the first week, but many will not notice a benefit for two to four weeks. A dose increase may even be needed in order to experience relief of symptoms. The effects of mirtazapine may continue to increase and not plateau for six weeks after initiation or increase of the medication. 

How long does mirtazapine stay in your system?

The half-life of mirtazapine is 20 to 40 hours, although this may be affected by kidney or liver function. This means that it can take 40 hours for the body to reduce the plasma concentration of the drug in half. It also means that bodily elimination of 97% of the drug can take more than eight days.

What happens if I miss a dose of mirtazapine?

A missed dose of mirtazapine typically should be taken as soon as possible when remembered, but if it is nearly time for the next dose, then the missed dose should be skipped in favor of waiting for the regular dose. The pharmacokinetics of mirtazapine are such that its effects will not immediately wear off. Doubling up doses to make up for a missed dose should not be done.

How long can you take mirtazapine?

Based on clinical trials with other antidepressants, mirtazapine may be prescribed indefinitely if it continues to be required as a maintenance treatment of depression. For initial, nonsevere episodes of depression, treatment may be discontinued in less than a year upon the recommendation of the healthcare provider.

How do I stop taking mirtazapine?

Before stopping mirtazapine, a consultation with the prescribing healthcare professional is required. If a mutual decision is made to stop the medication, a gradual taper off the drug will likely be recommended. Abrupt discontinuation of mirtazapine can lead to withdrawal symptoms, like anxiety, nausea, dizziness, skin tingling, and insomnia.

What is the maximum dosage for mirtazapine?

The maximum FDA-approved dosage of mirtazapine is 45 mg once daily. In those with advanced renal or hepatic impairment, lowering the maximum dosage to 30 mg daily may be best.

Can you overdose on mirtazapine?

An overdose of mirtazapine may cause adverse reactions including drowsiness, confusion, memory loss, or tachycardia (fast heart rate), but the more serious concern is a rare effect on the heart rhythm. Prolongation of the QT interval, torsades de pointes, ventricular tachycardia or fibrillation, sudden death, and cardiac arrest have all been reported with mirtazapine overdose.

What interacts with mirtazapine?

Lack of potent p450 liver enzyme activity leaves mirtazapine with fewer drug interactions than many other medications. The drug is neither a potent p450 inducer nor inhibitor. Nonetheless, there are some notable medications that should be avoided or at least discussed specifically with the healthcare professional.

The list of contraindicated drugs to be avoided in combination with mirtazapine includes:

• Isocarboxazid

• Linezolid

• Methylene blue

• Phenelzine

• Pimozide

• Safinamide

• Selegiline transdermal

• Thioridazine

• Tranylcypromine

A more extensive list of medications warrants caution before taking concurrently with mirtazapine. The list includes:

• Cimetidine

• Diazepam

• St. John's Wort

• Tramadol

• Tryptophan

• Certain antibiotics like clarithromycin and rifampin

• Some antifungals such as ketoconazole and itraconazole

• Certain antivirals against HIV

• Certain migraine medications like sumatriptan

• Certain seizures medications like carbamazepine and phenytoin

• Other antidepressants like paroxetine and other SSRIs, mood stabilizers like lithium, and even antipsychotics can interact with mirtazapine

One commonality amongst many of the drugs on the lists above is the potential for the increased risk of serotonin syndrome. Since mirtazapine affects serotonin action, individuals can experience serotonin syndrome when two or more medications with serotonergic activity are taken together. Symptoms of serotonin syndrome can consist of dry mouth, sweating, tremor, muscle spasm, agitation, and rigidity.

What happens when you mix mirtazapine and alcohol?

Drinking alcohol when taking mirtazapine can increase the risk for serious side effects like dangerous degrees of drowsiness and sedation. The amount of alcohol that produces this effect will vary from person to person and may depend on the dose of mirtazapine. Accordingly, it is likely best to avoid alcohol while taking mirtazapine.

Is it safe to take mirtazapine during pregnancy?

Mirtazapine is not usually the first-line medication for depression during pregnancy, and study data on mirtazapine use during pregnancy is limited. The data that is available indicates that mirtazapine can be used during pregnancy if needed, partly because treatment of depression in pregnancy can be quite beneficial. Newborns born to mothers taking mirtazapine may experience temporary withdrawal symptoms. 

After delivery, breastfeeding is considered safe, based on limited study data, for mothers being treated with mirtazapine. The medication and its metabolite are detectable in breast milk.

Related resources for mirtazapine dosages:

• Mirtazapine: a review of its use in major depression and other psychiatric disorders, CNS Drugs

• Safety of mirtazapine, International Clinical Psychopharmacology

• Adult dosing, Epocrates

• Contraindications, Epocrates

• Drug interactions, Epocrates

• Mirtazapine drug information, FDA

• Helping our cats live healthier lives, FDA

• Remeron RD product monograph, Merck

• Five-year outcome for maintenance therapies in recurrent depression, Archives of General Psychiatry

• Review of maintenance trials for major depressive disorder, The Journal of Clinical Psychiatry

• Mirtazapine withdrawal symptoms, The Canadian Journal of Psychiatry

• Transfer of the antidepressant mirtazapine into breast milk, British Journal of Clinical Pharmacology