Mirtazapine: Formula, Presentation, Indications, Action Mechanism, Dosage, Side Effects, Warnings and Interactions

It is an antidepressant that works by restoring the balance of natural chemicals (neurotransmitters) in the brain.

Mirtazapine is a drug that is intended for the treatment of depression.

This medicine improves mood and the feeling of well-being.

This compound is used to combat depressive states, influencing the increase of some activities in the brain to achieve mental balance in the patient.

Chemical formula

  • C17H19N3.


  • Mirtazapine is packaged in the form of regular tablets and 30 mg soluble tablets for oral use.


Mirtazapine is used to treat the major depressive disorder.

It is also commonly used in the geriatric population.

This age group is used to combat insomnia that causes a decrease in body weight; this treatment can benefit this group of patients with sedation and an induced weight gain.


Mechanism of action

An essential characteristic of its mechanism of action is its effect as an antagonist of histamine 1.

This antihistamine effect is related to sedation and weight gain.


An initial dose of 15 or 30 mg per day is recommended. Then depending on the response of the patient, the dose can be increased, by medical recommendation, after a few days of treatment at doses between 15 and 45 mg per day.

Usually, the recommended dose is the same for all ages. Still, in the case of geriatric patients who suffer from kidney or liver diseases, the doctor can modify the amount.

This medication is recommended for oral use, accompanied or not with food, once a day at bedtime.

The dosage will depend on the condition and the response to treatment by the patient, but doses greater than 45 mg per day should not be administered.

This medication should be used regularly to get the most benefit. Also, it should be used at the same time every day.

To begin to notice the improvement of symptoms, one should wait for one to four weeks, so the dose should not be increased or taken more frequently than prescribed by the doctor.

It is essential to continue taking this medication even if the patient feels well.

Do not stop taking this medication without consulting your doctor, as some conditions may worsen when the medication stops abruptly, causing unpleasant withdrawal symptoms.

The dose may need to be decreased gradually.

Within the indications for the use of the oral disintegration tablets of mirtazapine, the following are observed:

  • The tablet should be kept in your blister pack until you are ready to take the medication. The package should be opened and the foil removed from the tablet. Do not push a tablet through the foil, or you can break the tablet.
  • The hands must be dry; when drawing the tablet, it is placed in the mouth, and it will begin to dissolve immediately.
  • The entire tablet should never be swallowed. It should be allowed to dissolve in the mouth without chewing it.
  • Swallow the content as it dissolves in the mouth; it is not necessary to drink water.

Side effects

You should seek medical attention immediately if you have any of the symptoms associated with an allergic reaction, such as rashes or hives, difficulty breathing, or swelling of the face, lips, tongue, or throat.

Serious side effects may occur, such as:

  • Presence of agitation, hallucinations, rapid heart rate, hyperactive reflexes, nausea, vomiting, diarrhea, and loss of coordination.
  • Effects include muscle stiffness, high fever, sweating, confusion, rapid or uneven heartbeat, and tremors.
  • Fainting.
  • Febrile symptoms, chills, body aches, flu symptoms.
  • The appearance of white patches or sores inside the mouth or on the lips.
  • Headaches, difficulty concentrating, memory problems, weakness, or emotional instability.

Less serious side effects include:

  • Drowsiness, dizziness.
  • Increased appetite
  • Weight gain.

It is also possible that symptoms appear such as mood or behavior changes, anxiety pictures, panic attacks, insomnia problems, impulsivity, irritability, agitation, hostility, aggression, and restlessness.

Mental or physical hyperactivity increases depression, suicidal thoughts, or hurting yourself.

In these cases, you should see the doctor immediately.

Warnings and contraindications

If the patient is under 24 years of age, he may have suicidal thoughts when he starts taking an antidepressant.

If it is necessary to administer it, you should have regular control during the first 12 weeks of treatment.

Close family members or caregivers should be alert to changes in mood or any new symptoms that appear during treatment administration.

This medication should not be administered if the patient is allergic to mirtazapine.

Also, if you are taking tryptophan (L-tryptophan).

Before taking mirtazapine, you should inform the doctor if you have bipolar disorder, liver or kidney disease, seizures, or heart disease.

As well as a history of heart attack or stroke, or a history of drug abuse or suicidal thoughts.

The action of this medication can take up to several weeks.

Even if your symptoms do not improve, you should continue to use the medication as directed by the doctor and inform the doctor if the symptoms still do not improve after four weeks of treatment.

Alcohol consumption is contraindicated because it can potentiate some side effects of mirtazapine.

Mirtazapine can cause drowsiness, so you must be very careful if you drive a vehicle or operate some machinery or equipment that requires the patient to be alert.

Mirtazapine should not be used if treatment has been continued for the past 14 days with a monoamine or monoamine oxidase inhibitor, such as:

La furazolidona (Furoxone), la isocarboxazida (Marplan), la fenelzina (Nardil), la rasagilina (Azilect), la selegilina (Eldepryl o Emsam) o el tranylcypromine (Parnate).

Serious and life-threatening side effects can occur if mirtazapine is used before the monoamine oxidase inhibitor has disappeared from the body.

To safely use mirtazapine, you should inform your doctor if you have any of these conditions:

  • If you have liver or kidney disease.
  • If you have bipolar disorder or manic depression.
  • If you suffer from seizures or epilepsy.
  • Problems of arterial hypotension or dizziness.
  • Issues with high cholesterol or triglycerides.
  • Heart diseases, including angina.
  • The present history of heart attack or stroke.
  • The current record of drug abuse or suicidal thoughts.

This medication is listed as Category C in pregnancy by the Food and Drug Administration.

It is still not known truthfully if mirtazapine can cause harm to the unborn baby.

The doctor should be informed if you are pregnant or if you plan to become pregnant while using this medication.

It is not yet known if mirtazapine passes into breast milk or if it could harm a baby while you are breastfeeding.

This medicine should not be used if you are breastfeeding a baby, so you should stop breastfeeding while under treatment.

The tablet dissolved orally may contain phenylalanine, so it should not be given if you have phenylketonuria (PKU). This genetic disorder does not allow the body to process part of phenylalanine protein.


Specific side effects of mirtazapine may increase with alcohol consumption.

Medications used for colds or allergies, sedatives, narcotic analgesics, sleeping pills, muscle relaxers, and medicines for seizures or anxiety can cause an increase in sleepiness that commonly causes mirtazapine.

Therefore, the doctor should be informed if these medications are used regularly.

Many drugs can interact with mirtazapine. The doctor should be informed if any of these medications are being used:

  • Cimetidine (Tagamet).
  • El conivaptan (Vaprisol).
  • El imatinib (Gleevec).
  • Isoniazid (to treat tuberculosis).
  • El litio (Eskalith, LithoBid).
  • The Grass of San Juan.
  • El tramadol (Ultram, Ultracet).
  • Anticoagulants such as warfarin (Coumadin, Jantoven).
  • Some antibiotics such as clarithromycin (Biaxin), erythromycin (EES, EryPed, Ery-Tab, Erythrocin, Pediazole), and rifampin (Rifadin, Rifatter, Rifamate) or telithromycin (Ketek).
  • Antidepressants such as amitriptyline (Elavil, Vanatrip, Limbitrol), citalopram (Celexa), doxepin (Sinequan), desipramine (Norpramin), desvenlafaxine (Pristiq), fluoxetine (Prozac, Rapiflux, Sarafem, Selfemra, Symbyax), imipramine (Janimine, Tofranil), nefazodone, etc.
  • Antifungal medications such as itraconazole (Sporanox), ketoconazole (Nizoral) or miconazole (Oravig).
  • Some heart or blood pressure medicines include nicardipine (Cardene) or quinidine (Quin-G).
  • Drugs for HIV / AIDS such as atazanavir (Reyataz), delavirdine (Rescriptor), indinavir (Crixivan), nelfinavir (Viracept), saquinavir (Invirase) or ritonavir (Norvir, Kaletra).
  • Medications for migraine such as almotriptan (Axert), eletriptan (Relpax), frovatriptan (Frova), naratriptan (Amerge), rizatriptan (Maxalt), sumatriptan (Imitrex) or zolmitriptan (Zomig).
  • Medications for seizures include carbamazepine (Carbatrol, Equetro, Tegretol) or phenytoin (Dilantin).