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Mirtazapine Side Effects

Commonly reported side effects of mirtazapine include severe sedation, increased serum cholesterol, drowsiness, constipation, weight gain, insomnia, fatigue, increased appetite, xerostomia, and decreased appetite. Other side effects include increased serum triglycerides, dizziness, tremor, vertigo, hot flash, palpitations, dyspepsia, abnormal dreams, bitter taste, decreased libido, and diaphoresis. See below for a comprehensive list of adverse effects.

For the Consumer

Applies to mirtazapine: oral tablet, oral tablet disintegrating

In addition to its needed effects, some unwanted effects may be caused by mirtazapine. In the event that any of these side effects do occur, they may require medical attention.

You should check with your doctor immediately if any of these side effects occur when taking mirtazapine:

Less common
  • Decreased or increased movement
  • mood or mental changes, including abnormal thinking, agitation, anxiety, confusion, and feelings of not caring
  • shortness of breath
  • skin rash
  • swelling
  • Change in menstrual cycle (periods)
  • convulsions (seizures)
  • decreased sexual ability
  • menstrual pain
  • mood or mental changes, including anger, feelings of being outside the body, hallucinations (seeing, hearing, or feeling things that are not there), mood swings, and unusual excitement
  • mouth sores
  • sore throat, chills, or fever

Some of the side effects that can occur with mirtazapine may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common
  • Constipation
  • dizziness
  • drowsiness
  • dry mouth
  • increased appetite
  • weight gain
Less common
  • Abdominal or stomach pain
  • abnormal dreams
  • back pain
  • dizziness or fainting when getting up suddenly from a lying or sitting position
  • increased need to urinate
  • increased sensitivity to touch
  • increased thirst
  • low blood pressure
  • muscle pain
  • nausea
  • sense of constant movement of self or surroundings
  • trembling or shaking
  • vomiting
  • weakness

For Healthcare Professionals

Applies to mirtazapine: oral tablet, oral tablet disintegrating

Nervous system

Although the exact incidence has not been reported, paresthesia appears to be a relatively common side effect of mirtazapine. Patients typically experience paresthesia in the extremities or generalized in the body. However, several cases of oral paresthesia associated with the orally disintegrating tablet have been reported. Patients have described a sensation of swelling in the mouth, numbness, and anesthesia. The symptoms occur shortly after ingestion and resolve after a few hours.

Nearly all selective serotonin reuptake inhibitors, mixed serotonin/norepinephrine reuptake inhibitors, and tricyclic antidepressants cause sleep abnormalities to some extent. These antidepressants have marked dose-dependent effects on rapid eye movement (REM) sleep, causing reductions in the overall amount of REM sleep over the night and delays the first entry into REM sleep (increased REM sleep onset latency (ROL)), both in healthy subjects and depressed patients. The antidepressants that increase serotonin function appear to have the greatest effect on REM sleep. The reduction in REM sleep is greatest early in treatment, but gradually returns towards baseline during long-term therapy; however, ROL remains long. Following discontinuation of therapy the amount of REM sleep tends to rebound. Some of these drugs (i.e., bupropion, mirtazapine, nefazodone, trazodone, trimipramine) appear to have a modest or minimal effect on REM sleep.[Ref]

Nervous system side effects including somnolence (56%), headache (12%), dizziness (7% to 12%), insomnia (8%), abnormal dreams (4%), abnormal thinking (3%), confusion (2%), tremor (2%), sleep abnormalities, and paresthesia have been reported. Activation of mania and seizures have occurred rarely. One case of seizures, one case of akathisia, and one patient with a transient ischemic attack have also been reported.[Ref]


Gastrointestinal side effects including dry mouth (25%), increased appetite (17%), and constipation (13%) have been reported. Other reported gastrointestinal adverse effects have included diarrhea (9%), nausea (4%), vomiting, anorexia, cholecystitis, glossitis, and colitis. One case of subclinical pancreatitis has also been reported.[Ref]


Metabolic side effects have been reported. Nonfasting triglyceride increases to greater than 20% above the normal upper limits have been reported in 15% of patients receiving mirtazapine in clinical trials. Weight gain has been reported in 12% of patients. Less frequently reported were peripheral edema (2%), thirst, and weight loss. In one small study, mirtazapine appeared to improve glucose tolerance by reducing cortisol secretion.[Ref]


Numerous cases of mirtazapine- induced arthralgia have been reported. Symptoms tend to appear within 2 to 22 days of starting mirtazapine and resolve shortly after discontinuation of treatment.[Ref]

Musculoskeletal side effects including myalgia, arthralgia (2.4%), and myasthenia have been reported in less than 2% of patients receiving mirtazapine.[Ref]


Hepatic side effects including liver function test abnormalities (primarily ALT (SGPT) elevations greater than three times normal concentrations) have been reported in 2% of patients receiving mirtazapine. Patients typically did not develop signs or symptoms of hepatic dysfunction[Ref]

A case of mirtazapine- associated, dose-dependent asymptomatic elevation of liver enzymes has been reported. In this patient, elevated liver enzymes were discovered 3 months after starting mirtazapine (30 mg/day) and following a dose reduction (15 mg/day) liver enzymes decreased, but remained above normal. Liver enzymes returned to normal 2 months after discontinuation of mirtazapine.[Ref]


Respiratory side effects including dyspnea (1%) have been reported.[Ref]


Tachycardia, palpitation, chest pain, and postural hypotension were reported by at least 1% of patients in clinical trials, however, the incidence was less than that of placebo. ECG changes were also noted in 3% of patients. The incidence was similar to that of placebo and the changes were not considered clinically significant.[Ref]

Cardiovascular side effects including hypertension, vasodilation, angina pectoris, bradycardia, and ventricular extrasystoles have been reported infrequently.[Ref]


Hematologic and lymphatic side effects such as lymphadenopathy, leukopenia, anemia, petechiae, thrombocytopenia, lymphocytosis, and pancytopenia have been reported but are uncommon. Agranulocytosis occurred in two patients and neutropenia in one patient during premarketing clinical trials. One case of coagulopathy has been reported.[Ref]

Coagulopathy (i.e., ecchymosis) developed in a patient three days after initiating mirtazapine therapy (30 mg/day). Following discontinuation of mirtazapine, prothrombin time, activated partial thromboplastin time, and international normalized ratio returned to normal and symptoms of ecchymosis disappeared.[Ref]


Dermatologic side effects including pruritus, rash, acne, dry skin, and alopecia have been reported infrequently. Postmarketing cases of severe skin reactions, including Stevens-Johnson Syndrome, bullous dermatitis, erythema multiforme and toxic epidermal necrolysis have also been reported.[Ref]


General side effects have included asthenia (8%), flu syndrome (5%), and back pain (2%).[Ref]


Ocular side effects including eye pain, abnormality of accommodation, conjunctivitis, lacrimation, and glaucoma have been reported infrequently. A case of palinopsia has also been recorded.[Ref]


Genitourinary side effects including urinary frequency (2%), urinary tract infection, kidney calculus, cystitis, urinary incontinence, vaginitis, hematuria, impotence, and polyuria have been reported.[Ref]


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Not all side effects for mirtazapine may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

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