Prescription Drug Information: Mirtazapine (Page 5 of 8)


Associated with Discontinuation of Treatment

Approximately 16% of the 453 patients who received mirtazapine tablets in US 6-week controlled clinical trials discontinued treatment due to an adverse experience, compared to 7% of the 361 placebo-treated patients in those studies. The most common events (≥1%) associated with discontinuation and considered to be drug related (i.e., those events associated with dropout at a rate at least twice that of placebo) are included in Table 2.

Table 2 : Common Adverse Events Associated with Discontinuation of Treatment in 6-week US Mirtazapine Tablets Trials
Adverse E vent Percentage of Patients Discontinuing with Adverse Even t
Mirtazapine Tablets (n=453 ) Placebo (n=3 61)
Somnolence 10.4% 2.2%
Nausea 1.5% 0%

Commonly Observed Adverse Events in US Controlled Clinical Trials

The most commonly observed adverse events associated with the use of mirtazapine tablets (incidence of 5% or greater) and not observed at an equivalent incidence among placebo-treated patients (mirtazapine tablets incidence at least twice that for placebo) are listed in Table 3.

Table 3: Common Treatment-emergent Adverse Events Associated with the Use of Mirtazapine Tablets in 6-week US Trials
Adverse Eve nt Percentage of Patients Reporting Adverse Even t
Mirtazapine Tablets (n=45 3) Placebo (n=3 61)
Somnolence 54% 18%
Increased Appetite 17% 2%
Weight Gain 12% 2%
Dizziness 7% 3%

Adverse Events Occurring at an Incidence of 1% or More Among Mirtazapine Tablet-treated Patients

Table 4 enumerates adverse events that occurred at an incidence of 1% or more, and were more frequent than in the placebo group, among mirtazapine tablet-treated patients who participated in short-term US placebo-controlled trials in which patients were dosed in a range of 5 to 60 mg/day. This table shows the percentage of patients in each group who had at least one episode of an event at some time during their treatment. Reported adverse events were classified using a standard COSTART-based dictionary terminology.

The prescriber should be aware that these figures cannot be used to predict the incidence of side effects in the course of usual medical practice where patient characteristics and other factors differ from those which prevailed in the clinical trials. Similarly, the cited frequencies cannot be compared with figures obtained from other investigations involving different treatments, uses, and investigators. The cited figures, however, do provide the prescribing physician with some basis for estimating the relative contribution of drug and nondrug factors to the side-effect incidence rate in the population studied.

Table 4: Incidence of Adverse Clinical Experiences * (≥ 1%) in Short-term US Controlled Studies
Body System Adverse Clinical Experience Mirtazapine Tablets (n=453) Placebo (n=361)
Body as a Whole
Asthenia 8% 5%
Flu Syndrome 5% 3%
Back Pain 2% 1%
Digestive System
Dry Mouth 25% 15%
Increased Appetite 17% 2%
Constipation 13% 7%
Metabolic and Nutritional Disorders
Weight Gain 12% 2%
Peripheral Edema 2% 1%
Edema 1% 0%
Musculoskeletal System
Myalgia 2% 1%
Nervous System
Somnolence 54% 18%
Dizziness 7% 3%
Abnormal Dreams 4% 1%
Thinking Abnormal 3% 1%
Tremor 2% 1%
Confusion 2% 0%
Respiratory System
Dyspnea 1% 0%
Urogenital System
Urinary Frequency 2% 1%

* Events reported by at least 1% of patients treated with mirtazapine tablets are included, except the following events, which had an incidence on placebo greater than or equal to mirtazapine tablets: headache, infection, pain, chest pain, palpitation, tachycardia, postural hypotension, nausea, dyspepsia, diarrhea, flatulence, insomnia, nervousness, libido decreased, hypertonia, pharyngitis, rhinitis, sweating, amblyopia, tinnitus, taste perversion.

ECG Changes

The electrocardiograms for 338 patients who received mirtazapine tablets and 261 patients who received placebo in 6-week, placebo-controlled trials were analyzed. Prolongation in QT c ≥500 msec was not observed among mirtazapine-treated patients; mean change in QT c was +1.6 msec for mirtazapine and -3.1 msec for placebo. Mirtazapine was associated with a mean increase in heart rate of 3.4 bpm, compared to 0.8 bpm for placebo. The clinical significance of these changes is unknown.

The effect of mirtazapine on QTc interval was assessed in a clinical randomized trial with placebo and positive (moxifloxacin) controls involving 54 healthy volunteers using exposure response analysis. This trial showed a positive relationship between mirtazapine concentrations and prolongation of the QTc interval. However, the degree of QT prolongation observed with both 45 mg (therapeutic) and 75 mg (supratherapeutic) doses of mirtazapine was not at a level generally considered to be clinically meaningful.

Other Adverse Events Observed During the Premarketing Evaluation of Mirtazapine Tablets

During its premarketing assessment, multiple doses of mirtazapine tablets were administered to 2796 patients in clinical studies. The conditions and duration of exposure to mirtazapine varied greatly, and included (in overlapping categories) open and double-blind studies, uncontrolled and controlled studies, inpatient and outpatient studies, fixed-dose and titration studies. Untoward events associated with this exposure were recorded by clinical investigators using terminology of their own choosing. Consequently, it is not possible to provide a meaningful estimate of the proportion of individuals experiencing adverse events without first grouping similar types of untoward events into a smaller number of standardized event categories.

In the tabulations that follow, reported adverse events were classified using a standard COSTART-based dictionary terminology. The frequencies presented, therefore, represent the proportion of the 2796 patients exposed to multiple doses of mirtazapine tablets who experienced an event of the type cited on at least one occasion while receiving mirtazapine tablets. All reported events are included except those already listed in Table 4, those adverse experiences subsumed under COSTART terms that are either overly general or excessively specific so as to be uninformative, and those events for which a drug cause was very remote.

It is important to emphasize that, although the events reported occurred during treatment with mirtazapine tablets, they were not necessarily caused by it.

Events are further categorized by body system and listed in order of decreasing frequency according to the following definitions: frequent adverse events are those occurring on one or more occasions in at least 1/100 patients; infrequent adverse events are those occurring in 1/100 to 1/1,000 patients; rare events are those occurring in fewer than 1/1,000 patients. Only those events not already listed in Table 4 appear in this listing. Events of major clinical importance are also described in the WARNINGS and PRECAUTIONS sections.

Body as a Whole

Frequent : malaise, abdominal pain, abdominal syndrome acute; infrequent: chills, fever, face edema, ulcer, photosensitivity reaction, neck rigidity, neck pain, abdomen enlarged; rare : cellulitis, chest pain substernal.

Cardiovascular System

Frequent : hypertension, vasodilatation; infrequent : angina pectoris, myocardial infarction, bradycardia, ventricular extrasystoles, syncope, migraine, hypotension; rare : atrial arrhythmia, bigeminy, vascular headache, pulmonary embolus, cerebral ischemia, cardiomegaly, phlebitis, left heart failure. provides trustworthy package insert and label information about marketed prescription drugs as submitted by manufacturers to the U.S. Food and Drug Administration. Package information is not reviewed or updated separately by Every individual prescription drug label and package insert entry contains a unique identifier which can be used to secure further details directly from the U.S. National Institutes of Health and/or the FDA.

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