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Klonopin (Clonazepam) - Side Effects and Adverse Reactions



The adverse experiences for Klonopin are provided separately for patients with seizure disorders and with panic disorder.

Seizure Disorders

The most frequently occurring side effects of Klonopin are referable to CNS depression. Experience in treatment of seizures has shown that drowsiness has occurred in approximately 50% of patients and ataxia in approximately 30%. In some cases, these may diminish with time; behavior problems have been noted in approximately 25% of patients. Others, listed by system, are:

Neurologic: Abnormal eye movements, aphonia, choreiform movements, coma, diplopia, dysarthria, dysdiadochokinesis, "glassy-eyed" appearance, headache, hemiparesis, hypotonia, nystagmus, respiratory depression, slurred speech, tremor, vertigo

Psychiatric: Confusion, depression, amnesia, hallucinations, hysteria, increased libido, insomnia, psychosis (the behavior effects are more likely to occur in patients with a history of psychiatric disturbances). The following paradoxical reactions have been observed: excitability, irritability, aggressive behavior, agitation, nervousness, hostility, anxiety, sleep disturbances, nightmares and vivid dreams

Respiratory: Chest congestion, rhinorrhea, shortness of breath, hypersecretion in upper respiratory passages

Cardiovascular: Palpitations

Dermatologic: Hair loss, hirsutism, skin rash, ankle and facial edema

Gastrointestinal: Anorexia, coated tongue, constipation, diarrhea, dry mouth, encopresis, gastritis, increased appetite, nausea, sore gums

Genitourinary: Dysuria, enuresis, nocturia, urinary retention

Musculoskeletal: Muscle weakness, pains

Miscellaneous: Dehydration, general deterioration, fever, lymphadenopathy, weight loss or gain

Hematopoietic: Anemia, leukopenia, thrombocytopenia, eosinophilia

Hepatic: Hepatomegaly, transient elevations of serum transaminases and alkaline phosphatase

Panic Disorder

Adverse events during exposure to Klonopin were obtained by spontaneous report and 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 events into a smaller number of standardized event categories. In the tables and tabulations that follow, CIGY dictionary terminology has been used to classify reported adverse events, except in certain cases in which redundant terms were collapsed into more meaningful terms, as noted below.

The stated frequencies of adverse events represent the proportion of individuals who experienced, at least once, a treatment-emergent adverse event of the type listed. An event was considered treatment-emergent if it occurred for the first time or worsened while receiving therapy following baseline evaluation.

Adverse Findings Observed in Short-Term, Placebo-Controlled Trials

Adverse Events Associated With Discontinuation of Treatment

Overall, the incidence of discontinuation due to adverse events was 17% in Klonopin compared to 9% for placebo in the combined data of two 6- to 9-week trials. The most common events (≥1%) associated with discontinuation and a dropout rate twice or greater for Klonopin than that of placebo included the following:

Table 2 Most Common Adverse Events (≥1%) Associated with Discontinuation of Treatment
Adverse Event Klonopin (N=574) Placebo (N=294)
Somnolence 7% 1%
Depression 4% 1%
Dizziness 1% <1%
Nervousness 1% 0%
Ataxia 1% 0%
Intellectual Ability Reduced 1% 0%

Adverse Events Occurring at an Incidence of 1% or More Among Klonopin-Treated Patients

Table 3 enumerates the incidence, rounded to the nearest percent, of treatment-emergent adverse events that occurred during acute therapy of panic disorder from a pool of two 6- to 9-week trials. Events reported in 1% or more of patients treated with Klonopin (doses ranging from 0.5 to 4 mg/day) and for which the incidence was greater than that in placebo-treated patients are included.

The prescriber should be aware that the figures in Table 3 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 that prevailed in the clinical trials. Similarly, the cited frequencies cannot be compared with figures obtained from other clinical 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 in the population studied.

Table 3 Treatment-Emergent Adverse Event Incidence in 6- to 9-Week Placebo-Controlled Clinical TrialsEvents reported by at least 1% of patients treated with Klonopin and for which the incidence was greater than that for placebo.
Clonazepam Maximum Daily Dose
Adverse Event
by Body System
All Klonopin Groups
Central & Peripheral Nervous System
  Somnolence 1 26 35 50 36 37 10
  Dizziness 5 5 12 8 8 4
  Coordination Abnormal 1 2 7 9 6 0
  Ataxia 2 1 8 8 5 0
  Dysarthria 0 0 4 3 2 0
  Depression 7 6 8 8 7 1
  Memory Disturbance 2 5 2 5 4 2
  Nervousness 1 4 3 4 3 2
  Intellectual Ability Reduced 0 2 4 3 2 0
  Emotional Lability 0 1 2 2 1 1
  Libido Decreased 0 1 3 1 1 0
  Confusion 0 2 2 1 1 0
Respiratory System
  Upper Respiratory Tract Infection 10 10 7 6 8 4
  Sinusitis 4 2 8 4 4 3
  Rhinitis 3 2 4 2 2 1
  Coughing 2 2 4 0 2 0
  Pharyngitis 1 1 3 2 2 1
  Bronchitis 1 0 2 2 1 1
Gastrointestinal System
  Constipation 0 1 5 3 2 2
  Appetite Decreased 1 1 0 3 1 1
  Abdominal Pain 2 2 2 0 1 1
Body as a Whole
  Fatigue 9 6 7 7 7 4
  Allergic Reaction 3 1 4 2 2 1
  Myalgia 2 1 4 0 1 1
Resistance Mechanism Disorders
  Influenza 3 2 5 5 4 3
Urinary System
  Micturition Frequency 1 2 2 1 1 0
  Urinary Tract Infection 0 0 2 2 1 0
Vision Disorders
  Blurred Vision 1 2 3 0 1 1
Reproductive DisordersDenominators for events in gender-specific systems are: n=240 (clonazepam), 102 (placebo) for male, and 334 (clonazepam), 192 (placebo) for female.
  Dysmenorrhea 0 6 5 2 3 2
  Colpitis 4 0 2 1 1 1
  Ejaculation Delayed 0 0 2 2 1 0
  Impotence 3 0 2 1 1 0

1 Indicates that the p-value for the dose-trend test (Cochran-Mantel-Haenszel) for adverse event incidence was ≤0.10.

Commonly Observed Adverse Events

Table 4 Incidence of Most Commonly Observed Adverse EventsTreatment-emergent events for which the incidence in the clonazepam patients was ≥5% and at least twice that in the placebo patients. in Acute Therapy in Pool of 6- to 9-Week Trials
Adverse Event
(Genentech Preferred Term)
Somnolence 37% 10%
Depression 7% 1%
Coordination Abnormal 6% 0%
Ataxia 5% 0%

Treatment-Emergent Depressive Symptoms

In the pool of two short-term placebo-controlled trials, adverse events classified under the preferred term "depression" were reported in 7% of Klonopin-treated patients compared to 1% of placebo-treated patients, without any clear pattern of dose relatedness. In these same trials, adverse events classified under the preferred term "depression" were reported as leading to discontinuation in 4% of Klonopin-treated patients compared to 1% of placebo-treated patients. While these findings are noteworthy, Hamilton Depression Rating Scale (HAM-D) data collected in these trials revealed a larger decline in HAM-D scores in the clonazepam group than the placebo group suggesting that clonazepam-treated patients were not experiencing a worsening or emergence of clinical depression.

Other Adverse Events Observed During the Premarketing Evaluation of Klonopin in Panic Disorder

Following is a list of modified CIGY terms that reflect treatment-emergent adverse events reported by patients treated with Klonopin at multiple doses during clinical trials. All reported events are included except those already listed in Table 3 or elsewhere in labeling, those events for which a drug cause was remote, those event terms which were so general as to be uninformative, and events reported only once and which did not have a substantial probability of being acutely life-threatening. It is important to emphasize that, although the events occurred during treatment with Klonopin, they were not necessarily caused by it.

Events are further categorized by body system and listed in order of decreasing frequency. These adverse events were reported infrequently, which is defined as occurring in 1/100 to 1/1000 patients.

Body as a Whole: weight increase, accident, weight decrease, wound, edema, fever, shivering, abrasions, ankle edema, edema foot, edema periorbital, injury, malaise, pain, cellulitis, inflammation localized

Cardiovascular Disorders: chest pain, hypotension postural

Central and Peripheral Nervous System Disorders: migraine, paresthesia, drunkenness, feeling of enuresis, paresis, tremor, burning skin, falling, head fullness, hoarseness, hyperactivity, hypoesthesia, tongue thick, twitching

Gastrointestinal System Disorders: abdominal discomfort, gastrointestinal inflammation, stomach upset, toothache, flatulence, pyrosis, saliva increased, tooth disorder, bowel movements frequent, pain pelvic, dyspepsia, hemorrhoids

Hearing and Vestibular Disorders: vertigo, otitis, earache, motion sickness

Heart Rate and Rhythm Disorders: palpitation

Metabolic and Nutritional Disorders: thirst, gout

Musculoskeletal System Disorders: back pain, fracture traumatic, sprains and strains, pain leg, pain nape, cramps muscle, cramps leg, pain ankle, pain shoulder, tendinitis, arthralgia, hypertonia, lumbago, pain feet, pain jaw, pain knee, swelling knee

Platelet, Bleeding and Clotting Disorders: bleeding dermal

Psychiatric Disorders: insomnia, organic disinhibition, anxiety, depersonalization, dreaming excessive, libido loss, appetite increased, libido increased, reactions decreased, aggressive reaction, apathy, attention lack, excitement, feeling mad, hunger abnormal, illusion, nightmares, sleep disorder, suicide ideation, yawning

Reproductive Disorders, Female: breast pain, menstrual irregularity

Reproductive Disorders, Male: ejaculation decreased

Resistance Mechanism Disorders: infection mycotic, infection viral, infection streptococcal, herpes simplex infection, infectious mononucleosis, moniliasis

Respiratory System Disorders: sneezing excessive, asthmatic attack, dyspnea, nosebleed, pneumonia, pleurisy

Skin and Appendages Disorders: acne flare, alopecia, xeroderma, dermatitis contact, flushing, pruritus, pustular reaction, skin burns, skin disorder

Special Senses Other, Disorders: taste loss

Urinary System Disorders: dysuria, cystitis, polyuria, urinary incontinence, bladder dysfunction, urinary retention, urinary tract bleeding, urine discoloration

Vascular (Extracardiac) Disorders: thrombophlebitis leg

Vision Disorders: eye irritation, visual disturbance, diplopia, eye twitching, styes, visual field defect, xerophthalmia


Below is a sample of reports where side effects / adverse reactions may be related to Klonopin. The information is not vetted and should not be considered as verified clinical evidence.

Possible Klonopin side effects / adverse reactions in 33 year old female

Reported by a consumer/non-health professional from United States on 2011-10-03

Patient: 33 year old female

Reactions: Hypersensitivity, Urinary Incontinence, Faecal Incontinence, Mental Disorder, Disturbance in Attention, Amnesia

Adverse event resulted in: hospitalization

Suspect drug(s):
    Dosage: unknown dosing details
    Indication: Product Used FOR Unknown Indication

    Dosage: suboxone sublingual film. dosage unknown.
    Indication: Product Used FOR Unknown Indication

Possible Klonopin side effects / adverse reactions in 30 year old male

Reported by a consumer/non-health professional from United States on 2011-10-05

Patient: 30 year old male

Reactions: Weight Decreased, Eye Infection, Drug Abuse, Loss of Consciousness, OFF Label USE, Glycosylated Haemoglobin Increased, Blood Glucose Increased, Fluid Retention, Pneumonia, Ear Infection, Condition Aggravated, Dysgeusia, Activities of Daily Living Impaired, Memory Impairment, Feeling Abnormal, Infection

Suspect drug(s):
    Administration route: Oral
    Indication: Panic Disorder

    Dosage: sublingual film; 12 mg alternates with 10mg every other day
    Indication: Drug Dependence
    Start date: 2011-04-01

Multiple Benzodiazepines
    Dosage: unit dose varied; high doses every hour or two
    Indication: Dependence
    Start date: 2011-05-01
    End date: 2011-06-01

Other drugs received by patient: Prozac; Regular Insulin; Lantus

Possible Klonopin side effects / adverse reactions in 29 year old female

Reported by a consumer/non-health professional from United States on 2011-10-05

Patient: 29 year old female

Reactions: Hyperventilation, OFF Label USE, Weight Decreased, Fatigue, Diarrhoea, Hyperhidrosis, Loss of Consciousness, Substance Abuse

Suspect drug(s):
    Administration route: Oral
    Indication: Sleep Disorder
    End date: 2011-08-01

    Indication: Pain
    Start date: 2011-01-01
    End date: 2011-08-01

    Dosage: suboxone film strips
    Indication: Pain
    Start date: 2011-08-01

Other drugs received by patient: Cymbalta; Adderall 5

See index of all Klonopin side effect reports >>

Drug label data at the top of this Page last updated: 2013-12-12

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