Note: This document contains side effect information about clonazepam. Some of the dosage forms listed on this page may not apply to the brand name Klonopin.

Common side effects of Klonopin include: drowsiness. Other side effects include: upper respiratory tract infection, ataxia, depression, and dizziness. See below for a comprehensive list of adverse effects.

Applies to clonazepam: oral tablet, oral tablet disintegrating

Along with its needed effects, clonazepam (the active ingredient contained in Klonopin) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking clonazepam:

More common

• Body aches or pain
• chills
• cough
• difficulty breathing
• discouragement
• dizziness
• ear congestion
• feeling sad or empty
• fever
• headache
• irritability
• lack of appetite
• loss of interest or pleasure
• loss of voice
• nasal congestion
• poor coordination
• runny nose
• shakiness and unsteady walk
• sleepiness or unusual drowsiness
• sneezing
• sore throat
• tiredness
• trouble concentrating
• trouble sleeping
• unsteadiness, trembling, or other problems with muscle control or coordination
• unusual tiredness or weakness

Less common

• Being forgetful
• bladder pain
• bloody or cloudy urine
• change in speech
• diarrhea
• difficult, burning, or painful urination
• frequent urge to urinate
• general feeling of discomfort or illness
• joint pain
• loss of appetite
• lower back or side pain
• mood or mental changes
• muscle aches and pains
• nausea
• nervousness
• problems in urination or increase in the amount of urine
• shivering
• slurred speech
• sore throat
• sweating
• trouble speaking
• vomiting

Rare

• Burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
• changes in skin color
• chest pain or discomfort
• cold sweats
• colds
• confusion
• cough or hoarseness
• difficulty with sleeping
• dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
• excessive dreaming
• excessive muscle tone
• excitement
• falling
• fast, irregular, pounding, or racing heartbeat or pulse
• feeling mad
• feeling of unreality
• flu-like symptoms
• headache, severe and throbbing
• lack of feeling or emotion
• lack or loss of self-control
• muscle stiffness
• muscle tension or tightness
• nightmares
• pain, inflammation, or swelling in the calves, shoulders, or hands
• pain or swelling in the arms or legs without any injury
• pain, tenderness, or swelling of the foot or leg
• partial or slight paralysis
• scaling
• sense of detachment from self or body
• shakiness in the legs, arms, hands, or feet
• skin rash
• swelling around the eyes
• swelling of the face, ankle, foot, or knees
• thoughts of killing oneself changes in behavior
• tightness in the chest
• trembling or shaking of the hands or feet
• uncaring
• vision changes

Incidence not known

• Abdominal pain or fullness
• anxiety
• black, tarry stools
• bleeding gums
• blood in the urine or stools
• change in consciousness
• chest congestion
• difficulty with coordination
• double vision
• drowsiness
• dry mouth
• feeling that others are watching you or controlling your behavior
• feeling that others can hear your thoughts
• feeling, seeing, or hearing things that are not there
• hyperventilation
• irregular, fast, slow, or shallow breathing
• irregular, twisting uncontrolled movement of the face, hands, arms, or legs
• loss of interest or pleasure
• loss of memory
• loss of strength or energy
• loss of voice
• muscle weakness
• pale or blue lips, fingernails, or skin
• pinpoint red spots on the skin
• problems with memory
• restlessness
• severe mood or mental changes
• sores, ulcers, or white spots on the lips or in the mouth
• swollen glands
• troubled breathing with exertion
• uncontrolled eye movements
• unusual behavior
• unusual bleeding or bruising
• unusual weakness
• vivid dreams
• weight loss or gain

Some side effects of clonazepam may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common

• Decreased interest in sexual intercourse
• difficulty with swallowing
• dryness or soreness of the throat
• heavy bleeding
• hives
• inability to have or keep an erection
• longer than usual time to ejaculation of semen
• loss in sexual ability, desire, drive, or performance
• pain or tenderness around the eyes and cheekbones
• puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
• voice changes

Rare

• Acid or sour stomach
• ankle, knee, or great toe joint pain
• belching
• bleeding after defecation
• blistering, burning, crusting, dryness, or flaking of the skin
• bloated
• blurred or loss of vision
• change in color perception
• cracks in the skin at the corners of the mouth
• decrease or change in vision
• difficulty moving
• double vision
• dryness of the eyes
• earache
• excess air or gas in stomach or intestines
• feeling of constant movement of self or surroundings
• feeling of warmth
• frequent bowel movements
• full feeling
• hair loss or thinning of the hair
• halos around lights
• heartburn
• increased watering of the mouth
• indigestion
• irregularities in menstruation
• itching in the genital or other skin areas
• itching, scaling, severe redness, soreness, or swelling of the skin
• joint stiffness or swelling
• leg or muscle cramps
• loss of taste
• night blindness
• nosebleeds
• overbright appearance of lights
• pain in the breasts or pelvic area
• pain in the leg, nape, or back
• passing gas
• red, sore eyes
• redness of the face, neck, arms, and occasionally, upper chest
• redness or swelling in the ear
• sensation of spinning
• smaller amount of semen ejaculated than usual
• sore on the edge of the eyelid
• soreness or redness around the fingernails and toenails
• stomach discomfort, upset, or pain
• thickening of the tongue
• thirst
• tooth disorder
• toothache
• tunnel vision
• twitching of the eyes
• uncomfortable swelling around the anus
• worsening of acne

Incidence not known

• Burning feeling in the chest or stomach
• difficulty having a bowel movement (stool)
• increased appetite
• increased hair growth, especially on the face
• increased in sexual ability, desire, drive, or performance
• increased interest in sexual intercourse
• sore gums
• tenderness in the stomach area

Applies to clonazepam: oral tablet, oral tablet disintegrating

The most commonly reported side effects included drowsiness, somnolence, ataxia, and behavior problems.

Reversible ataxia, dysarthria, anterograde amnesia, and nystagmus may occur, especially in long-term treatment and/or at high doses.

Transient somnolence, dizziness, ataxia, lightheadedness, muscular hypotonia, and/or coordination disturbances may occur, and usually disappear spontaneously when treatment is continued or upon dose reductions.

Very common (10% or more): Drowsiness (up to 50%), somnolence (up to 50%), ataxia (up to 30%), dizziness (up to 12%)

Common (1% to 10%): Abnormal coordination, dysarthria, intellectual ability reduced, memory disturbance, nystagmus

Rare (0.01% to 0.1%): Convulsions, headache

Very rare (less than 0.01%): Generalized fits, lightheadedness

Frequency not reported: Activation of new types of seizures, amnestic effects, anterograde amnesia/amnesia, aphonia, attention lack, coma, coordination disturbances, decreased movement and gait coordination, disturbance in attention, dysdiadochokinesis/inability to perform rapid, alternating movements, dysphagia, epileptic seizures, extremity numbness and tingling, forgetfulness, head fullness, hemiparesis, hyperactivity, hyperphagia, hypersensitivity to light/noise/physical contact, hypertonia, hypoesthesia, impaired concentration/poor concentration, lethargy, migraine, motion sickness, muscular hypotonia, paresis, paresthesia, seizures, speech slowing/slurring, taste loss, tremor, vertigo, visual field defect

Postmarketing reports: Choreiform movements, hypotonia, preexisting brain damage

Reversible inappropriate behavior may occur, especially in long-term treatment and/or at high doses.

Very common (10% or more): Behavior problems (up to 25%)

Common (1% to 10%): Confusion/confusional state, decreased libido, depression, emotional lability, nervousness

Rare (0.01% to 0.1%): Decrease in sexual drive, loss of libido

Frequency not reported: Aggressive behavior/aggressive reaction/aggression/aggressiveness, agitation, anger, anxiety, apathy, depersonalization, derealization, disorientation, drug withdrawal symptoms, dysphoria, excessive dreaming, excitability/excitement, extreme anxiety, feeling mad, hallucinations, hostility, hysteria, illusion, inappropriate behavior, increased libido, insomnia, irritability, nightmares, organic disinhibition, physical dependence, psychological dependence, psychosis, psychotic disorders, restlessness, sleep disorder, sleep disturbance, suicidal attempt, suicide ideation, tension, vivid dreams, worsening/emergence of clinical depression

Postmarketing reports: Abnormal dreams, change in libido, dependence, encopresis

Very common (10% or more): Upper respiratory tract infection (up to 10%)

Common (1% to 10%): Bronchitis, coughing, pharyngitis, rhinitis, sinusitis

Rare (0.01% to 0.1%): Respiratory depression

Frequency not reported: Asthmatic attach, bronchial hypersecretion/hypersecretion in upper respiratory passages, chest congestion, dyspnea, excessive sneezing, hoarseness, mucus obstruction of the nasopharynx, nosebleed, pneumonia, rhinorrhea, shortness of breath, yawning

Postmarketing reports: Airway obstruction, pharyngeal edema

Common (1% to 10%): Colpitis, dysmenorrhea, ejaculation delayed, impotence, micturition frequency, urinary tract infection

Rare (0.01% to 0.1%): Erectile dysfunction, urinary incontinence

Frequency not reported: Bladder dysfunction, breast pain, dysuria, ejaculation decreased, enuresis/feeling of enuresis, menstrual irregularity, nocturia, pain pelvic, polyuria, urinary retention, urinary tract bleeding, urine discoloration

Transient fatigue, lassitude, slowed reaction, and/or tiredness may occur, and usually disappear spontaneously when treatment is continued or upon dose reductions.

Common (1% to 10%): Fatigue, lassitude, tiredness

Frequency not reported: Accident, drunkenness, earache, fever, herpes simplex infection, hyperacusis, injury, malaise, otitis, pain, paradoxical reaction, reaction slowed/decreased, shivering, thirst, wound

Postmarketing reports: Falls, general deterioration

Common (1% to 10%): Abdominal pain, constipation

Rare (0.01% to 0.1%): Epigastric discomfort/symptoms, gastrointestinal symptoms, nausea

Frequency not reported: Abdominal discomfort, bowel movements frequent, coated tongue, dyspepsia, flatulence, gastrointestinal inflammation, hemorrhoids, pyrosis, salivary hypersecretion/saliva increased/hypersalivation, stomach upset, tongue thick, toothache, tooth disorder, vomiting

Postmarketing reports: Diarrhea, dry mouth, gastritis, sore gums

Common (1% to 10%): Muscle weakness, myalgia

Frequency not reported: Ankle pain, arthralgia, back pain, foot pain, fracture traumatic, knee pain, knee swelling, jaw pain, leg cramps, leg pain, lumbago, muscle cramps, muscle pain, nape pain, shoulder pain, sprains, strains, tendinitis, twitching

Postmarketing reports: Fractures

Common (1% to 10%): Allergic reaction

Rare (0.01% to 0.1%): Angioedema

Frequency not reported: Anaphylaxis

Common (1% to 10%): Blurred vision

Frequency not reported: Diplopia/double vision, eye irritation, eye twitching, periorbital edema, stye, visual disturbance, xerophthalmia

Postmarketing reports: Abnormal eye movements, "glassy-eyed" appearance

Reversible vision disorders (e.g., diplopia) may occur, especially in long-term treatment and/or at high doses.

Common (1% to 10%): Appetite decreased

Frequency not reported: Anorexia, dehydration, gout, hunger abnormal, increased appetite, weight gain, weight loss

Common (1% to 10%): Influenza

Frequency not reported: Infection mycotic, infection streptococcal, infection viral, moniliasis

Rare (0.01% to 0.1%): Pigmentation changes, pruritus, rash/skin rash, transient hair loss, urticaria

Frequency not reported: Abrasions, acne flare, alopecia/transient hair loss, bleeding dermal, burning skin, cellulitis, dermatitis contact, facial edema, hair loss, hirsutism, pustular reaction, skin disorder, sweating, xeroderma

Postmarketing reports: Angioneurotic edema, pigmentation disorder

Rare (0.01% to 0.1%): Decreased platelet count

Frequency not reported: Anemia, blood dyscrasias, eosinophilia, infectious mononucleosis, leukopenia, lymphadenopathy

Postmarketing reports: Thrombocytopenia

Frequency not reported: Ankle edema, chest pain, edema, flushing, foot edema, palpitations, postural hypotension, tachycardia, thrombophlebitis leg

Postmarketing reports: Cardiac arrest, cardiac failure, thrombophlebitis, thrombosis

Tachycardia occurred after IV administration.

Frequency not reported: Abnormal liver function tests, hepatomegaly

Postmarketing reports: Transient elevations of serum transaminases and alkaline phosphatase

Frequency not reported: Incomplete precocious puberty/premature secondary sex characteristics

Frequency not reported: Localized inflammation

Frequency not reported: Cystitis