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Dextromethorphan / quinidine Side Effects

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

For the Consumer

Applies to dextromethorphan / quinidine: oral capsule

In addition to its needed effects, some unwanted effects may be caused by dextromethorphan / quinidine. 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 dextromethorphan / quinidine:

Less common
  • Bladder pain
  • bloating or swelling of the face, arms, hands, lower legs, or feet
  • bloody or cloudy urine
  • chills
  • cough
  • diarrhea
  • difficult, burning, or painful urination
  • fever
  • frequent urge to urinate
  • general feeling of discomfort or illness
  • headache
  • joint pain
  • loss of appetite
  • lower back or side pain
  • muscle aches and pains
  • nausea
  • rapid weight gain
  • runny nose
  • shivering
  • sore throat
  • sweating
  • tingling of the hands or feet
  • trouble sleeping
  • unusual tiredness or weakness
  • unusual weight gain or loss
  • vomiting

If any of the following symptoms of overdose occur while taking dextromethorphan / quinidine, get emergency help immediately:

Symptoms of overdose
  • Aggressive and violent behavior
  • agitation
  • blurred vision
  • change in color vision
  • change in consciousness
  • chest pain or discomfort
  • confusion
  • confusion as to time, place, or person
  • continuing ringing or buzzing or other unexplained noise in the ears
  • decreased awareness or responsiveness
  • depression
  • difficulty seeing at night
  • dizziness or lightheadedness
  • dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
  • double vision
  • excitement
  • fainting
  • fast, pounding, or irregular heartbeat or pulse
  • feeling of constant movement of self or surroundings
  • hallucinations
  • hearing loss
  • holding false beliefs that cannot be changed by fact
  • inability to move the eyes
  • increased blinking or spasms of the eyelid
  • increased sensitivity of the eyes to sunlight
  • irregular or slow heart rate
  • loss of consciousness
  • overactive reflexes
  • poor coordination
  • restlessness
  • seeing double
  • seizures
  • sensation of spinning
  • severe sleepiness
  • shakiness and unsteady walk
  • shivering
  • shortness of breath
  • sticking out of tongue
  • sweating
  • talking or acting with excitement you cannot control
  • trembling or shaking
  • trouble with breathing, speaking, or swallowing
  • twitching
  • uncontrolled eye movements
  • uncontrolled twisting movements of the neck, trunk, arms, or legs
  • unsteadiness, trembling, or other problems with muscle control or coordination
  • unusual excitement, nervousness, or restlessness
  • unusual facial expressions

Some of the side effects that can occur with dextromethorphan / quinidine 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:

Less common
  • Bloated
  • excess air or gas in the stomach or intestines
  • full feeling
  • lack or loss of strength
  • passing gas

For Healthcare Professionals

Applies to dextromethorphan / quinidine: oral capsule

Nervous system

Nervous system side effects have included drowsiness, dizziness, asthenia, nervousness, and restlessness.[Ref]


Gastrointestinal side effects have included diarrhea, vomiting, flatulence, and abdominal pain.[Ref]


Musculoskeletal side effects have included muscle spasticity and muscle spasms.[Ref]


Respiratory side effects have included cough and respiratory failure.[Ref]


Genitourinary side effects have included urinary tract infection.[Ref]


General side effects have included influenza and increased gamma-glutamyltransferase.[Ref]


Cardiovascular side effects have included peripheral edema.[Ref]


1. "Product Information. Nuedexta (dextromethorphan-quinidine)." Avanir Pharmaceuticals, Inc, Aliso Viejo, CA.

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