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Dextromethorphan / quinidine Side Effects

Medically reviewed by Last updated on Feb 25, 2024.

Applies to dextromethorphan / quinidine: oral capsule.

Serious side effects

Along with its needed effects, dextromethorphan/quinidine 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 dextromethorphan / quinidine:

Less common

Get emergency help immediately if any of the following symptoms of overdose occur while taking dextromethorphan / quinidine:

Symptoms of overdose

Other side effects

Some side effects of dextromethorphan / quinidine 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

For Healthcare Professionals

Applies to dextromethorphan / quinidine: oral capsule.


The most commonly reported adverse reactions (2% or greater incidence and greater than placebo) that led to treatment discontinuation were muscle spasticity, abdominal pain, asthenia, dizziness, muscle spasms, respiratory failure, and fall.[Ref]


Very common (10% or more): Diarrhea (13%)

Common (1% to 10%): Abdominal pain, vomiting, flatulence


Postmarketing reports: Nausea, vomiting, stomach pain[Ref]

Nervous system

Very common (10% or more): Dizziness (10%)


Postmarketing reports: Drowsiness, dizziness, nervousness, restlessness


Postmarketing reports: Convulsions, apprehension, ataxia, acute psychotic reactions (rare)[Ref]


Frequency not reported: QTc prolongation[Ref]


Common (1% to 10%): Muscle spasticity, muscle spasms[Ref]


Common (1% to 10%): Increased gamma-glutamyltransferase[Ref]


Common (1% to 10%): Respiratory failure, cough[Ref]


Common (1% to 10%): Asthenia, fall, peripheral edema


Postmarketing reports: Cinchonism[Ref]

Cinchonism is usually a sign of chronic quinidine toxicity, but it may appear in sensitive patients after a single moderate dose of several hundred milligrams. It is characterized by nausea, vomiting, diarrhea, tinnitus headache, hearing loss, vertigo, blurred vision, diplopia, photophobia, confusion, and delirium.[Ref]


Common (1% to 10%): Influenza[Ref]


Common (1% to 10%): Urinary tract infection[Ref]



Postmarketing reports: Mydriasis, disturbed color perception, night blindness, scotomata, optic neuritis, visual field loss, photosensitivity, keratopathy[Ref]



Postmarketing reports: Skin pigmentation abnormalities[Ref]



Postmarketing reports: Depression[Ref]


1. (2010) "Product Information. Nuedexta (dextromethorphan-quinidine)." Avanir Pharmaceuticals, Inc

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.